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Informix Guide to SQL: Tutorial, Version 6.0

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1. CREATE TABLE taxrates column specifications IN misctabs You can achieve many aims by placing a table in a specific dbspace Some of these aims are explored in the following paragraphs Exploiting Mirroring Place all the tables used by a critically important application in a mirrored dbspace Alternatively create the database in the mirrored dbspace and let the important tables reside there by default Tables that are part of the data base but that are not used by the critical programs can be located in nonmirrored spaces Sharing Temporary Space When databases are large and disk space is limited the normal dbspaces might not have enough room for those large temporary tables that can be helpful in improving query performance However a temporary table exists only for the life of the program that creates it even less time if the program drops the table promptly Set up a single dbspace for temporary tables so it can be used repeatedly by many programs Assigning Dedicated Hardware A dbspace can equal a chunk and a chunk can equal a device Thus you can place a table on a disk device that is dedicated to its use When disk drives have different performance levels you can put the tables with the highest frequency of use on the fastest drives By giving a high use table a dedicated access arm you can reduce contention with applications that use other tables This does not reduce contention between programs
2. Optimizing Your Queries 13 23 Time Costs of a Query The expression O paid_date IS NULL filters out some rows reducing the number of rows that are used from the orders table As before two query plans are possible The plan that starts by reading from orders is displayed in pseudocode in Figure 13 3 for each row in the orders table do read the row into O if O paid_date is null then for each row in the customer table do read the row into C if O customer_num C customer_num then let Sum 0 for each row in the items table do read the row into I if I order_num O order_num then let Sum Sum I total_price end if end for prepare an output row from C I and Sum end if end for end if end for Figure 13 3 One of two query plans in pseudocode Let pdnull represent for the number of rows in orders that pass the filter It is the number that the following query returns SELECT COUNT FROM orders WHERE paid_date IS NULL Assume that just one customer exists for every order as there should be Then we can say that the plan in Figure 13 3 reads the following rows e All rows of the orders table once e All rows of the customer table pdnull times e All rows of the items table pdnull times 13 24 Optimizing Your Queries Time Costs of a Query Figure 13 4 An alternative plan is shown in Figure 13 4 it reads from customer first for each row in the customer table do read the row into C
3. Granting and Limiting Access to Your Database 11 13 Granting Privileges Figure 11 2 Unfortunately although INFORMIX 4GL allows you to mix GRANT and REVOKE statements freely with other program statements it does not permit you to create parameters from them from program variables To customize a GRANT statement with a user id taken from user input the program must build the statement as a string prepare it with a PREPARE statement and exe cute it with an EXECUTE statement These statements are discussed in detail in Chapter 5 Programming with SQL where the following example is analyzed in detail Figure 11 2 shows one possible definition of the 4GL function table_grant that is invoked by the CALL statement in the preceding example FUNCTION table_grant priv_to_grant table_name user_id DEFINE priv_to_grant char 100 may include column list table_name CHAR 20 user_id CHAR 20 grant_stmt CHAR 200 LET grant_stmt GRANT priv_to_grant ON table_name TO user_id WHENEVER ERROR CONTINUE PREPARE the_grant FROM grant_stmt IF status 0 THE EXECUTE the_grant END IF IF status lt gt 0 THEN DISPLAY Sorry got error status attempting DISPLAY grant_stmt END IF WHENEVER ERROR STOP END FUNCTION A 4GL function that builds prepares and executes a GRANT statement Automating with a Command Script Your operating system probably s
4. personal computer application databases Figure 12 1 A database management system on a personal computer The components of the system in Figure 12 1 are found in the following list e An application program Any program that issues a query can be the application It could for example be a program written in INFORMIX 4GL a C language program with embedded SQL or compiled screen forms and reports e A connection On a simple system such as this one the communication component is frequently so well integrated with the system that it is usually omitted from diagrams and not discussed However it does exist e A database server The database server receives queries from the application searches the database and returns information to the application The database server manages or administers the databases that it controls Because Figure 12 1 illustrates a personal computer the database server must be INFORMIX SE The database server in this diagram is a local server because it resides on the same host computer as the client application Understanding Informix Networking 12 5 Database Management System Configurations Databases The databases are usually stored on a magnetic disk If this system were a UNIX system with INFORMIX OnLine Dynamic Server the database might be located on some other medium such as a WORM write once read many times drive controlled by INFORMIX OnLine Optical Advant
5. COMMIT WORK DEFINE ord_row RECORD LIKE orders last_ord LIKE orders order_num DECLARE dup_row CURSOR FOR SELECT FROM ORDERS main INTO ord_row WHERE 1 lt SELECT COUNT FROM ORDERS minor WHERE main order_num minor order_num ORDER BY order_date ECLARE ins_row CURSOR FOR INSERT INTO new_orders VALUES ord_row is BEGIN WORK OPEN ins_row L F ET last_ord 1 OREACH dup_row IF ord_row order_num lt gt last_ord THEN PUT ins_row LET last_ord ord_row order_num END IF END FOREACH CLOSE ins_row COMMIT WORK A AGL program that re creates a table without duplicates This example begins with an ordinary INSERT statement that finds all the nonduplicated rows of the table and inserts them into another table presum ably created before the program started That leaves only the duplicate rows Remember in the demonstration database the orders table has a unique index and cannot have duplicate rows This example deals with some other database In INFORMIX 4GL you can define a data structure like a table the structure is automatically given one element for each column in the table The ord_row structure is a buffer to hold one row of the table The code in Figure 6 5 then declares two cursors The first called dup_row returns the duplicate rows in the table Because it is for input only it can use the ORDER BY clause to impose some order on the duplicates other than the physical
6. Query 2 13 Composing Simple SELECT Statements 2 19 Single Table SELECT Statements Query 2 13 limits the display to show each customer number in the orders table only once producing a more readable list as shown in Query Result 2 13 customer_num 101 104 106 110 111 112 115 116 117 119 120 121 122 123 124 126 127 Query Result 2 13 Suppose you are handling a customer call and you want to locate purchase order number DM354331 You decide to list all the purchase order numbers in the orders table using a statement such as the one in Query 2 14 SELECT po_num FROM orders Query 2 14 2 20 Composing Simple SELECT Statements Single Table SELECT Statements Query Result 2 14 shows how the statement retrieves data in the po_num column in the orders table po_num B77836 9270 B77890 8006 2865 Q13557 278693 LZ230 4745 429Q B77897 278701 B77930 8052 A003 PC6782 DM354331 S22942 259709 W2286 C3288 W9925 KF2961 Query Result 2 14 Composing Simple SELECT Statements 2 21 Single Table SELECT Statements However the list is not in a very useful order You can add an ORDER BY clause to sort the column data in ascending order and make it easier to find that particular po_num as shown in Query 2 15 SELECT po_num FROM orders ORDER BY po_num Query 2 15 po_num 278693 278701 2865 4290 4745 8006 8052 9270 B77836 B77890 B77897 B77930 C3288 DM354331
7. Query 3 41 creates a list where the California customers the ones called most frequently appear first as shown in Query Result 3 41 sortkey 1 lname Baxter fname Dick company Blue Ribbon Sports city Oakland State CA phone 415 655 0011 sortkey 1 lname Beatty fname Lana company Sportstown city Menlo Park state CA phone 415 356 9982 sortkey 1 lname Currie fname Philip company Phil s Sports city Palo Alto state CA phone 415 328 4543 sortkey 1 lname Grant fname Alfred company Gold Medal Sports city Menlo Park state CA phone 415 356 1123 sortkey 2 iname Satifer fname Kim company Big Blue Bike Shop city Blue Island state NY phone 312 944 5691 sortkey 2 lname Shorter fname Bob company The Triathletes Club city Cherry Hill state NJ phone 609 663 6079 sortkey 2 lname Wallack fname Jason company City Sports city Wilmington state DE phone 302 366 7511 Query Result 3 41 3 50 Composing Advanced SELECT Statements Set Operations Intersection The intersection of two sets of rows produces a table containing rows that exist in both of the original tables Use the keyword EXISTS or IN to introduce sub queries that show the intersection of two sets Figure 3 2 illustrates the intersection set operation SELECT stock_num manu_code unit_price FROM stock WHERE stock_num IN SELECT stock_num FROM items stock_num ORDER BY stock_num exists in not in stock table ite
8. Run Next Restart Exit Display the next page of query results 1019 Bob Shorter SHM swim cap 07 16 93 Figure 1 3 Querying a database Modifying Data The model also makes it possible to modify the contents of the database with less chance for error You can query the database with commands such as Find every stock item with a manufacturer of Presta or Schraeder and increase its price by 13 percent You state changes in terms that reflect the meaning of the data You do not have to waste time and effort thinking about details of fields within records in a file so the chances for error are less The statements you use to modify stored data are covered in Chapter 5 Pro gramming with SQL Concurrent Use and Security A database can be a common resource for many users Multiple users can query and modify a database simultaneously The database server the pro gram that manages the contents of all databases ensures that the queries and modifications are done in sequence and without conflict 1 8 Introducing Database Features and SQL Databases What and Why Having concurrent users on a database provides great advantages but also introduces new problems of security and privacy Some databases are pri vate individuals set them up for their own use Other databases contain con fidential material that must be shared but among only a select group of persons Still other databases provide public access Informix
9. 10 14 Tuning Your Data Model the sum of the maximum sizes of all columns in the table plus 4 bytes Treat TEXT and BYTE columns as having size 56 the sum of the estimated typical sizes of all columns in the table plus 4 bytes if typrow lt pageuse then typrow lse 4 remainder typrow pageuse Let homerow be the amount of a typical row that fits on the home page it is typrow if one page is sufficient Figure 10 7 overpage homemax datrows datpages expages Calculating Table Sizes if typrow lt pageuse then 0 else floor typrow pageuse Let overpage be the number of expansion pages needed for the typical row it is zero when a typical row fits on a page if maxrow lt pageuse then maxrow lse 4 remainder maxrow pageuse Let homemax be the reserve requirement of the database server floor pageuse homemax typrow Let datrows be the number of typical rows that fits on a page before the database server decides the page is full ceiling estrows datrows estrows X overpage The table requires approximately datpages expages disk pages for rows Additional pages for TEXT and BYTE columns are estimated in Estimating Blobpages on page 10 17 An estimate for the catalog table is shown in Figure 10 6 Variable Estimate Basis of Estimate estrows 5 000 company business plan pagesize 2 048 output of onstat pageuse 2 020 pagesize 28 maxrow 381 sum of 4
10. 1 concatenation operator 1 432S Index 51 52 Index Reader Response Card Informix Guide to SQL Tutorial Version 6 0 Dear Reader At Informix Software we think documentation is very important After all manuals are an integral part of our product line Because documentation is important we want to know what you think about our manuals You can tell us by filling out and returning the Reader Response Card Thanks for your help 1 Overall how do you rate this manual Outstanding Very good Good C Average Poor 2 Is the manual effective e Is it organized so you can find things O Yes O No e Is the index adequate Yes No e Is the table of contents easy to use Yes No e If applicable do you find the statement syntax readable Yes No e Are topics presented in a useful sequence Yes No e Are the examples useful Yes No 3 What did you think of the level of description e Writing quality Very good Good Average CI Poor e Clarity Very clear Average Hard to understand Level Too technical Just right Oversimplified 4 When you need to find information quickly which part of the documentation do you u
11. Cursor Stability ensures that a row does not change while the program examines it This is important when the program updates some other table based on the data it reads from this row Because of Cursor Stability the pro gram is assured that the update is based on current information It prevents the use of stale data Here is an example to illustrate this point In terms of the demonstration database Program A wants to insert a new stock item for manufacturer Hero Concurrently program B wants to delete manufacturer Hero and all stock associated with it The following sequence of events can occur 1 Program A operating under Cursor Stability fetches the Hero row from the manufact table to learn the manufacturer code This places a shared lock on the row 2 Program B issues a DELETE statement for that row Because of the lock the database server makes the program wait 3 Program A inserts a new row in the stock table using the manufacturer code it obtained from the manufact table 4 Program A closes its cursor on the manufact table or reads a different row of it releasing its lock 5 Program B released from its wait completes the deletion of the row and goes on to delete the rows of stock that use manufacturer code HRO including the row just inserted by Program A If Program A used a lesser level of isolation the following sequence could have happened 1 Program A reads the Hero row of the manufact table to learn th
12. ECT stock_num manu_code FROM items WHERE quantity gt 3 ORDER BY 2 Query 3 37 The compound query in Query 3 37 selects the same rows as Query 3 36 but displays them in order of manufacturer code as shown in Query Result 3 37 stock_num manu_code 5 ANZ 9 ANZ 302 HRO 301 KAR 302 KAR 201 NKL 5 NRG 103 PRC 106 PRC 5 SMT Query Result 3 37 Composing Advanced SELECT Statements 3 45 Set Operations By default the UNION keyword excludes duplicate rows Add the optional keyword ALL as shown in Query 3 38 to retain the duplicate values SELECT stock_num manu_code FROM stock WHER UNION ALL E unit_price lt 25 00 SELECT stock_num manu_code FROM WHER ORDE items E quantity gt 3 R BY 2 INTO TEMP stockitem Query 3 38 Query 3 38 uses the UNION ALL keywords to unite two SELECT statements and puts the results into a temporary table by adding an INTO TEMP clause after the final SELECT It returns the same rows as Query 3 37 but also includes duplicate values stock_num ano uw uw 302 302 301 201 103 106 5 5 manu_code ANZ ANZ ANZ ANZ ANZ ANZ ANZ ANZ HRO KAR KAR NKL NRG NRG PRC PRC SMT SMT Query Result 3 38 Corresponding columns in the select lists for the combined queries must have identical data types but the columns do not need to use the same identifier 3 46 Composing Advanced SELECT Statements Set Operations Query 3 3
13. Committed Read Isolation When a program requests the Committed Read isolation level INFORMIX OnLine Dynamic Server guarantees that it never returns a row that is not committed to the database This prevents the situation in number 4 in the list of concurrency issues on page 7 5 reading data that is not committed and that is subsequently rolled back Committed Read is implemented very simply Before fetching a row the database server tests to determine whether an updating process placed a lock on the row If not it returns the row Because rows that are updated but not committed have locks on them this test ensures that the program does not read uncommitted data Committed Read does not actually place a lock on the fetched row hence it is almost as efficient as Dirty Read It is appropriate for use when each row of data is processed as an independent unit without reference to other rows in the same or other tables 7 10 Programming for a Multiuser Environment Setting the Isolation Level Cursor Stability Isolation The next level is called Cursor Stability When it is in effect the database server places a lock on the latest row fetched It places a shared lock for an ordinary cursor or a promotable lock for an update cursor Only one row is locked at a time that is each time a row is fetched the lock on the previous row is released unless that row is updated in which case the lock holds until the end of the transaction
14. RETURNING INT CHAR 10 EFINE ncalls INT DEFINE o_name CHAR 10 J RETURN ncalls o_name END PROCEDURE If you neglect to include a RETURN statement you do not get an error message at compile time Returning More Than One Set of Values from a Procedure If your procedure performs a select that can return more than one row from the database or if you return values from inside a loop you must use the WITH RESUME keywords in the RETURN statement Using a RETURN WITH RESUME statement causes the value or values to be returned to the calling program or procedure After the calling program receives the values execu tion returns to the statement immediately following the RETURN WITH RESUME statement Figure 14 13 is an example of a cursory procedure It returns values from a FOREACH loop and a FOR loop This procedure is called a cursory procedure because it contains a FOREACH loop 14 26 Creating and Using Stored Procedures Exception Handling CREATE PROCEDURE read_many lastname CHAR 15 RETURNING CHAR 15 CHAR 15 CHAR 20 CHAR 15 CHAR 2 CHAR 5 DEFINE p_lname p_fname p_city CHAR 15 DEFINE p_add CHAR 20 DEFINE p_state CHAR 2 DEFINE p_zip CHAR 5 DEFINE lcount INT DEFINE i INT ry B LET lcount 0 TRACE ON CREATE VIEW myview AS SELECT FROM customer RACE Foreach starts FOREACH SELECT fname lname addressl city state zipcode INTO p_fname p_lname
15. The optimizer uses an index to process a filter that tests an initial substring of an indexed column However the presence of the substring test can interfere with the use of a composite index to test both the substring column and another column Rethinking the Query After you understand what the query is doing look for ways to obtain the same output with less effort The following suggestions can help you rewrite your query more efficiently e Rewriting joins through views e Avoiding or simplifying sorts e Eliminating sequential access to large tables e Using unions to avoid sequential access Rewriting Joins Through Views You might find that the query joins a table to a view that is itself a join If you rewrite the query to join directly to fewer tables you might produce a simpler query plan Avoiding or Simplifying Sorts A sort is not necessarily negative The sort algorithm of the database server is highly tuned and extremely efficient It is certainly as fast as any external sort program you might apply to the same data As long as the sort is per formed only occasionally or to a relatively small number of output rows no need exists to avoid it Optimizing Your Queries 13 33 Making Queries Faster However you should avoid or simplify repeated sorts of large tables The optimizer avoids a sort step whenever it can produce the output in its proper order automatically by using an index The following factors prevent
16. The second vendor contains data about the vendors who provide the parts The third parven records which parts are available from which vendors and at what price part vendor part num part_desc vendor_num_ vendor_name pk pk 100 000 spiral spanner 9 100 000 Wrenchers SA 999 999 spotted paint 9 999 999 Spottiswode parven part_num vendor_num price pk fk pk fk 100 000 9 100 000 14 98 999 999 9 999 999 0 066 Figure 13 6 Three tables from a manufacturing database The following query is run regularly against these tables to produce a report of all available prices SELECT part_desc vendor_name price FROM part vendor parven WHERE part part_num parven part_num AND parven vendor_num vendor vendor_num ORDER BY part part_num Although it appears to be a relatively simple three table join the query takes too much time As part of your investigation prepare a table showing the approximate sizes of the tables and their indexes in pages The table appears in Figure 13 7 It is based on a disk page size of 4 096 bytes Only approximate numbers are used The actual number of rows changes often and only estimated calculations are made in any case On further investigation you learn that the index on part_num is clustered so that the part table is in physical order by part_num Similarly the vendor table is in physical order by vendor_num The parven table is not
17. base however has a role assigned to it by the data model It may be a price that is associated with a product that was sold as one item of an order that was placed by a customer Each of these things prices products items orders and customers are also roles specified by the data model See Figure 1 1 The data model is designed when the database is created then units of data are inserted according to the plan laid out in the model In some books the term schema is used instead of data model 1 4 Introducing Database Features and SQL Databases What and Why 1015 06 27 93 1 case baseball gloves 450 00 1014 06 25 93 1 case football 960 00 1013 06 22 93 1 each tennis racquet 19 80 1012 06 18 93 1 case volleyball 840 00 1011 06 18 93 5 each tennis racquet 99 00 1010 06 17 93 1 case tennis ball 36 00 ORDERS order 1003 05 22 93 customer Anthony Higgins 05 20 93 item tennis racquet order 1011 06 18 93 order 1013 06 22 93 19 80 item 1 case tennis ball volleyball nets Figure 1 1 Illustration of a data model Introducing Database Features and SQL 1 5 Databases What and Why Storing Data Another difference between a database and a file is that the organization of the database is stored with the database A file may have a complex inner structure but the def
18. second Set to W when a column value is truncated as it is fetched into a host variable third Set to W when an aggregate function encounters a null value fourth On a SELECT or on opening a cursor set to W when the number of items in the select list is not the same as the number of host variables given in the INTO clause to receive them fifth Set to W when any part of a statement involves a host database server which stores the FLOAT data type in DECIMAL form done when the host system lacks support for FLOAT types sixth Set to W following execution of a statement that does not use ANSI standard SQL syntax provided that the DBANSIWARN environment variable is set yee Not used il Not used character 71 OAN Contains the variable such as table name that is placed in the error message For some networked applications contains an error message generated by networking software Figure 5 5 The uses of SQLAWARN and SQLERRM 5 10 Programming with SQL Calling the Database Server In particular the subscript by which you name one element of the SQLERRD and SQLAWARN arrays differs array elements are numbered starting with zero in INFORMIX ESQL C but starting with one in the other languages In this discussion the fields are named using specific words such as third and you must translate into the syntax of your programming language The SOLCODE Field The SQLCODE field is the primary return code of the database ser
19. 0 1 4 Dh 07 23 07 24 06 8 06 27 07 24 07 1 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 06 004 2 006 7 007 7 012 9 016 20 017 01 002 04 003 6 005 06 014 0 008 04 001 04 013 AL 018 22 019 11 009 15 010 24 021 27 023 04 011 10 015 26 022 23 020 po_num 8006 Q13557 278693 278701 PC6782 DM354331 9270 B77890 2865 8052 LZ230 B77836 B77930 522942 Z55709 4745 4290 C3288 KF2961 B77897 MA003 Ww9925 W2286 Composing Simple SELECT Statements 2 23 Single Table SELECT Statements When you use SELECT and ORDER BY on several columns in a table you might find it helpful to use integers to refer to the position of the columns in the ORDER BY clause The statements in Query 2 17 retrieve and display the same data shown in Query Result 2 17 SELECT customer_num order_num po_num order_date FROM orders ORDER BY 4 1 SELECT customer_num order_num po_num order_date FROM orders ORDER BY order_date customer_num Query 2 17 customer_num order_num po_num order_date 104 1001 B77836 05 20 1993 101 1002 9270 05 21 1993 104 1003 B77890 05 22 1993 106 1004 8006 05 22 1993 116 1005 2865 05 24 1993 112 1006 Q13557 05 30 1993 117 1007 278693 05 31 1993 110 1008 LZ230 06 07 1993 111 1009 4745 06 14 1993 115 1010 4290 06 17 1993 104 1011 B77897 06 18 1993 117
20. 0 3 reserving 10 percent for small tables and overhead e Give each table one fourth of its share of the dbspace as its initial extent e Assign each table one eighth of its share as its next extent size Monitor the growth of the tables regularly using oncheck What happens if as the dbspace fills up you do not have enough contiguous space to create an extent of the size you specified In that case OnLine allocates the largest contiguous extent that it can Tuning Your Data Model 10 9 INFORMIX OnLine Dynamic Server Disk Storage Upper Limit on Extents No table should be allowed to acquire a large number of extents But it can happen and an upper limit exists on the number of extents allowed Trying to add an extent after the limit is reached causes ISAM error 136 No more extents to follow an INSERT request The upper limit depends on the page size and the table definition To learn the upper limit on extents for a particular table calculate a series of values as shown in the following list pagesize the size of a page reported by onstat c under the head BUFFSIZE colspace 4 x the number of columns in the table ixspace 12 x the number of indexes on the table ixparts 4 x the number of columns named in each index extspace pagesize colspace ixspace ixparts 84 The table can have no more than extspace 8 extents When the page size is 2 048 the customer table from the demonstration database can have no
21. 1 294S database 1 422S index 1 419S 1 484S 1 505S table 1 84S 1 470S 1 507S See also Database Name segment See also Index Name segment See also Table Name segment Naming conventions tables 12 16T Native Language Support See NLS Natural join 2 75T NCHAR data type description of 3 17R 9 15T syntax 1 425S versus CHAR data type 1 19R Nested ordering in SELECT 1 339S 2 15T Network computer 12 4T connection information 12 15T data sent over 13 21T performance of 13 20T simple model of 13 21T site 12 4T Network environment variable DBPATH 4 21R SQLRM 4 42R SQLRMDIR 4 43R NEW keyword in DELETE REFERENCING clause 1 119S in INSERT REFERENCING clause 1 118S in UPDATE REFERENCING clause 1 120S NEXT keyword syntax in FETCH 1 1945 use in FETCH 1 196S NEXT SIZE keywords specifying size of extents 10 8T use in CREATE TABLE 1 107S use in GRANT 1 2335 NLS 1 14R activating 2 25T activating in Informix products 1 16R and collation order 2 25T and dbexport utility 5 12R and dbimport utility 5 13R and MATCHES keyword 2 42T and ORDER BY keywords 2 25T 2 42T checking products for functionality 1 18R COLLCHAR environment variable 4 45R creating character mapping files for 5 5R data types for 1 19R database server compatibility 1 19R DBAPICODE environment variable 4 47R DBNLS environment variable 4 48R environment variables listed 4 9R error messages for incompatibility 1 21R functionality in In
22. 95 42 87 97 75 102 4 5 36 48 170 280 160 190 250 40 40 00 00 00 00 00 00 00 00 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 99 00 00 00 50 00 00 00 00 00 00 00 50 00 00 00 00 50 00 00 00 00 00 00 00 00 00 00 Difference Set Operations The difference between two sets of rows produces a table containing rows in the first set that are not also in the second set Use the keywords NOT EXISTS or NOT IN to introduce subqueries that show the difference between two sets Figure 3 3 illustrates the difference set operation SELECT stock_num manu_code unit_price FROM stock WHERE stock_num NOT IN SELECT stock_num FROM items stock_num ORDER BY stock_num exists in notin stock table items table items table stock_num exists in aes 3 qualifies stock table items table not in stock table Figure 3 3 The difference set operation Query 3 43 is an example of a nested SELECT statement that shows the difference between the stock and items tables SELECT stock_num manu_code unit_price FROM stock WHI ERE stock_num NOT IN SELECT stock _num FROM items OR DER BY stock_num Query 3 43 Composing Advanced SELECT Statements 3 53 Summary Query Result 3 43 contains all the elements from only the first set returning the f
23. AND o customer_num gt 110 AND o order_num i order_num GROUP BY 1 3 HAVING COUNT lt 5 ORDER BY 3 INTO TEMP temptabl Query 3 8 3 10 Composing Advanced SELECT Statements Creating Advanced Joins Query 3 8 joins the orders and items tables employs display labels table aliases and integers used as column indicators groups and orders the data and puts the following results ina temporary table as shown in Query Result 3 8 order_num price span 1017 584 00 1016 654 00 1012 1040 00 1019 1499 97 26 1005 562 00 28 1021 1614 00 30 1022 232 00 40 1010 84 00 66 1009 450 00 68 1020 438 00 71 Query Result 3 8 Creating Advanced Joins Chapter 2 Composing Simple SELECT Statements showed how to include a WHERE clause in a SELECT statement to join two or more tables on one or more columns It illustrated natural joins and equi joins This chapter discusses the uses of two more complex kinds of joins self joins and outer joins As described for simple joins you can define aliases for tables and assign display labels to expressions to shorten your multiple table que ries You can also sort data with an ORDER BY clause and SELECT query results into a temporary table Self Joins A join does not always have to involve two different tables You can join a table to itself creating a self join This can be useful when you want to compare values in a column to other values in the same column To
24. SELECT c customer_num c lname c company c phone u call_dtime u call_descr FROM customer c cust_calls u WHERE c customer_num u customer_num Query 3 21 3 22 Composing Advanced SELECT Statements Creating Advanced Joins Query 3 21 returns only those rows where the customer has made a call to customer service as shown in Query Result 3 21 customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr Query Result 3 21 06 Watson Watson amp Son 415 389 8789 993 06 12 08 20 Order was received but two of the cans of ANZ tennis balls within the case were empty 0 Jaeger AA Athletics 415 743 3611 993 07 07 10 24 Order placed one month ago 6 7 not received 9 Shorter The Triathletes Club 609 663 6079 993 07 01 15 00 Bill does not reflect credit from previous order 21 Wallack City Sports 302 366 7511 993 07 10 14 05 Customer likes our merchandise stock more types of infant joggers to place order Requests that we Will call back 27 Satifer Big Blue Bike Shop 312 944 5691 993 07 31 14 30 Received Hero
25. The basis of a view is a SELECT statement When you create a view you define a SELECT statement that generates the contents of the view at the time the view is accessed A user also queries a view using a SELECT statement The database server merges the SELECT statement of the user with the one defined for the view and then actually performs the combined statements The result has the appearance of a table it is enough like a table that a view even can be based on other views or on joins of tables and other views Granting and Limiting Access to Your Database 11 19 Using Views Because you write a SELECT statement that determines the contents of the view you can use views for any of the following purposes To restrict users to particular columns of tables You name only permitted columns in the select list in the view To restrict users to particular rows of tables You specify a WHERE clause that returns only permitted rows To constrain inserted and updated values to certain ranges You can use the WITH CHECK OPTION discussed on page 11 25 to enforce constraints To provide access to derived data without having to store redundant data in the database You write the expressions that derive the data into the select list in the view Each time you query the view the data is derived anew The derived data is always up to date yet no redundancies are introduced into the data model To hide the details of a complicated SELECT st
26. Warnings provide critical A database Additionally when you are instructed to enter or execute text immediately press RETURN after the entry When you are instructed to type the text or press a key no RETURN is required Example Code Conventions Examples of SQL code occur throughout this manual Except where noted the code is not specific to any single Informix application development tool If only SQL statements are listed in the example they are not delineated by semicolons To use this SQL code for a specific product you must apply the syntax rules for that product For example if you are using the Query language option of DB Access you must delineate multiple statements with semicolons If you are using an SQL API you must use EXEC SQL and a semi colon or other appropriate delimiters at the start and end of each statement respectively Introduction 5 Useful On Line Files For example you might see the following example code CONNECT TO stores6 DELETE FROM customer WHERE customer_num 121 COMMIT WORK DISCONNECT CURRENT For detailed directions on using SQL statements for a particular application development tool or SQL API see the manual for your product Also note that dots in the example indicate that more code would be added in a full application but it is not necessary to show it to describe the concept being discussed Useful On Line Files 6 Introduction In add
27. accounts and a child table sub_accounts The following CREATE TABLE statements define the referential constraints CREATE TABLE accounts acc_num SERIAL primary key acc_type INT acc_descr CHAR 20 CREATE TABLE sub_accounts sub_acc INTEGER primary key ref_num INTEGER REFERENCES references accounts acc_num ON DELETE CASCADE sub_descr CHAR 20 Modifying Data 4 21 Interrupted Modifications Notice that the primary key of the accounts table the acc_num column uses a SERIAL data type and the foreign key of the sub_accounts table the ref_num column uses an INTEGER data type Combining the SERIAL data type on the primary key and the INTEGER data type on the foreign key is allowed This is the only condition where you can mix and match data types The SERIAL data type is an INTEGER and the values for the column are auto matically generated by the database All other primary and foreign key com binations must match explicitly For example a primary key defined as CHAR must match a foreign key defined as CHAR To delete a row from the accounts table that will cascade a delete to the sub_accounts table you must turn on logging After logging is turned on you can delete the account number 2 from both tables as shown in the following example DELETE FROM accounts WHERE acc_num 2 Restrictions on Cascading Deletes You can use cascading deletes for most deletes including deletes on self referencing and
28. applied to several customers Instead of updating the customer table each time a change is reported the new addresses are collected in a single tempo rary table named newaddr It contains columns for the customer number and the address related fields of the customer table Now the time comes to apply all the new addresses at once This idea of collecting routine changes in a Database Privileges separate table and applying them in a batch outside of peak hours is one of the performance techniques covered in Chapter 10 Tuning Your Data Model UPDATE customer SET addressl address2 city state zipcode SELECT addressl address2 city state zipcode FROM newaddr WHERE newaddr customer_num customer customer_num WHERE customer_num IN SELECT customer_num FROM newaddr Notice that the values for multiple columns are produced by a single SELECT statement If you rewrite this example in the other form with an assignment for each updated column you must write five SELECT statements one for each column to be updated Not only is such a statement harder to write it also takes much longer to execute Note In INFORMIX 4GL and the SQL API programs you can use record or host variables to update values For more information refer to Chapter 5 Programming with SQL Database Privileges Two levels of privileges exist in a database database level privileges and table level privileges When you cre
29. column data type max size typical catalog num SERIAL 4 4 stock_num SMALLINT 2 2 manu_code CHAR 3 3 3 cat_descr TEXT 56 56 cat_picture BYTE 56 56 cat_adv VARCHAR 255 65 256 66 typrow 191 homerow 191 typrow lt pageuse overpage 0 typrow lt pageuse homemax 381 maxrow lt pageuse datrows 8 floor pageuse homemax typrow datpages 625 ceiling estrows datrows expages 0 estrows x overpage Estimating the size of the catalog table Tuning Your Data Model 10 15 Calculating Table Sizes Estimating Index Pages The tblspace includes index pages as well as pages of data and index pages can be a significant fraction of the total An index entry consists of a key and a pointer The key is a copy of the indexed column or columns from one row of data The pointer is a 4 byte value used to locate the row containing that key value A unique index contains one such entry for every row in the table It also contains some additional pages of pointers that create the B tree structure Index structure is described in The Cost of Network Access on page 13 20 When an index allows duplicates it contains fewer keys than pointers that is one key can be followed by a list of pointers If this were the whole story on indexes it would be simple to estimate their space requirements However the index leaf pages use a technique called key compression which allows the database server to put more keys on a page than would
30. cursor as pointing to one row of the collection This situation is true as long as no other programs are modifying the same data concurrently Creating the Active Set When a cursor is opened the database server does whatever is necessary to locate the first row of selected data Depending on how the query is phrased this can be very easy to do or it can require a great deal of work and time DECLARE easy CURSOR FOR SELECT fname lname FROM customer WHERE state NJ Because this cursor queries only a single table in a simple way the database server can very quickly discover whether any rows satisfy the query and find the first one The first row is the only row it finds at this time The rest of the rows in the active set remain unknown DECLARE hard CURSOR FOR SELECT C customer_num O order_num sum items total_price FROM customer C orders O items I WHERE C customer_num O customer_num AND O order_num I order_num AND O paid_date is null GROUP BY C customer_num O order_num The active set of this cursor is generated by joining three tables and grouping the output rows The optimizer might be able to use indexes to produce the rows in the correct order but in general the use of ORDER BY or GROUP BY clauses requires the database server to generate all the rows copy them to a temporary table and sort the table before it can know which row to present first This is discussed in Chapter 13 Optimizin
31. erences the table from which it came The relationship between the name and faxname tables is one to many because one name can be associated with many fax numbers in the other direction each faxname combination can be associ ated with one rec_num The relationship between the fax and faxname tables is one to many because each number can be associated with many faxname combinations Building Your Data Model 8 27 Resolving Your Relationships name rec_num PK rec_num PK Iname Iname fname S fname bdate y bdate anniv y anniv email faxname email child1 fax num PK FK child1 child2 rec num PK FK O ichild2 child3 WW child3 fax fax_num PK fax rec_num FK ope om ar oper til oper_till BEFORE AFTER Figure 8 13 Resolving a many to many relationship Resolving Other Special Relationships You may encounter other special relationships that can hamper a smooth running database These relationships are shown in the following list Complex relationships Recursive relationships Redundant relationships A complex relationship is an association among three or more entities All the entities must be present for the relationship to exist To reduce this complex ity reclassify all complex relationships as an entity related through binary relationships to each of the original entities A recursive relationship is an association between occurrences of the same
32. in Condition segment 1 417S NOT 2 36T Index 27 28 Index OR 2 36T LOGN function syntax in expression 1 4525 use in expression 1 452S lok extension 1 370S Loo controlled 2 165 creating and exiting in SPL 14 23T exiting using RAISE exception 14 32T indefinite with WHILE 2 465 Loopback local 12 9T LOW keyword 1 374S M Machine notes Intro 9R Intro 11S 6T Mandatory entity in relationship 8 9T Many to many relationship 8 9T 8 11T 8 26T Mapping files for non standard code sets 5 5R MATCHES keyword syntax in Condition segment 1 405S use in Condition segment 1 409S in SELECT 1 328S with NLS 2 42T used to test for equality in WHERE clause 2 29T wildcard characters 1 329S MATCHES relational operator in WHERE clause 2 37T MAX function as aggregate function 2 53T syntax in expression 1 462S use in expression 1 464S MDY function as time function 2 56T syntax in expression 1 454S Memory allocating for a system sqlda structure 1 98 shared 12 7T Message files error messages Intro 9R Intro 115 7T setting LANG for NLS 4 49R specifying subdirectory for NLS 1 22R specifying subdirectory with DBLANG 4 19R MIN function as aggregate function 2 53T syntax in expression 1 462S use in expression 1 464S Minus sign arithmetic operator 1 431S MINUTE keyword syntax in DATETIME data type 1 428S in INTERVAL data type 1 485S use as DATETIME field qualifier 3 8R 1 488S as INTERVAL field qualifier 3 14R 1 491S Mir
33. in which the primary key is user id and the only other column contains a single character C R or D for the privilege level A grant to the keyword of PUBLIC is reflected as a user name of public lowercase Table level privileges are recorded in systabauth which uses a composite primary key of the table number grantor and grantee In the tabauth column the privileges are encoded in a six letter list as shown in the following diagram unconditional Update ii ae Index unconditional Select SU IdXar References Alter Delete if column privilege granted A hyphen means an ungranted privilege so that a grant of all privileges is shown as su idxar and u shows a grant of only Update The code letters are normally lowercase but they are uppercase when the keywords WITH GRANT OPTION are used in the GRANT statement When an asterisk appears in the third position some column level privilege exists for that table and grantee The specific privilege is recorded in sysco lauth Its primary key is a composite of the table number the grantor the grantee and the column number The only attribute is a three letter list showing the type of privilege s u or r You can grant the Index privilege to anyone but to exercise the ability the user must also hold the Resource database privilege So although the Index privilege is granted automatically except in ANSI compliant databases users who have only the Connec
34. might require updating of information in databases on differ ent database servers To maintain the integrity of the data it is essential that either all the different databases are updated or none of the databases are updated Two Phase Commit Two phase commit is a protocol that coordinates work performed at multiple database servers on behalf of a single transaction Unlike the data replication and archiving tools discussed earlier in this section two phase commit does not make two copies of the data It protects the validity of one transaction 12 20 Understanding Informix Networking Summary Summary which involves several different databases that may or may not be ona network Because two phase commit involves only one transaction it is not usually classed as data protection A transaction that involves multiple database servers is called a global transaction Two phase commit is a natural extension of transaction handling which is discussed in Interrupted Modifications on page 4 22 The INFORMIX OnLine Dynamic Server Administrator s Guide discusses two phase commit in detail The two phase commit begins when a user process has completed all of its work and requests a commit of the global transaction Phase 1 The current database server asks each participating database server if it can commit its local transactions Each database server responds Yes or No Phase 2 If all the database servers res
35. p_city p_state p_zip 6 items END PROCEDURE DOCUMENT This procedure takes the last name of a customer as brief description its only argument It returns the full name and address of the customer WITH LISTING IN acctng test listfile compile time warnings go here end of the procedure read_address Procedure that reads from the customer table Creating a Procedure Using an SQL API To create a stored procedure using an SQL API put the text of the CREATE PROCEDURE statement in a file Use the CREATE PROCEDURE FROM state ment and refer to that file to compile the procedure For example to create a procedure to read a customer name you can use a statement such as the one in Figure 14 1 and store it in a file If the file is named read_add_source the following statement compiles the read_address procedure CREATE PROCEDURE FROM read_add_source Creating and Using Stored Procedures 14 5 Creating and Using Stored Procedures Figure 14 2 shows how the previous SQL statement looks in an ESQL C program This program creates whatever procedure is in the file read_add_source f include lt stdio h gt Sinclude sqlca Sinclude sqlda include datetime Program to create a procedure from the pwd main Sdatabase play Screate procedure from read_add_source Figure 14 2 SQL statement that compiles and stores the read_address procedure in an ESQL C p
36. setting the INFORMIXCONTIME environment variable 4 35R Connectivity in relationship 8 8T 8 11T 8 17T Constant expression in SELECT 1 314S inserting with PUT 1 286S restrictions with GROUP BY 1 334S syntax 1 436S See also Expression segment See also Literal Number Constraint adding with ALTER TABLE 1 298 1 865 cardinality 8 9T checking 1 131S defining domains 9 3T definition of 1 85S dropping with ALTER TABLE 1 325 1 865 enforcing 1 86S modifying a column that has constraints 1 27S number of columns allowed 1 86S 1 925 optimizer uses 13 9T privileges needed to create 1 31S rules for unique constraints 1 30S setting checking mode 1 349S specifying at table level 1 925 with DROP INDEX 1 1745 See also Primary key constraint See also Referential constraint See also Unique constraint CONSTRAINT keyword in ALTER TABLE 1 298 in CREATE TABLE 1 918 Contention for bottleneck tables 10 35T for disk access arms 10 7T reducing 10 32T 10 35T CONTINUE keyword in the WHENEVER statement 1 398S 1 402S CONTINUE statement exiting a loop 14 23T syntax 2 6S Conventions example code Intro 8R Intro 10S 5T for naming tables 1 845 syntax Intro 5S typographical Intro 5R Intro 5S 5T Converting data types 3 23R Coordinated deletes 6 6T Correlated subquery definition of 1 413S 3 32T restriction with cascading deletes 4 22T Correlation name and stored procedures 1 125S in COUNT DISTINCT clause 1 125S in DELETE REFERENCING c
37. statements to be the last and first ones respectively so that the entire scan over the master table is one large transaction This is sometimes possible but it may become impractical if many rows need to be updated The number of locks can be too large and they are held for the duration of the program 7 18 Programming for a Multiuser Environment Summary Summary A solution supported by Informix database servers is to add the keywords WITH HOLD to the declaration of the master cursor Such a cursor is referred to as a hold cursor and is not closed at the end of a transaction The database server still closes all other cursors and it still releases all locks but the hold cursor remains open until it is explicitly closed Before you attempt to use a hold cursor you must be sure that you understand the locking mechanism described here and you must also under stand the programs that are running concurrently The reason is that when ever COMMIT WORK is executed all locks are released including any locks placed on rows fetched through the hold cursor This has little importance if the cursor is used as intended for a single forward scan over a table However you are allowed to specify WITH HOLD for any cursor including update cursors and scroll cursors Before you do this you must understand the implications of the fact that all locks including locks on entire tables are released at the end of a transaction Whenever multipl
38. tblspace includes pages allocated to data rows of that table and pages allo cated to indexes It also includes pages used by blob columns that are located in the tblspace but not pages used by blob data in a separate blobspace or blob data stored on an optical storage subsystem This choice is discussed under Locating Blob Data on page 10 18 The tblspace is an accounting entity only it does not correspond to any particular part of a dbspace The indexes and data extents that make up a table can be scattered throughout the dbspace Tuning Your Data Model 10 7 INFORMIX OnLine Dynamic Server Disk Storage The oncheck utility with the pt option returns information on the status of tblspaces including the counts of pages allocated and in use for each one You can use this information to monitor the growth of a table over time Extents As you add rows to a table OnLine allocates disk space to it in units called extents Each extent is a block of physically contiguous pages from the dbspace Even when the dbspace comprises more than one chunk extents are always allocated entirely within a single chunk to remain contiguous Contiguity is important to performance When the pages of data are contiguous disk arm motion is minimized when the database server reads the rows sequentially The mechanism of extents is a compromise between the following competing requirements Most dbspaces are shared among several tables e The
39. variable 4 14R ON Archive utility using the ARC_KEYPAD environment variable 4 15R oncheck utility 10 7T 10 12T 13 31T ONCONFIG environment variable 4 39R onconfig file specifying with ONCONFIG 4 40R One to many relationship 8 9T 8 11T One to one relationship 8 9T 8 11T OnLine 5 10T On line files Intro 8R Intro 11S 6T help Intro 9R Intro 11S 7T onload utility 4 27T 10 11T onstat utility 10 12T onunload utility 4 27T 10 11T OPEN statement activating a cursor 5 20T constructing the active set 1 264S opening a procedure cursor 1 265S opening an insert cursor 1 266S opening select or update cursors 1 2645 5 20T reopening a cursor 1 2675 substituting values for parameters 1 268S syntax 1 263S with concatenation operator 1 432S with FREE 1 269S Opening a cursor 5 20T 5 24T Operating system DOS 12 4T UNIX 12 4T Optical device 12 6T Optimization specifying a high or low level 1 374S Optimizer and GROUP BY 13 10T 13 12T 13 27T and ORDER BY 13 10T 13 12T 13 27T and SET OPTIMIZATION statement 1 3745 13 36T autoindex path 13 29T composite index use 13 31T data distributions 13 29T disk access 13 14T display query plan 13 12T filter selectivity 13 30T index not used by 13 32T 13 35T index used by 13 9T 13 10T methods of 13 8T query plan 13 22T sort merge join 13 27T sorting 13 12T specifying high or low level of optimization 13 36T system catalog use 13 9T when index not used 13 33T with UPDATE STATI
40. which deletes rows from the customer table using a WHERE clause with the customer_num provided by the user CREATE DBA PROCEDURE delete_customer cnum INT DELETE FROM customer WHERE customer_num cnum END PROCEDURE Stored procedure to delete a row Monitoring Changes to Data Using stored procedures you can create a record of changes made to a database You can record changes made by a particular user or you can make a record of each time a change is made You can monitor all the changes made to the database by a single user Simply channel all changes through stored procedures that keep track of changes made by each user If you want to record each time the user acctclrk modifies the database set up the database with the following privileges e You are the DBA of the database e All other users have the Connect privilege to the database They may or may not have the Resource privilege They do not have the Delete for this example privilege on the table being protected e Your stored procedure is created using the DBA keyword e Your stored procedure performs the deletion and records that a change has been made by a certain user Granting and Limiting Access to Your Database 11 17 Controlling Access to Data Using Stored Procedures Write a stored procedure similar to the one in Figure 11 6 which updates a table using a customer number provided by the user If the user happens to be acctclrk a record of
41. x masks the original variable x After the END statement which marks the end of the nested block the original value of x is accessible again CREATE PROCEDURE scope DEFINE x y z INT LET x 5 LET y 10 LET z x yj z is 15 BEGIN DEFINE x q INT DEFINE z CHAR 5 LET x 100 LET q x y q 110 LET z silly z receives a character value END LET y x y is now 5 LET x z z is now 15 not silly END PROCEDURE Figure 14 9 Masking of variables with nested statement blocks Variable Keyword Ambiguity If you define a variable as a keyword ambiguities can occur The following rules for identifiers help you avoid ambiguities for variables procedure names and system function names Defined variables take the highest precedence e Procedures defined as such in a DEFINE statement take precedence over SQL functions SQL functions take precedence over procedures that exist but are not identified as procedures in a DEFINE statement In some cases you must change the name of the variable For example you cannot define a variable with the name count or max because these are the names of aggregate functions Refer to Chapter 1 of the Informix Guide to SQL Syntax for a list of the keywords that can be used ambiguously Variables and Column Names If you use the same identifier for a procedural variable as you use for a col umn name the database server assumes that eac
42. 0x0000001 0x0000007D 0x00000857 0x0000001 Ox0000007E 0x0001395B 0x0000001 Ox0000007F 0x0000EBF6 0x0000001 0x00000080 0x00014C10 0x0000001 Oo Ay SA ow Fl Ry E Ry QAWPODAIDGUOBWNFO Query Result 2 68 2 66 Composing Simple SELECT Statements Single Table SELECT Statements Using Stored Procedures in SELECT Statements We have seen examples of SELECT statement expressions consisting of column names operators and functions Another type of expression is one that contains a stored procedure call Stored procedures are procedures that contain special Stored Procedure Language SPL statements as well as SQL statements For more information on stored procedures refer to Chapter 14 Creating and Using Stored Proce dures Stored procedures provide a way to extend the range of functions available you can perform a subquery on each row you select For example suppose you want a listing of the customer number the customer s last name and the number of orders the customer has made One way to retrieve this information is shown in Query 2 69 The customer table has customer_num and Iname columns but no record of the number of orders each customer has made You could write a get_orders procedure which queries the orders table for each customer_num and returns the number of corresponding orders labeled n_orders SELECT customer_num lname get_orders customer_num n_orders FROM
43. 1 126 00 746 Too many items for Mfr Error number 746 with user specified message text If you invoke the trigger through an SQL statement in an SQL API the database server sets sqlcode to 746 and returns the message text in the sqlerrm field of the SQL Communications Area SQLCA See Chapter 5 Pro gramming with SQL for your SQL API for a description of the SQLCA In introducing triggers this chapter explains the following topics e The purpose of each component of the CREATE TRIGGER statement e How to create BEFORE and AFTER triggered actions and how to use them to determine the impact of the triggering statement e How to create a FOR EACH ROW triggered action and how to use the REFERENCING clause to refer to the values of columns both before and after the action of the triggering statement e The advantages of using stored procedures as triggered actions e How to trace triggered actions if they are behaving unexpectedly e How to generate two types of error messages within a triggered action Creating and Using Triggers 15 17 Summary 15 18 Creating and Using Triggers Index This index covers the Tutorial Reference and Syntax manuals Page numbers that end in T can be found in the Tutorial those that end in R can be found in the Reference Manual and those that end in S can be found in the Syntax manual Special symbols are listed in ASCII order at the end of the index A ABS function syn
44. 1 396S examining index pages 1 394S optimizing search strategies 1 3945 syntax 1 392S using the LOW keyword 1 395S when to execute 1 395S Update trigger defining multiple 1 114S USER function as affected by ANSI compliance 1 2315 1 300S 1 438S syntax in Condition segment 1 405S in expression 1 436S in INSERT 1 250S use in ALTER TABLE 1 188 in CREATE TABLE 1 888 in expression 1 438S 2 63T 2 64T 3 19T in INSERT 1 252S User informix privileges associated with 1 2345 Using correlation names 1 1245 USING DESCRIPTOR keywords information from DESCRIBE 1 164S syntax in EXECUTE 1 1845 in FETCH 1 1945 in OPEN 1 263S in PUT 1 2845 use in FETCH 1 2015 in OPEN 1 269S in PUT 1 1885 1 2885 1 289S USING keyword syntax in EXECUTE 1 186S in OPEN 1 263S use in EXECUTE 1 1868 5 31T in OPEN 1 268S USING SQL DESCRIPTOR keywords in DESCRIBE 1 164S in EXECUTE 1 1875 Utility program chkenv 5 4R crtcmap 5 5R dbexport 5 8R dbimport 5 13R dbload 5 19R 9 28T 10 12T dbschema 5 33R 9 26T oncheck 10 7T 10 12T onload 4 27T 10 11T onstat 10 12T onunload 4 27T 10 11T V VALUE clause after NULL value is fetched 1 215S relation to FETCH 1 214S use in GET DESCRIPTOR 1 212S use in SET DESCRIPTOR 1 355S VALUES clause effect with PUT 1 286S syntax in INSERT 1 245S use in INSERT 1 250S 4 7T VARCHAR data type considerations for UNLOAD statement 1 379S description of 3 22R 9 15T effect on table size 10 14T requirem
45. 10 and orders it by manu_code The results are shown in Query Result 3 40 stock_num manu_code ANZ ANZ ANZ HSK HSK NKL 5 NRG 106 PRC 113 SHM wU hI e OLN 20 Query Result 3 40 3 48 Composing Advanced SELECT Statements Set Operations See Chapter 1 of the Informix Guide to SQL Syntax for the complete syntax of the SELECT statement and the UNION operator See also Chapter 5 Pro gramming with SQL and Chapter 6 Modifying Data Through SQL Programs as well as the product manuals for information specific to the INFORMIX 4GL and INFORMIX ESQL C products and any limitations involving the INTO clause and compound queries Query 3 41 uses a combined query to select data into a temporary table and then adds a simple query to order and display it You must separate the combined and simple queries with a semicolon The combined query uses a literal in the select list to tag the output of part of a union so it can be distinguished later The tag is given the label sortkey The simple query uses that tag as a sort key for ordering the retrieved rows SELECT 1 sortkey lname fname company city state phone FROM customer x WHERE state CA UNION SELECT 2 sortkey lname fname company city state phone FROM customer y WHERE state lt gt CA INTO TEMP calcust SELECT FROM calcust ORDER BY 1 Query 3 41 Composing Advanced SELECT Statements 3 49 Set Operations
46. 1012 278701 06 18 1993 104 1013 B77930 06 22 1993 106 1014 8052 06 25 1993 110 1015 MAOO3 06 27 1993 119 1016 PC6782 06 29 1993 120 1017 DM354331 07 09 1993 121 1018 S22942 07 10 1993 122 1019 255709 07 11 1993 123 1020 W2286 07 11 1993 124 1021 C3288 07 23 1993 126 1022 w9925 07 24 1993 127 1023 KF2961 07 24 1993 Query Result 2 17 2 24 Composing Simple SELECT Statements Single Table SELECT Statements You can include the DESC keyword in the ORDER BY clause when you assign integers to column names as shown in Query 2 18 SELECT customer_num order_num po_num order_date FROM orders ORDER BY 4 DESC 1 Query 2 18 In this case data is first sorted in descending order by order_date and in ascending order by customer_num ORDER BY and Native Language Support You can set the DBNLS environment variable to activate Native Language Support NLS functionality You can then specify a language environment locale by setting the LANG environment variable and can set the LC_COLLATE X Open category to further define the collation order Query 2 18 uses a SELECT statement with an ORDER BY clause on a column containing data of type NCHAR the NLS equivalent of CHAR This NLS table abonn s is provided separately from the demonstration database this SELECT statement example is provided as the sel_nls1 sql command file with NLS enabled DB Access SELECT num ro nom pr nom FROM abonn s ORDER BY nom Qu
47. 11 6 You need the other table level privileges to modify data The owners of tables often withhold these privileges or grant them only to specific users As a result you may not be able to modify some tables that you can query freely Because these privileges are granted on a table by table basis you can have only Insert privileges on one table and only Update privileges on another for example The Update privileges can be restricted even further to specific columns in a table Chapter 11 Granting and Limiting Access to Your Database discusses granting privileges from the standpoint of the DBA A complete list of privi leges and asummary of the GRANT and REVOKE statements can be found in Chapter 1 of the Informix Guide to SQL Syntax Displaying Table Privileges 4 16 Modifying Data If you are the owner of a table that is if you created it you have all privileges on that table Otherwise you can determine the privileges you have for a certain table by querying the system catalog The system catalog consists of system tables that describe the database structure The privileges granted on each table are recorded in the systabauth system table To display these privileges you must also know the unique identifier number of the table This number is specified in the systables system table So to display privileges granted on the orders table you might enter the following SELECT statement SELECT FROM systabauth WHERE
48. 3 Introducing the SELECT Statement 4 Some Basic Concepts 4 Privileges 5 Relational Operations 5 Selection and Projection 5 Joining 8 The Forms of SELECT 10 Special Data Types 11 Single Table SELECT Statements 11 Selecting All Columns and Rows 12 Using the Asterisk 12 Reordering the Columns 13 Sorting the Rows 13 Selecting SpecificColumns 18 ORDER BY and Native Language Support 25 Selecting Substrings 27 Using the WHERE Clause 28 Creating a Comparison Condition 29 Using Variable Text Searches 37 Using Exact Text Comparisons 37 Using a Single Character Wildcard 38 MATCHES and Native Language Support 42 Comparing for Special Characters 43 Expressions and Derived Values 46 Arithmetic Expressions 46 Sorting on Derived Columns 52 Using Functions in SELECT Statements 53 Aggregate Functions 53 Time Functions 56 Other Functions and Keywords 63 Using Stored Procedures in SELECT Statements 67 Multiple Table SELECT Statements 69 Creating a Cartesian Product 69 Creating aJoin 71 Equi Join 71 Natural Join 75 Multiple Table Join 77 Some Query Shortcuts 79 Using Aliases 79 The INTO TEMP Clause 83 Summary 84 2 2 Composing Simple SELECT Statements Chapter Overview SELECT is the most important and the most complex SQL statement It is used along with the SQL statements INSERT UPDATE and DELETE to manipulate data You can use the SELECT statement in the following ways e By itself to retrieve data from a database
49. 3 32a finds at least one row SELECT UNIQUE manu_name lead_time FROM manufact WHERE EXISTS SELECT FROM stock WHERE description MATCHES shoe AND manufact manu_code stock manu_code Query 3 32a 3 38 Composing Advanced SELECT Statements Subqueries in SELECT Statements You often can construct a query with EXISTS that is equivalent to one that uses IN You also can substitute ANY for IN as shown in Query 3 32b SELECT UNIQUE manu_name lead_time FROM stock manufact WHERE manufact manu_code IN SELECT manu_code FROM stock WHERE description MATCHES shoe AND stock manu_code manufact manu_code Query 3 32b Query 3 32a and Query 3 32b return rows for the manufacturers that produce a kind of shoe as well as the lead time for ordering the product These results are shown in Query Result 3 32 manu_name lead_time Anza 5 Hero 4 Karsten 21 Nikolus 8 ProCycle 9 Shimara 30 Query Result 3 32 Note that you cannot use the predicate IN for a subquery that contains a column with a TEXT or BYTE data type Add the keyword NOT to IN or to EXISTS to create a search condition that is the opposite of the one in the preceding queries You also can substitute ALL for NOT IN Query 3 33 shows two ways to do the same thing One way might allow the database server to do less work than the other depending on the design of the database and the size of the tables To find out which query might be
50. 32 511 yes bytes no CHAR n Length exceeds 255 yes bytes no TEXT BYTE VARCHAR m Figure 9 1 9 6 Implementing Your Data Model A diagram of the decisions to be made in choosing a data type 2 of 2 Defining the Domains Numeric Types Informix database servers support eight numeric data types Some are best suited for counters and codes some for engineering quantities and some for money Counters and Codes INTEGER and SMALLINT The INTEGER and SMALLINT data types hold small whole numbers They are suited for columns that contain counts sequence numbers numeric identity codes or any range of whole numbers when you know in advance the maximum and minimum values to be stored Both types are stored as signed binary integers INTEGER values have 32 bits and can represent whole numbers from 1 through poly that is from 2 147 483 647 through 2 147 483 647 The maximum negative number 2 147 483 248 is reserved and cannot be used SMALLINT values have only 16 bits They can represent whole numbers from 32 767 through 32 767 The maximum negative number 32 768 is reserved and cannot be used These data types have the following advantages e They take up little space 2 bytes per value for SMALLINT and 4 bytes per value for INTEGER e Arithmetic expressions such as SUM and MAX as well as sort comparisons can be done very efficiently on them The disadvantage to using INTEGER and SMALLINT is the li
51. 511 In NLS mode the NCHAR n data type con tains a sequence of n native characters with the same length range as CHAR Whenever a CHAR n or NCHAR 1 value is retrieved or stored exactly n bytes are transferred If an inserted value is short it is extended with spaces to make up n bytes A value longer than n is truncated No provision exists for variable length data in this format A CHAR n or NCHAR n value can include tabs and spaces but normally contains no other nonprinting characters When rows are inserted using INSERT or UPDATE or when rows are loaded with a utility program no means exists for entering nonprintable characters However when rows are created by a program using embedded SQL the program can insert any char acter except the null binary zero character It is not a good idea to store non printable characters in a character column because standard programs and utilities do not expect them The advantage of the CHAR or NCHAR n data type is that it is available on all database servers The only disadvantage of CHAR n or NCHAR n is that its length is fixed When the length of data values varies widely from row to row space is wasted NCHAR n is available on all database servers when NLS has been enabled Variable Length Strings VARCHAR m r and NVARCHAR m r Often the items in a character column have different lengths that is many have an average length and only a few have the maximum length The VARCHA
52. 7 13T locks released at end of transaction 7 18T mode 1 5R overriding row level 1 261S releasing with COMMIT WORK 1 43S releasing with ROLLBACK WORK 1 306S scope 1 5R 7 6T scope of lock 7 6T setting lock mode 7 13T shared locks 1 6R types of locks database lock 7 6T exclusive lock 7 6T key lock 7 8T page lock 1 108S 7 8T promotable lock 7 6T 7 9T row lock 1 108S 7 8T shared lock 7 6T table lock 7 7T update cursors effect on 1 152S update locks 1 385S waiting period 1 370S with DELETE 6 4T FETCH 1 201S scroll cursor 1 369S SET ISOLATION 1 366S SET LOCK MODE 1 370S UNLOCK TABLE 1 381S update cursor 7 9T within transaction 1 35S See also Table locking LOG IN keywords syntax in CREATE DATABASE 1 575 LOG10 function syntax in expression 1 452S use in expression 1 4525 Logarithmic function syntax LOG10 function 1 451S LOGN function 1 451S use LOG10 function 1 452S LOGN function 1 452S Loggin buffered 9 22T buffered vs unbuffered 1 372S cascading deletes 1 245 1 985 changing mode with SET LOG 1 372S choosing for OnLine database server 9 22T choosing for SE database server 9 23T finding log file location 1 60S renaming log 1 377S setting with CREATE TABLE 1 104S starting with START DATABASE 1 605 1 376S stopping 1 377S stopping with START DATABASE 1 376S unbuffered 9 22T with INFORMIX OnLine 1 595 with INFORMIX SE 1 60S with triggers 1 1345 Logical log definition of 4 25T Logical operator AND 2 36T
53. Composing Advanced SELECT Statements 3 39 Subqueries in SELECT Statements better you can use the SET EXPLAIN command to get a listing of the query plan SET EXPLAIN is discussed in Chapter 13 Optimizing Your Queries of this manual and in Chapter 1 of the SELECT customer_num company WHERE customer_num NOT IN SELECT customer_num SELECT customer_num company Informix Guide to SQL Syntax FROM customer FROM orders WHERE customer customer_num orders customer_num FROM customer WHERE NOT EXISTS SELECT FROM orders WHERE customer customer_num orders customer_num Query 3 33 Each statement in Query 3 33 returns the rows shown in Query Result 3 33 which identify customers who have not placed orders customer_num company 102 103 105 107 108 109 113 114 118 125 128 Sports Spot Phil s Sports Sport Stuff Sportstown Total Fitness Query Result 3 33 Note that the keywords EXISTS and Los Altos Sports Athletic Supplies Quinn s Sports Sporting Place Blue Ribbon Sports Sports Phoenix University IN are used for the set operation known as intersection and the keywords NOT EXISTS and NOT IN are used for the set operation known as difference These concepts are discussed in Set Opera tions on page 3 42 3 40 Composing Advanced SELECT Statements Subqueries in SELECT Statements Query 3 34 identifies all the items in the stock table that have not be
54. Composing Simple SELECT Statements 2 43 Single Table SELECT Statements can search for occurrences of a percent sign in the res_descr column with the LIKE wildcard The query retrieves the row shown in Query Result 2 35 customer_num 116 call_dtime 1992 12 21 11 24 user_id mannyn call_code T call_descr Second complaint from this customer Received two cases right handed outfielder gloves 1 HRO instead of one case lefties res_dtime 1992 12 27 08 19 res_descr Memo to shipping Ava Brown to send case of left handed gloves pick up wrong case memo to billing requesting 5 discount to placate customer due to second offense and lateness of resolution because of holiday Query Result 2 35 Using Subscripting in a WHERE Clause You can use subscripting in the WHERE clause of a SELECT statement to specify a range of characters or numbers in a column as shown in Query 2 36 SELECT catalog_num stock_num manu_code cat_advert cat_descr FROM catalog WHERE cat_advert 1 4 High Query 2 36 The subscript 1 4 causes Query 2 36 to retrieve all rows in which the first four letters of the cat_advert column are High as shown in Query Result 2 36 2 44 Composing Simple SELECT Statements Single Table SELECT Statements catalog_num 10004 stock_num 2 manu_code HRO cat_advert Highest Quality Ball Available from Hand Stitching to the Robinson Signature cat_descr Jackie Robinson signature ball Highes
55. EACH ROW Triggered Actions 8 Using the REFERENCING Clause 9 Using the WHEN Condition 10 Using Stored Procedures as Triggered Actions 10 Passing Data to a Stored Procedure 11 Using the SPL 11 Updating Nontriggering Columns with Data froma Stored Procedure 12 Tracing Triggered Actions 12 Generating Error Messages 14 Applying a Fixed Error Message 15 Generating a Variable Error Message 16 Summary 17 15 2 Creating and Using Triggers Chapter Overview An SQL trigger is a mechanism that resides in the database It is available to any user who has permission to use it It specifies that when a particular action an insert a delete or an update occurs on a particular table the database server should automatically perform one or more additional actions The additional actions can be INSERT DELETE UPDATE or EXECUTE PROCEDURE statements This chapter describes the purpose of each component of the CREATE TRIGGER statement illustrates some uses for triggers and describes the advantages of using a stored procedure as a triggered action When to Use Triggers Because a trigger resides in the database and anyone who has the required privilege can use it a trigger enables you to write a set of SQL statements that multiple applications can use It enables you to prevent redundant code when multiple programs need to perform the same database operation Among other uses you can use triggers to perform the following actions e Cre
56. For example an order for a nonexistent product could be entered into the orders table Or a customer with outstanding orders could be deleted from the customer table Or the order number could be updated in the orders table and not in the items table In each of these cases the integrity of the stored data is lost Data integrity is actually made up of three parts e Entity integrity Each row of a table has a unique identifier Semantic integrity The data in the columns properly reflects the types of information the column was designed to hold Modifying Data 4 17 Data Integrity Referential integrity The relationships between tables are enforced Well designed databases incorporate these principles so that when you modify data the database itself prevents you from doing anything that might harm the data integrity Entity Integrity An entity is any person place or thing to be recorded in a database Each entity represents a table and each row ofa table represents an instance of that entity For example if order is an entity the orders table represents the idea of order and each row in the table represents a specific order To identify each row in a table the table must have a primary key The primary key is a unique value that identifies each row This requirement is called the entity integrity constraint For example the orders table primary key is order_num The order_num column holds a unique system generat
57. INTO Clause 22 Cursor Input Modes 23 The Active Set ofa Cursor 24 Creating the Active Set 24 The Active Set for a Sequential Cursor 25 The Active Set for a Scroll Cursor 25 The Active Set and Concurrency 25 Using a Cursor A Parts Explosion 26 Dynamic SQL 28 Preparing a Statement 29 Executing Prepared SQL 31 Using Prepared SELECT Statements 31 Dynamic Host Variables 32 Freeing Prepared Statements 33 Quick Execution 34 Embedding Data Definition Statements 34 Embedding Grant and Revoke Privileges 34 Summary 37 5 2 Programming with SQL Chapter Overview In the examples in the previous chapters SQL is treated as if it were an interactive computer language that is as if you could type a SELECT statement directly into the database server and see rows of data rolling back to you Of course that is not how things are Many layers of software stand between you and the database server The database server retains data in a binary form that must be formatted before it can be displayed It does not return a mass of data at once it returns one row at a time asa program requests it You can access information in your database in two ways through interactive access using DB Access or INFORMIX SQL or through application programs written using an SQL API Almost any program can contain SQL statements execute them and retrieve data from a database server This chapter explains how these activities are performed and indicates how you can
58. KF 2961 LZ230 A003 PC6782 Q13557 S22942 W2286 w9925 Z55709 Query Result 2 15 To select multiple columns from a table list them in the select list in the SELECT clause Query 2 16 shows the order in which the columns are selected is the order in which they are produced from left to right SELECT paid_date ship_date order_date customer_num order_num po_num FROM orders ORDER BY paid_date order_date customer_num Query 2 16 2 22 Composing Simple SELECT Statements Single Table SELECT Statements As shown in Sorting on Multiple Columns on page 2 15 you can use the ORDER BY clause to sort the data in ascending or descending order and perform nested sorts Query Result 2 16 shows descending order paid_date 06 03 06 14 06 21 07 10 07 21 07 22 07 31 08 06 08 06 08 21 08 22 08 22 08 22 08 29 08 31 09 02 09 20 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 ship_date 05 30 06 05 06 29 07 12 07 13 05 26 05 23 06 09 07 03 07 06 06 01 07 10 07 13 07 16 06 21 06 29 07 25 07 30 07 03 07 16 07 30 07 16 Query Result 2 16 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 order_date customer_num order_num 05 22 05 30 05 31 06 18 06 29 07 09 05 21 05 22 05 24 06 25 06 07 05 20 06 22 07 07 06 06
59. No matter what access controls the operating system gives you when the contents of an entire database are highly sensitive you might not want to leave it on a public disk fixed to the machine You can circumvent normal software controls when the data must be secure When the database is not being used by you or another authorized person it does not have to be available on line You can make it inaccessible in one of the following ways which have varying degrees of inconvenience Detach the physical medium from the machine and take it away If the disk itself is not removable the disk drive might be removable Copy the database directory to tape and take possession of the tape Copy the database files using an encryption utility Keep only the encrypted version In the latter two cases after making the copies you must remember to erase the original database files using a program that overwrites an erased file with null data Instead of removing the entire database directory you can copy and then erase the files that represent individual tables However do not overlook the fact that index files contain copies of the data from the indexed column or columns Remove and erase the index files as well as the table files Granting Privileges The authorization to use a database is called a privilege For example the authorization to use a database at all is called the Connect privilege and the authorization to insert a row in
60. OnLine Dynamic Server you can simply select the data you want from the other database on another database server as part of an INSERT statement in your database As shown in the following example you could select information from the items table in the stores6 database to insert into a new table INSERT INTO newtable SELECT item_num order_num quantity stock_num manu_code total_price FROM stores6 otherserver items Implementing Your Data Model 9 27 Creating the Database If you are using INFORMIX SE you can select the data you want from one database and insert it into another database as long as the databases are on the same database server As shown in the following example you could select information from the catalog table in the stores6 database to insert into a new table by using a temporary table CONNECT TO sharky db1 SELECT catalog_num stock_num manu_code FROM catalog INTO temptable DISCONNECT CONNECT TO sharky db2 SELECT from temptable INTO newsetable If you want to select data from another database server in INFORMIX SE you must export the data to a file You can use the UNLOAD statement in DB Access INFORMIX SQL or INFORMIX 4GL or you can write a report in ACE or INFORMIX 4GL and direct the output to a file When the source is another kind of file or database you must find a way to convert it into a flat ASCII file that is a file of printable data in which each line rep
61. Prentice Hall 1988 Optimizing Your Queries 13 39 Making Queries Faster DISK PAGES 5 000 10 000 15 000 20 000 25 000 30 000 35 000 40 000 45 000 50 000 Sequential and Nonsequential Disk Access part 400 Pages 20 000 pages parven 30 000 pages vendor Disk Access Using Temporary Tables pv_by_vn 300 pages pvvn by pn 892 pages final query 590 pages Figure 13 8 Breaking a query into three steps using temporary tables The first step is to get the data of the parven table in vendor_num order as shown in the following example SELECT part_num vendor_num price FROM parven ORDER BY vendor_num INTO TEMP pv_by_vn This statement reads parven sequentially 50 pages writes a temporary table 50 pages and sorts it The cost of the sort assuming one merge level is about 200 pages for a total of 300 Join this temporary table to vendor and put the result in another temporary table ordered by part_num as shown in the following example SELECT pv_by_vn vendor vendor_name FROM pv_by_vn vendor WHERE pv_by_vn vendor_num vendor vendor_num ORDER BY pv_by_vn part_num INTO TEMP pvvn_by_pn DROP TABLE pv_by_vn 13 40 Optimizing Your Queries Summary Summary This query reads pv_by_vn sequentially 50 pages It accesses vendor by way of its index 15 000 times but as the keys are presented in vendor_num sequence the effect is to read vendor sequentially through its index 42 pages If
62. See Transaction manager TRACE command output from 15 14T TRACE statement debugging a stored procedure 14 11T syntax 2 425 Transaction and CREATE DATABASE 1 60S ANSI compliant database effects 1 11R committing with COMMIT WORK 1 43S cursors closed at end 7 18T description of 4 22T example with DELETE 6 5T global 12 21T locks held to end of 7 9T locks released at end 7 8T 7 18T logging 1 376S recovering transactions 1 308S Index 45 46 Index rolling back 1 4R 1 306S scroll cursor and data consistency 1 369S starting with BEGIN WORK 1 35S stopping logging 1 376S transaction log 4 24T 4 26T transaction log required 9 22T use signalled in SQLAWARN 5 12T using cursors in 1 155S Transaction logging ANSI compliant database effects 1 12R buffered 9 22T effect on database server type 1 5R establishing with CREATE DATABASE 9 21T OnLine methods of 9 22T renaming log 1 377S stopping 1 377S turning off for faster loading 9 28T turning off not possible 9 24T Transaction log contents of 4 25T Transaction manager 12 11T Transfer of database files 5 19R Transitive dependency 8 32T Trigger creating 15 4T definition of 15 3T in client server environment 1 133S number on a table 1 112S preventing overriding 1 132S when to use 15 3T Trigger event definition of 1 111S 15 5T example of 15 5T in CREATE TRIGGER statement 1 1115 INSERT 1 119S privileges on 1 113S with cursor statement 1 112S Trigger name assigning 15 5T sy
63. The location information for the database server is in the sqlhosts file Refer to Connection Information on page 12 15 The complete syntax for the CONNECT and DATABASE statements is covered in Chapter 1 of the Informix Guide to SQL Syntax Accessing Tables The database that is opened by a CONNECT DATABASE or CREATE DATABASE statement is the current database If you are using INFORMIX OnLine Dynamic Server you can query tables that are not in the current database To refer to a table in a database other than the current data base include the database name as part of the table name as illustrated in the following SELECT statement SELECT name number FROM salesdb contacts 12 16 Understanding Informix Networking Accessing Tables The database is salesdb The table in salesdb is named contacts You can use the same notation in a join When you must specify the database name explic itly the long table names can become cumbersome unless you use aliases to shorten them This is shown in the following example SELECT C custname S phone FROM salesdb contacts C stores customer S WHERE C custname S company To specify a table in a database that is managed by a different INFORMIX OnLine Dynamic Server database server you must qualify the database name with a database server name For example the following SELECT statement refers to table customer from database masterdb which resides on the database ser
64. Transaction Logging 5 Coordinated Deletions 6 Deleting with a Cursor 7 Using INSERT 8 Using an Insert Cursor 8 Declaring an Insert Cursor 9 Inserting with a Cursor 10 Status Codes After PUT and FLUSH 11 Rows of Constants 11 An Insert Example 12 Using UPDATE 14 Using an Update Cursor 15 The Purpose of the Keyword UPDATE 15 Updating SpecificColumns 16 UPDATE Keyword Not Always Needed 16 Cleaning up a Table 16 Summary 17 6 2 Modifying Data Through SQL Programs Chapter Overview The preceding chapter introduced the idea of putting SQL statements especially the SELECT statement into programs written in other languages This enables a program to retrieve rows of data from a database This chapter covers the issues that arise when a program needs to modify the database by deleting inserting or updating rows As in Chapter 5 Pro gramming with SQL this chapter aims to prepare you for reading the manual for the Informix ESQL or 4GL product you are using The general use of the INSERT UPDATE and DELETE statements is covered in Chapter 4 Modifying Data This chapter examines their use from within a program It is quite easy to put the statements in a program but it can be quite difficult to handle errors and to deal with concurrent modifications from multiple programs Using DELETE A program deletes rows from a table by executing a DELETE statement The DELETE statement can specify rows in the usual way with a
65. Valued Subqueries 36 Correlated Subqueries 37 Using EXISTS 38 Set Operations 42 Union 43 Intersection 51 Difference 53 Summary 54 3 2 Composing Advanced SELECT Statements Chapter Overview Chapter 2 Composing Simple SELECT Statements demonstrated some of the basic ways to retrieve data from a relational database with the SELECT statement This chapter increases the scope of what you can do with this pow erful SQL statement and enables you to perform more complex database queries and data manipulation Whereas the previous chapter focused on five of the clauses in SELECT statement syntax this chapter adds two more You can use the GROUP BY clause with aggregate functions to organize rows returned by the FROM clause You can include a HAVING clause to place conditions on the values returned by the GROUP BY clause This chapter extends the earlier discussion of joins It illustrates self joins which enable you to join a table to itself and four kinds of outer joins where you apply the keyword OUTER to treat two or more joined tables unequally It also introduces correlated and uncorrelated subqueries and their opera tional keywords shows how to combine queries with the UNION operator and defines the set operations known as union intersection and difference Composing Advanced SELECT Statements 3 3 Using the GROUP BY and HAVING Clauses Examples in this chapter show how to use some or all of the SELECT state
66. WHERE clause or it can refer to a single row the last one fetched through a specified cursor Whenever you delete rows you must consider whether rows in other tables depend on the deleted rows This problem of coordinated deletions is cov ered in Chapter 4 Modifying Data The problem is the same when deletions are made from within a program Modifying Data Through SQL Programs 6 3 Using DELETE Direct Deletions You can embed a DELETE statement in a program The following example uses INFORMIX ESQL C exec sql delete from items where order_num onum You can also prepare and execute a statement of the same form dynamically In either case the statement works directly on the database to affect one or more rows The WHERE clause in the example uses the value of a host variable named onum Following the operation results are posted in the SOLSTATE and in SQLCA as usual The third element of the SOLERRD array contains the count of rows deleted even if an error occurs The value in SQLCODE shows the overall success of the operation If it is not negative no errors occurred and the third element of SQLERRD is the count of all rows that satisfied the WHERE clause and were deleted Errors During Direct Deletions When an error occurs the statement ends prematurely The values in SQLSTATE and in SOLCODE and the second element of SOLERRD explain its cause and the count of rows reveals how many rows were deleted Fo
67. WHERE clause 2 44T on character columns 1 4345 SPL variables 14 18T Subservient table 3 21T Substring 2 27T 14 18T SUM function as aggregate function 2 53T syntax in expression 1 462S use in expression 1 465S Symbol table 10 27T Synonym ANSI compliant naming 1 80S chaining 1 835 chains 12 18T creating with CREATE SYNONYM 1 805 difference from alias 1 80S dropping 1 177S in ANSI compliant database 1 14R synonym behavior in ANSI compliant database 1 14R Synonyms for table names 12 17T Syntax diagram conventions Intro 5S elements of Intro 9S sysdepend system catalog table 1 183S syssyntable 12 18T System catalog accessing 2 8R altering contents 2 9R character column data type when NLS activated 1 19R database entries 1 57S description of 2 3R map of tables 2 33R NCHAR columns in 1 19R privileges in 4 16T 11 9T querying 4 16T sysblobs 2 11R syschecks 2 11R syscolauth 2 12R 1 302S 11 9T syscoldepend 2 13R syscolumns 2 13R sysconstraints 2 16R sysdefaults 2 17R sysdepend 2 18R sysdistrib 2 18R sysindexes 2 20R sysopclstr 2 22R sysprocauth 2 23R sysprocbody 2 24R 14 8T sysprocedures 2 25R sysprocplan 2 26R sysreferences 2 26R syssynonyms 2 27R syssyntable 2 27R systabauth 2 28R 1 2395 1 302S 4 16T 11 9T systables 2 29R systrigbody 2 31R systriggers 2 32R sysusers 2 32R 11 9T sysviews 2 33R updating 2 9R updating statistics 2 9R used by optimizer 13 9T System catalog tables See System catalog Sys
68. What and Why 1015 06 27 93 1 1013 06 22 93 1 each tennis racquet 19 80 06 22 93 1 case tennis ball 36 00 NB 99 Q2 4 raca i 1012 06 18 93 1 case volleyball 840 00 1011 06 18 93 5 each tennis racquet 99 00 1010 06 17 93 1 case tennis ball 36 00 LM ORDERS Searching a file sequentially In contrast when you query a database you use the terms defined by its model To a database you can pose questions such as What orders have been placed for products made by the Shimara Corporation by customers in New Jersey with ship dates in the third quarter Figure 1 3 illustrates this type of query In other words when you interrogate data stored in a file you must state your question in terms of the physical layout of the file When you query a database you can ignore the arcane details of computer storage and state your query in terms that reflect the real world at least to the extent that the data model reflects the real world In this manual Chapters 2 and 3 discuss the language you use for making queries Chapters 8 through 11 discuss designing an accurate robust data model for other users to query Introducing Database Features and SQL 1 7 Databases What and Why state New Jersey manufacturer Shimara order 1019 07 16 93 customer Cathy O Brian customer Bob Shorter order 1023 07 24 93
69. a b FROM customer WHERE customer_num 101 Use the CALL or EXECUTE PROCEDURE statements to assign values returned by a procedure to one or more procedural variables Both statements in the following example return the full address from the procedure read_address into the specified procedural variables EXECUTE PROCEDURE read_address Smith INTO p_fname p_lname p_add p_city p_state p_zip CALL read_address Smith RETURNING p_fname p_lname p_add p_city p_state p_zip Program Flow Control SPL contains several statements that enable you to control the flow of your stored procedure and to make decisions based on data obtained at run time These program flow control statements are described briefly in this section Their syntax and complete descriptions are provided in Chapter 2 of the Informix Guide to SQL Syntax Branching Use an IF statement to form a logic branch in a stored procedure An IF statement first evaluates a condition and if the condition is true the statement block contained in the THEN portion of the statement is executed 14 22 Creating and Using Stored Procedures Figure 14 10 Looping Program Flow Control If the condition is not true execution falls through to the next statement unless the IF statement includes an ELSE clause or ELIF else if clause Figure 14 10 shows an example of an IF statement CREATE PROCEDURE str_compare strl CHAR 20 str2 CHAR 20 RETURNI
70. a given database server such as all procedures run by an SQL API or in a DB Access session The values of the variables are lost when the session ends Global variables require a default value to be assigned at compile time The first definition of a global variable puts the variable into the global environment Subsequent definitions of the same variable in different procedures simply bind the variable to the global environment Defining Variables You define variables using the DEFINE statement If you list a variable in the argument list of a procedure the variable is defined implicitly and you do not need to define it formally with the DEFINE statement You must assign a value which may be null to a variable before you can use it Data Types for Variables You can define a variable as any of the data types available for columns in a table except SERIAL The following example shows several cases of defined procedural variables DEFINE x INT DEFINE name CHAR 15 DEFINE this_day DATETIME YEAR TO DAY If you define a variable for TEXT or BYTE data the variable does not actually contain the data instead it serves as a pointer to the data However you use this procedural variable as you would use any other procedural variable Creating and Using Stored Procedures 14 17 Variables and Expressions When you define a TEXT or BYTE variable you must use the word REFERENCES which emphasizes that these variables
71. a table The information available to the optimizer comes from the system catalog tables See Chapter 2 of the Informix Guide to SQL Reference for information on system catalog tables In all Informix database servers this information includes The number of rows in a table as of the most recent UPDATE STATISTICS command Whether a column is constrained to be unique e The indexes that exist on a table including the columns they encompass whether they are ascending or descending and whether they are clustered e Data distribution information about filtered columns The system catalog tables maintained by INFORMIX OnLine Dynamic Server supply the following additional input The number of disk pages occupied by row data e The depth of the index B tree structure a measure of the amount of work needed to perform an index lookup The number of disk pages occupied by index entries The number of unique entries in an index divided by the number of rows this suggests how many rows might match to a given key e Second largest and second smallest key values in an indexed column Only the second largest and second smallest key values are noted because the extreme values might be special out of range signals The database server assumes that key values are distributed smoothly between the second largest and second smallest Only the initial four bytes of these keys are stored In addition if the index columns have dis
72. and ask yourself the following questions What is being done You may identify excess or redundant steps that can be eliminated Even if every step or action is important it can help you to know them all and their sequence of use e Why is it being done Especially in older applications you may find steps that serve no purpose for example an operation might have been put in long ago for debugging and never removed e For whom is it being done Make sure that all output from the application is wanted and used by someone You may find output that nobody wants any more or the output may be needed infrequently or in a simpler format Where is the slow part Isolate as closely as possible which steps are too slow Your time is limited too spend time where it yields the best results By taking the time to understand the application you can know all its parts how they are used whether they are all essential and which parts are too slow Optimizing Your Queries 13 5 Optimizing Techniques Measuring the Application You cannot make meaningful progress on a performance problem until you have measured it You must find a way to take repeatable quantitative measurements of the slow parts of the application This is crucial for the following reasons e Without numbers you cannot accurately and specifically describe the problem to users or to the organization To convey the problem appropriately you need to determine m
73. arate the columns into volatile ones that are updated constantly and static ones that are rarely updated If so consider splitting the tables so that the volatile columns are isolated in a companion table Depending on the mix of operations and on the priorities of the users you can then put either the static or the volatile subtable on your fastest disk drive Dispersing Bottleneck Tables Small tables are sometimes used for summaries usage records and audits For example your interactive programs can maintain a table with a row for each authorized user Each time the user starts or ends a program it updates that user s row to show time on time off number of transactions or other work monitoring data Small tables that are only read do not cause performance problems but small tables that are the subject of concurrent updates do Any small table that must be updated on every transaction can become a bottleneck in which every on line program queues up and waits To eliminate the problem either use a journal with off peak updates as described earlier or disperse the bottleneck by creating many tables To monitor users create a one row table for each user Tuning Your Data Model 10 35 Summary Summary When tables are moderate in size and only one user at a time accesses the database carefully applied relational theory is sufficient to produce good performance When both the number of tables and the number of users be
74. as described in Chapter 4 Modifying Data with the additional feature that you can use host variables in expressions both in the VALUES and WHERE clauses Moreover a program has the additional ability to insert rows using a cursor Using an Insert Cursor The DECLARE CURSOR statement has many variations Most are used to create cursors for different kinds of scans over data but one variation creates a special kind of cursor called an insert cursor You use an insert cursor with the PUT and FLUSH statements to efficiently insert rows into a table in bulk 6 8 Modifying Data Through SQL Programs Using INSERT Declaring an Insert Cursor Figure 6 3 You create an insert cursor by declaring a cursor to be FOR an INSERT statement instead of a SELECT statement You cannot use such a cursor to fetch rows of data you can use it only to insert them An example of the declaration of an insert cursor is shown in Figure 6 3 iw EFINE the_company LIKE customer company the_fname LIKE customer fname the_lname LIKE customer lname ECLARE new_custs CURSOR FOR INSERT INTO customer company fname lname VALUES the_company the_fname the_lname iw A AGL fragment that declares an insert cursor When you open an insert cursor a buffer is created in memory to hold a block of rows The buffer receives rows of data as the program produces them then they are passed to the database server in a block when the bu
75. before applying massive changes to data during off peak hours Table Locks You can lock entire tables In some cases this is done automatically INFORMIX OnLine Dynamic Server always locks an entire table while it performs any of the following statements ALTER INDEX ALTER TABLE CREATE INDEX DROP INDEX RENAME COLUMN RENAME TABLE The completion of the statement or end of the transaction releases the lock An entire table also can be locked automatically during certain queries You can use the LOCK TABLE statement to lock an entire table explicitly This statement allows you to place either a shared lock or an exclusive lock on an entire table A shared table lock prevents any concurrent updating of that table while your program is reading from it INFORMIX OnLine Dynamic Server achieves the same degree of protection by setting the isolation level as described in the next section this allows greater concurrency However all Informix database servers support the LOCK TABLE statement An exclusive table lock prevents any concurrent use of the table This has a serious effect on performance if many other programs are contending for the use of the table As with an exclusive database lock an exclusive table lock is often used when massive updates are applied during off peak hours For example some applications do not update tables during the hours of peak use Instead they write updates to an update journal During off peak hou
76. box 110 ANZ helmet 244 00 case 4 case 205 ANZ 3 golf balls 312 00 case 24 case 8 ANZ volleyball 840 00 case 24 case 302 HRO ice pack 4 50 each each 309 HRO ear drops 40 00 case 20 case 113 SHM 18 spd assmbld 685 90 each each 5 SMT tennis racquet 25 00 each each 6 SMT tennis ball 36 00 case 24 cans case 1 SMT baseball gloves 450 00 case 10 gloves case Query Result 2 9 Query 2 10 shows the reversed order of the columns in the ORDER BY clause SELECT FROM stock ORDER BY unit_price manu_code Query 2 10 2 16 Composing Simple SELECT Statements Single Table SELECT Statements In Query Result 2 10 the data appears in ascending order of unit_price and where two or more rows have the same unit_price for example 20 00 48 00 312 00 the manu_code is in alphabetical order stock_num manu_code description 302 HRO 302 KAR 5 ANZ 9 ANZ 103 PRC 106 PRC 5 SMT 301 HRO 204 KAR 108 SHM 6 ANZ 305 HRO 303 PRC 311 SHM 110 205 HSK ANZ 205 HRO 205 NKL 1 SMT 4 HRO 102 PRC 111 SHM 112 SHM 7 HRO 203 NKL 113 SHM 1 HSK 8 ANZ 4 HSK Query Result 2 10 ice pack ice pack tennis racquet volleyball net frnt derailleur bicycle stem tennis racquet running shoes putter crankset tennis ball first aid kit socks water gloves helmet 3 golf balls 3 golf balls 3 golf balls baseball gloves football bicycle brakes 10 spd assmbld 12 spd assmbld basketball irons wedge 18 spd
77. child b child c child d child FROM contains a OUTER contains b OUTER contains c outer contains d WHERE a parent top_part_number AND a child b parent AND b child c parent AND c child d parent This SELECT statement returns one row for each line of descent rooted in the part given as top_part_number Null values are returned for levels that do not exist Use indicator variables to detect them You can extend this solu tion to more levels by selecting additional nested outer joins of the contains table You also can revise this solution to return counts of the number of parts at each level Dynamic SQL Although static SQL is extremely useful it requires that you know the exact content of every SQL statement at the time you write the program For exam ple you must state exactly which columns are tested in any WHERE clause and exactly which columns are named in any select list This is no problem when you write a program to perform a well defined task But the database tasks of some programs cannot be perfectly defined in advance In particular a program that must respond to an interactive user might need the ability to compose SQL statements in response to what the user enters 5 28 Programming with SQL Dynamic SQL Dynamic SQL allows a program to form an SQL statement during execution so that the contents of the statement can be determined by user input This is done in the following steps 1 The
78. columns You do this by listing an expression in the select list An expression consists of a column name a constant a quoted string a keyword or any combination of these items connected by operators It also can include host variables program data when the SELECT statement is embedded in a program For more information see the section Expression in Chapter 1 of the Informix Guide to SQL Syntax Arithmetic Expressions An arithmetic expression contains at least one of the arithmetic operators listed in Figure 2 4 and produces a number You cannot use TEXT or BYTE columns in arithmetic expressions Operator Operation addition subtraction i multiplication division Figure 2 4 Arithmetic operators used in arithmetic expressions Operations of this nature enable you to see the results of proposed computations without actually altering the data in the database You can add an INTO TEMP clause to save the altered data in a temporary table for further reference computations or impromptu reports Query 2 37 calculates a 7 percent sales tax on the unit_price column when the unit_price is 400 or more but does not update it in the database SELECT stock_num description unit unit_descr unit_price unit_price 1 07 FROM stock WHERE unit_price gt 400 Query 2 37 2 46 Composing Simple SELECT Statements Single Table SELECT Statements If you are using the DB Access or INFORMIX SQL Interactive
79. create a self join list a table twice in the FROM clause assigning it a different alias each time Use the aliases to refer to the table in the SELECT and WHERE clauses as if it were two separate tables Aliases in SELECT state ments are shown in Chapter 2 Composing Simple SELECT Statements of this manual and discussed in Chapter 1 of the Informix Guide to SQL Syntax Composing Advanced SELECT Statements 3 11 Creating Advanced Joins Just as in joins between tables you can use arithmetic expressions in self joins You can test for null values and you can ORDER BY a specified column in ascending or descending order Query 3 9 finds pairs of orders where the ship_weight differs by a factor of five or more and the ship_date is not null and orders the data by ship_date SELECT x order_num x ship_weight x ship_date y order_num y ship_weight y ship_date FROM orders x orders y WHERE x ship_weight gt 5 y ship_weight AND x ship_date IS NOT NULL AND y ship_date IS NOT NULL ORDER BY x ship_date Query 3 9 order_num ship_weight ship_date order_num ship_weight ship_date 004 95 80 05 30 1993 011 0 40 07 03 1993 004 95 80 05 30 1993 020 4 00 07 16 1993 004 95 80 05 30 1993 022 5 00 07 30 1993 007 125 90 06 05 1993 015 20 60 07 16 1993 007 125 90 06 05 1993 020 4 00 07 16 1993 007 125 90 06 05 1993 022 5 00 07 30 1993 007 125 90 06 05 1993 0 0 40 07 03 1993 007 125 90 06 05 1993 00 20 40 06 01 1993 007 125 90 06 05
80. current row is released and the new row is locked You can be sure by fetching through an update cursor that the fetched row is locked as long as you use it The row cannot become stale You are also assured of fetching only committed data because locks on rows that are updated are held until the end of the transaction Depending on the host operating system and the database server you might experience a performance penalty for using an update cursor this way Locking Updated Rows When a cursor is declared FOR UPDATE locks are handled as follows Before a row is fetched it is locked or if it cannot be locked the program waits or returns an error The next time a fetch is requested the database server notes whether the current row is modified using either the UPDATE or DELETE statement with WHERE CURRENT OF and whether a transaction is in progress If both these things are true the lock on the row is retained Otherwise the lock is released So if you perform updates within a transaction all updated rows remain locked until the transaction ends Rows that are not updated are locked only while they are current Rows updated outside a transaction or in a database that does not use transaction logging are also unlocked as soon as another row is fetched Programming for a Multiuser Environment 7 17 Hold Cursors Hold Cursors Figure 7 1 When transaction logging is used the database server guarantees that anything d
81. cyclic queries The only exception is correlated subqueries In correlated subqueries the subquery or inner SELECT is correlated when the value it produces depends on a value produced by the outer SELECT state ment that contains it If you have implemented cascading deletes you cannot write deletes that use a child table in the correlated subquery You receive an error when you attempt to delete from a correlated subquery Interrupted Modifications 4 22 Modifying Data Even if all the software is error free and all the hardware is utterly reliable the world outside the computer can interfere It is possible for lightning to strike the building interrupting the electrical supply and stopping the com puter in the middle of your UPDATE statement It is more likely however that a disk fills up or a user supplies incorrect data causing your multirow insert to stop early with an error In any case as you are modifying data you must assume that some unforeseen event can interrupt the modification When a modification is interrupted by an external cause you cannot be sure how much of the operation was completed Even in a single row operation you cannot know whether the data reached the disk or the indexes were properly updated Interrupted Modifications If multirow modifications are a problem multistatement ones are worse It does not help that they are usually embedded in programs so that you do not see the individual SQL stateme
82. dat and index idx files in the dbname dbs directory If you specify a dbspace name it will be ignored To use the database and the command files that have been copied to your directory you must have UNIX read and execute permissions for each directory in the pathname of the directory from which you ran the dbaccessdemo6 script 5 To give someone else the permissions to access the command files in your directory use the UNIX chmod command 6 To give someone else the access to the database that you have created grant them the appropriate privileges using the GRANT statement To remove privileges use the REVOKE statement The GRANT and REVOKE statements are described in Chapter 1 of the Informix Guide to SQL Syntax New Features in Informix Version 6 0 Products That Use SOL The Introduction to each Version 6 0 product manual contains a list of new features for that product The Introduction to each manual in the Version 6 0 Informix Guide to SQL series contains a list of new SQL features A comprehensive listing of all the new features for Version 6 0 Informix products is found in the Release Notes file called SERVERS_6 0 Introduction 9 New Features in Informix Version 6 0 Products That Use SQL 10 Introduction This section highlights the major new features implemented in Version 6 0 of Informix products that use SQL e Native Language Support Native Language Support NLS makes Informix Version 6 0 products ad
83. database software provides the means to control database use When you design a database you can perform any of the following functions Keep the database completely private Open its entire contents to all users or to selected users e Restrict the selection of data that some users can view In fact you can reveal entirely different selections of data to different groups of users e Allow specified users to view certain items but not modify them e Allow specified users to add new data but not modify old data e Allow specified users to modify all or specified items of existing data e Ensure that added or modified data conforms to the data model The facilities that make these and other things possible are discussed in Chapter 11 Granting and Limiting Access to Your Database Centralized Management Databases that are used by many people are highly valuable and must be protected as important business assets This creates two significant problems protecting data and maintaining performance The INFORMIX OnLine Dynamic Server database server allows you to centralize these tasks Databases must be guarded against loss or damage The hazards are many failures in software and hardware and the risks of fire flood and other nat ural disasters Losing an important database creates a huge potential for damage The damage could include not only the expense and difficulty of re creating the lost data but also the loss of p
84. digits treated as zeros This lack of exactitude is fine for many uses but you should never use a floating point data type to record money or any other quantity for which it is an error to change the least significant digits to zero Two sizes of floating point data types exist The FLOAT type is a double precision binary floating point number as implemented in the C lan guage on your computer One usually takes up 8 bytes The SMALLFLOAT also known as REAL type is a single precision binary floating point number that usually takes up 4 bytes The main difference between the two data types is their precision A FLOAT column retains about 16 digits of its values a SMALLFLOAT column retains only about 8 digits Floating point numbers have the following advantages e They store very large and very small numbers including fractional ones e They represent numbers compactly in 4 or 8 bytes Implementing Your Data Model 9 9 Defining the Domains e Arithmetic functions such as AVG MIN and sort comparisons are efficient on these data types The main disadvantage of floating point numbers is that digits outside their range of precision are treated as zeros Adjustable Precision Floating Point DECIMAL p The DECIMAL p data type is a floating point type similar to FLOAT and SMALLFLOAT The important difference is that you specify how many signif icant digits it retains The precision you write as p may range from 1 to 32 f
85. disk pages for rows Additional pages for TEXT and BYTE columns are estimated in Estimating Blobpages on page 10 17 An estimate for the customer table is shown in Figure 10 6 Tuning Your Data Model 10 13 Calculating Table Sizes Variable estrows pagesize pageuse rowsize homerow overpage datrows datpages expages Estimate Basis of Estimate 1 500 company business plan 2 048 output of onstat 2 020 pagesize 28 138 sum of 4 column data type size customer_num SERIAL 4 fname CHAR 15 15 Iname CHAR 15 15 company CHAR 20 20 address1 CHAR 20 20 address2 CHAR 20 20 city CHAR 15 15 state CHAR 2 2 zipcode CHAR 5 5 phone CHAR 18 18 134 rowsize lt pageuse 0 rowsize lt pageuse 14 floor pageuse homerow 108 ceiling estrows datrows 0 estrows X overpage Figure 10 6 Estimating the size of the customer table Estimating Variable Length Rows When a table contains one or more VARCHAR columns or NVARCHAR columns when NLS has been enabled its rows have varying lengths This introduces uncertainty You must form an estimate of the typical size of each VARCHAR column based on your understanding of the data When INFORMIX OnLine Dynamic Server allocates space to rows of varying size it considers a page to be full when no room exists for an additional row of the maximum size This can limit the allocation of rows to pages Calculate the following variables MaxroWw typrow homerow
86. do not contain the data they simply reference the data The following example shows the definition of a TEXT and a BYTE variable DEFINE ttt REFERENCES TEXT DEFINE bbb REFERENCES BYTE Using Subscripts with Variables You can use subscripts with variables having CHAR VARCHAR NCHAR NVARCHAR BYTE or TEXT data types just as you can with SQL column names The subscripts indicate the starting and ending character positions of the variable Subscripts must always be constants You cannot use variables as subscripts The following example illustrates the usage DEFINE name CHAR 15 LET name 4 7 Ream SELECT fname 1 3 INTO name 1 3 FROM customer WHERE lname Ream The portion of the variable contents that is delimited by the two subscripts is referred to as a substring Scope of Variables A variable is valid within the statement block in which it is defined It is valid within statement blocks nested within that statement block as well unless it is masked by a redefinition of a variable with the same name In the beginning of the procedure in Figure 14 9 the integer variables x y and z are defined and initialized The BEGIN and END statements mark a nested statement block in which the integer variables x and q are defined as 14 18 Creating and Using Stored Procedures Variables and Expressions well as the CHAR variable z Within the nested block the redefined variable
87. done right you must examine every aspect of the data not once but several times If you are interested in learning more about database design you can attend the Informix course Relational Database Design This thorough course presents how to create an entity relationship data model If you are interested in pursuing more about database design on your own the following excellent books are recommended Database Modeling and Design The Entity Relationship Approach by Toby J Teorey Morgan Kauffman Publishers Inc 1990 e Handbook of Relational Database Design by Candace C Fleming and Barbara von Halle Addison Wesley Publishing Company 1989 Building Your Data Model 8 33 Summary 8 34 Building Your Data Model Implementing Your Data Model Chapter Overview 3 Defining the Domains 3 Data Types 4 Choosing a Data Type 4 Numeric Types 7 Chronological Types 12 Character Types 15 Changing the Data Type 19 Default Values 19 Check Constraints 20 Creating the Database 20 Using CREATE DATABASE 21 Using CREATE DATABASE with INFORMIX OnLine Dynamic Server 21 Using CREATE DATABASE with Other Informix Database Servers 23 Using CREATE TABLE 24 Using Command Scripts 26 Capturing the Schema 26 Executing the File 26 An Example 26 Populating the Tables 27 Summary 29 9 2 Implementing Your Data Model Chapter Overview Once a data model is prepared it must be implemented as a database and tables This chapter co
88. entity type These types of relationships do not occur often Examples of recursive relationships are bill of materials parts are composed of subparts and organizational structures employee manages employees See Chapter 5 Programming with SQL for an extended example of a recursive relationship You may choose not to resolve recursive relationships 8 28 Building Your Data Model Normalizing Your Data Model A redundant relationship is when two or more relationships are used to represent the same concept Redundant relationships add complexity to the data model and may lead a developer to incorrectly place attributes in the model Redundant relationships may appear as duplicated entries in your entity relationship diagram For example you may have two entities that contain the same attributes To resolve a redundant relationship review your data model Do you have more than one entity that contains the same attributes You may need to add an entity to the model to resolve the redundancy Chapter 10 Tuning Your Data Model discusses additional topics related to redundancy in a data model Normalizing Your Data Model The telephone directory example shown in this chapter appears to be a good model It could be implemented at this point into a database but it might present problems later on with application development and data manipula tion operations Normalization is a formal approach to applying a set of rules used in a
89. every column and row in the manufact table Query Result 2 5 shows the results as they would appear on a DB Access or INFORMIX SQL Interactive Schema Editor ISED screen manu_code manu_name lead_time SMT Smith 3 ANZ Anza 5 NRG Norge 7 HSK Husky 5 HRO Hero 4 SHM Shimara 30 KAR Karsten 21 NKL Nikolus 8 PRC ProCycle 9 Query Result 2 5 2 12 Composing Simple SELECT Statements Single Table SELECT Statements Reordering the Columns Query 2 6 shows how you can change the order in which the columns are listed by changing their order in your select list SELECT manu_name manu_code lead_time FROM manufact Query 2 6 Query Result 2 6 includes the same columns as the previous one but because the columns are specified in a different order the display is also different manu_name manu_code lead_time Smith SMT 3 Anza ANZ 5 Norge NRG 7 Husky HSK 5 Hero HRO 4 Shimara SHM 30 Karsten KAR 27T Nikolus NKL 8 Procycle PRC 9 Query Result 2 6 Sorting the Rows You can direct the system to sort the data in a specific order by adding an ORDER BY clause to your SELECT statement The columns you want to use in the ORDER BY clause must be included in the select list either explicitly or implicitly An explicit select list shown in Query 2 7a includes all the column names that you want to retrieve SELECT manu_code manu_name lead_time FROM manufact ORDER BY lead_time Query 2 7a Composing Simple SELEC
90. f 1oor x means the largest integer smaller than x and ceiling x means the smallest integer larger than x 10 12 Tuning Your Data Model Calculating Table Sizes Estimating Fixed Length Rows When a table contains no VARCHAR columns its rows all have the same size Calculate the following additional variables Let the values be as shown in the following list rowsize the sum of the sizes of all columns in the table plus 4 bytes Sizes of different data types are discussed in Chapter 9 Implementing Your Data Model Treat TEXT and BYTE columns as having size 56 homerow if rowsize lt pageuse then rowsize lse 4 remainder rowsize pageuse If a row is larger than a page as many full pages as possible are removed from the end of the row and stored in separate expan sion pages Let homerow be the size of the leading part which is kept on the home page The value homerow is simply rowsize if a row fits a page overpage if rowsize lt pageuse then 0 else floor rowsize pageuse Let overpage be the number of expansion pages needed for each row it is zero when a row fits on a page datrows min 255 floor pageuse homerow Let datrows be the number of rows or leading parts of rows that fits on one page An upper limit exists of 255 rows per page even when rows are very short datpages ceiling estrows datrows expages estrows X overpage The table requires approximately datpages expages
91. faster than a human can But some queries must be performed in a limited amount of time or must use only a limited amount of machine power This chapter reviews techniques for making queries more efficient It assumes that you work with an existing database and cannot change its arrangement of tables Techniques of designing a new database for reliability and performance are discussed in Chapters 8 through 11 This chapter covers the following topics e A discussion of techniques for optimizing software emphasizing all the things to look at before you change any SQL statement e A discussion of the optimizer the part of the database server that decides how to perform a query When you know what the optimizer looks for when it forms a query plan you can help it form more efficient ones e A discussion of the operations that take time during a query so you can better choose between fast and slow operations e An assortment of techniques to help the optimizer choose the fastest way to accomplish a query This chapter concentrates on SQL performance but performance problems can arise from other parts of the programs in which SQL statements are embedded Two books that address general issues of performance are The Elements of Programming Style by Kernighan and Ritchie McGraw Hill 1978 and Writing Efficient Programs by Jon Louis Bentley Prentice Hall 1982 Much of Bentley s advice can be applied to SQL statements and database de
92. for performance 10 30T produced by view 11 20T DESC keyword 1 338S syntax in CREATE INDEX 1 63S in SELECT 1 337S use in CREATE INDEX 1 665 in SELECT 1 338S Descending order in SELECT 2 14T DESCRIBE statement and COLLCHAR environment variable 4 46R and the USING SQL DESCRIPTOR clause 1 164S describing statement type 1 163S 5 33T INTO sqlda pointer clause 1 165S relation to GET DESCRIPTOR 1 213S syntax 1 162S using with concatenation operator 1 432S values returned by SELECT 1 163S Descriptor 1 164S Determining ANSI compliance 1 10R Device optical 12 6T storage 12 6T Directory extension dbs 1 585 1 141S Dirty Read isolation level 1 3675 7 10T DIRTY READ keywords syntax in SET ISOLATION 1 366S DISCONNECT statement 1 169S ALL keyword 1 169S CURRENT keyword 1 1685 with concatenation operator 1 432S Disk access chunk 10 4T Index 15 16 Index cost to read a row 13 16T dbspace 10 4T latency of 13 17T nonsequential 13 18T nonsequential avoided by sorting 13 37T performance 13 17T to 13 19T 13 34T reducing contention 10 7T seek time 13 17T sequential 13 17T 13 34T sequential forced by query 13 32T 13 33T 13 35T using rowid 13 18T Disk buffer See Page buffer Disk contention effect of 13 17T multiple arms to reduce 10 7T Disk extent 10 8T Disk mirroring 10 5T Disk page buffer for 13 16T 13 18T size of 10 4T 13 14T Display label in ORDER BY clause 2 52T syntax in SELECT 1 3125 with SELEC
93. group Query 3 2 returns one row for each group It uses labels to give names to the results of the COUNT and SUM expressions as shown in Query Result 3 2 order_num number price 1001 1 250 00 1002 2 1200 00 1003 3 959 00 1004 4 1416 00 1005 4 562 00 1006 5 448 00 1007 5 1696 00 1008 2 940 00 1015 1 450 00 1016 4 654 00 1017 3 584 00 1018 5 1131 00 1019 1 1499 97 1020 2 438 00 1021 4 1614 00 1022 3 232 00 1023 6 824 00 Query Result 3 2 Query Result 3 2 collects the rows of the items table into groups that have identical order numbers and computes the COUNT of rows in each group and the sum of the prices 3 6 Composing Advanced SELECT Statements Using the GROUP BY and HAVING Clauses Note that you cannot include a column having a TEXT or BYTE data type ina GROUP BY clause To group you must be able to sort and no natural sort order exists for TEXT or BYTE data Unlike the ORDER BY clause the GROUP BY clause does not order data Include an ORDER BY clause after your GROUP BY clause if you want to sort data in a particular order or to sort on an aggregate in the select list Query 3 3 is the same as Query 3 2 but includes an ORDER BY clause to sort the retrieved rows in ascending order of price as shown in Query Result 3 3 SELECT order_num COUNT FROM items GROUP BY order_num ORDER BY price Query 3 3 order_num number 1010 1011 1013 1022 1001 1020 1006 1015 1009 PRPON
94. how to set in Korn shell 4 5R INFORMIX environment variables listing 4 8R NFORMIXC 4 31R NFORMIXCOB 4 32R NFORMIXCOBDIR 4 32R NFORMIXCOBSTORE 4 33R NFORMIXCONRETRY 4 34R NFORMIXCONTIME 4 34R NFORMIXDIR 4 36R 12 14T NFORMIXSERVER 4 36R 12 14T NFORMIXSHMBASE 4 37R NFORMIXSTACKSIZE 4 38R INFORMIXTERM 4 38R LANG 4 49R LANG and crtcmap utility 5 5R LC_COLLATE 4 50R LC_CTYPE 4 51R LC_MONETARY 4 52R LC_NUMERIC 4 53R LC_TIME 4 53R listed 4 8R listed by topic 4 9R listed for NLS 4 9R listed for UNIX 4 9R NLS environment variables listing 4 9R ONCOMFIG 4 39R overriding a setting 4 4R 4 30R PATH 4 54R 12 14T PSORT_DBTEMP 4 40R PSORT_NPROCS 4 41R rules of precedence 4 7R setting at the command line 4 4R setting in a shell file 4 4R SQLEXEC 4 41R SQLRM 4 41R 4 42R SQLRMDIR 4 43R TERM 4 55R TERMCAP 4 56R 12 14T TERMINFO 4 56R UNIX environment variables listing 4 9R where to set 4 4R Te cee cee aas cee cee A ee ee ee B an Index 17 18 Index Equals relational operator 2 30T 2 71T Equi join 2 71T ERROR 1 400S Error checking continuing after error in stored procedure 2 345 error status with ON EXCEPTION 2 328 exception handling 14 27T in stored procedures 14 27T simulating errors 14 31T with SYSTEM 2 40S ERROR keyword in the WHENEVER statement 1 398S Error messages for NLS 1 21R for trigger failure 15 14T generating in a trigger 15 14T retrieving t
95. in the WHERE clause it eliminates duplicate manufacturer codes in rows retrieved SELECT sl manu_code s2 manu_code s3 manu_code sl stock_num sl description FROM stock sl stock s2 stock s3 WHERE sl stock_num s2 stock_num AND s2 stock_num s3 stock_num AND sl manu_code s2 manu_code AND s2 manu_code s3 manu_code ORDER BY stock_num lt lt Query 3 11 manu_code manu_code manu_code stock_num description HRO HSK SMT 1 baseball gloves ANZ RG SMT 5 tennis racquet ANZ HRO HSK 110 helmet ANZ HRO PRC LO helmet ANZ HRO SH LO helmet ANZ HSK PRC LO helmet ANZ HSK SH LO helmet ANZ PRC SH LO helmet HRO HSK PRC LO helmet HRO HSK SH LO helmet HRO PRC SH 110 helmet HSK PRC SH 110 helmet ANZ KAR KL 201 golf shoes ANZ HRO KL 205 3 golf balls ANZ HRO KAR 301 running shoes HRO PRC SHM 301 running shoes KAR NKL PRC 301 running shoes KAR NKL SHM 301 running shoes KAR PRC SHM 301 running shoes NKL PRC SHM 301 running shoes Query Result 3 11 3 14 Composing Advanced SELECT Statements Creating Advanced Joins Say you want to select rows from a payroll table to determine which employees earn more than their manager You can construct the self join shown in Query 3 12a SELECT emp employee_num emp gross_pay emp level emp dept_num mgr employee_num mgr gross_pay mgr dept_num mgr level FROM payroll emp payroll mgr WHERE emp gross_pay gt mgr gross_pay AND emp le
96. in any par ticular order The sizes of these tables indicate that the odds of a successful nonsequential access from a buffered page are very poor 13 38 Optimizing Your Queries Figure 13 7 Making Queries Faster The best query plan for this query not necessarily the one the optimizer chooses is to read the part table sequentially first then use the value of part_num to access the matching rows of parven about 1 5 of them per part and then use the value of parven vendor_num to access vendor through its index Tables Row Size RowCount Rows Page Data Pages part 150 10 000 25 400 vendor 150 1 000 25 40 parven 13 15 000 300 50 Indexes Key Size Keys Page Leaf Pages part_num 4 500 20 vendor_num 4 500 2 parven composite 8 250 60 Documenting the sizes of tables and indexes in pages The resulting number of disk accesses is estimated as shown in the following list e 400 pages read sequentially from part 10 000 nonsequential accesses to the parven table 2 pages each one index leaf page one data page or 20 000 disk pages e 15 000 nonsequential accesses to the vendor table or 30 000 disk pages Even a simple join on well indexed tables can require 50 400 disk reads How ever this can be improved by breaking the query into three steps using tem porary tables as shown in Figure 13 8 The following solution comes from W H Inmon it is adapted from an example in his book Optimizing Performance in DB2 Software
97. is INFORMIX 4GL a nonprocedural language designed expressly for writing database applications However you can also communicate with an Informix database server from programs that contain embedded SQL written in C COBOL Ada and FORTRAN You also can write programs called stored procedures to work with database data and objects The stored procedures that you write are stored directly in a database within tables You can then execute a stored procedure from DB Access or an SQL API Chapter 5 Programming with SQL and Chapter 6 Modifying Data Through SQL Programs present an overview of how SQL is used in rograms Applications and Database Servers Summary Every program that uses data from a database operates the same way Regardless of whether it is a packaged program such as INFORMIX SQL a report program compiled by ACE or a program that you wrote using INFORMIX 4GL or an SQL API you find the same two layers in every case 1 An application that interacts with the user prepares and formats data and sets up SQL statements 2 A database server that manages the database and interprets the SQL All the applications converge on the database server and only the database server manipulates the database files on disk A database contains a collection of related information but differs in a fundamental way from other methods of storing data The database contains not only the data but also a data model that defines e
98. man ager Transaction managers are third party products such as TUXEDO In this context a resource manager corresponds to a database server Figure 12 5 illustrates a configuration that uses transaction processing Understanding Informix Networking 12 11 Connecting to Data on a UNIX Network interface interface transaction manager client portion of each application server portion of each application lt INFORMIX OnLine XA vendor a s DBMS XA vendor b s DBMS XA resource managers databases Figure 12 5 A configuration using a transaction manager Connecting to Data on a UNIX Network When the application and data are moved to separate computers two questions immediately arise What connections can you implement How do you instruct your applications to find the data that is now somewhere else In fact connecting a client application to a database server that is on a networked computer is no different from connecting to a local database server To connect a client application with a database you must consider the following parts of your configuration Environment variables Connection information Connection statements 12 12 Understanding Informix Networking Connecting to Data on a UNIX Network This section summarizes how connections are made for Version 6 0 clients and
99. matrix that reflects the entities for a personal telephone directory You can ignore the lower triangle of the matrix as indicated by the shaded area You must consider the diagonal cells that is you must ask the question What is the relationship between an A and another A In this model the answer is always none No relationship exists between a name and a name or an address and another address at least none worth recording in this model When a relationship exists between an A and another A you have found a recursive relationship See Resolving Other Special Relationships on page 8 28 For all cells for which the answer is clearly none write none in the matrix Now the matrix looks like Figure 8 4 8 10 Building Your Data Model Figure 8 4 Identifying and Defining Your Principal Data Objects name address number number number voice fax modem name none address none number none voice number none fax number none modem A matrix with initial relationships included No entities relate to themselves Although in this model no entities relate to themselves in other models this is not always true A typical example is an employee who is the manager of another employee Another example occurs in manufacturing when a part entity is a component of another part In the remaining cells you write the connectivity relationship that exists between the entity
100. more than 234 extents as calculated in Figure 10 3 To help ensure that the limit is not exceeded OnLine checks the number of extents each time it creates a new one If the extent being created is the 16th or a multiple of 16 the next extent size for the table is automatically doubled Variable Value Basis pagesize 2 048 output of onstat colspace 40 ten columns ixspace 36 three indexes ixparts 12 one column in each index extspace 1 876 2 048 40 36 12 84 limit 234 extspace 8 Figure 10 3 Values used to determine upper limit on extents Reorganizing dbspaces and Tables Query performance can suffer after many extents are added to a table This can only be the case when two or more large growing tables share a dbspace When tables grow at the same time their new extents and index pages are interleaved creating large gaps between the extents of any one table This situation is shown in Figure 10 4 10 10 Tuning Your Data Model Figure 10 4 Figure 10 5 INFORMIX OnLine Dynamic Server Disk Storage HE table 1 2 nn table 3 A dbspace with interleaved tables Figure 10 4 also shows gaps of unused space perhaps created by tables that existed when extents were allocated but that have since been dropped Disorganization such as that depicted in Figure 10 4 hurts performance in two ways During sequential access to any table several long seeks must be made For nonsequential access to any
101. multiple access arms per table 10 7T network access 13 20T nonsequential access 13 18T optimizing 13 3T to 13 42T references to other books 13 3T reorganizing a dbspace 10 10T row access 13 16T seek time 13 17T sequential access 13 17T 13 34T sorting replaces nonsequential access 13 37T splitting tall tables 10 29T splitting wide tables 10 28T time costs of query 13 14T use of derived data 10 30T use of redundant data 10 31T using CHAR instead of NCHAR 1 19R Performance analysis 80 20 rule 13 7T measurement 13 6T methods 13 27T to 13 41T nonsequential access 13 37T to 13 41T optimizing techniques 13 4T setting up test environment 13 28T timing from 4GL program 13 6T from command script 13 6T from watch 13 6T using query plan 13 29T verifying problem 13 4T Permission with SYSTEM 2 40S Phantom row 1 367S PIPE keyword in the OUTPUT statement 1 2725 Pipe symbol See concatenation operator Pipes unnamed 12 7T Plus sign arithmetic operator 1 4315 Populating tables 9 27T POW function syntax in expression 1 444S use in expression 1 4465 Precedence rules for environment variables 4 7R PRECISION field setting with SET DESCRIPTOR 1 3585 with GET DESCRIPTOR 1 2145 PREPARE statement description of 5 29T error return in SQLERRD 5 12T executing 1 184S increasing performance efficiency 1 283S missing WHERE signalled 5 10T multiple SQL statements 5 30T multi statement text 1 2775S 1 2815S parameterizing a statem
102. o res_dtime res_descr S E b Query Result 2 73 2 74 Composing Simple SELECT Statements ANZ tennis balls within the case were empty 993 06 12 08 25 Authorized credit for two cans to customer ssued apology Called ANZ buyer to report he ga problem 008 6 07 1993 7 06 1993 10 993 07 07 10 24 iche rder placed one month ago not received 993 07 07 10 30 hecked with shipping Ed Smith Order out esterday was waiting for goods from ANZ ext time will call with delay if necessary 6 7 023 7 24 1993 7 30 1993 27 993 07 31 14 30 ary eceived Hero watches instead f ANZ watches item 304 ent memo to shipping to send ANZ item 304 o customer and pickup HRO watches Should e done tomorrow 8 1 Multiple Table SELECT Statements Natural Join A natural join is structured so that the join column does not display data redundantly as shown in Query 2 74 SELECT manu_name lead_time stock FROM manufact stock WHERE manufact manu_code stock manu_code Query 2 74 Composing Simple SELECT Statements 2 75 Multiple Table SELECT Statements Like the example for equi join Query 2 74 joins the manufact and stock tables on the manu_code column Because the select list is more closely defined the manu_code is listed only once for each row retrieved as shown in Query Result 2 74 manu_name lead_time stock_num manu_code description unit_price unit unit_descr manu_nam
103. o order_num SUM i total_price FROM orders o items i WHERE o order_date gt 01 01 92 AND o customer_num 110 AND o order_num i order_num GROUP BY o order_num Query 3 5 Query 3 5 joins the orders and items tables assigns table aliases to them and returns the rows shown in Query Result 3 5 order_num sum 1008 940 00 1015 450 00 Query Result 3 5 3 8 Composing Advanced SELECT Statements Using the GROUP BY and HAVING Clauses Using the HAVING Clause The HAVING clause usually complements a GROUP BY clause by applying one or more qualifying conditions to groups after they are formed which is similar to the way the WHERE clause qualifies individual rows One advantage to using a HAVING clause is that you can include aggregates in the search condition whereas you cannot include aggregates in the search condition of a WHERE clause Each HAVING condition compares one column or aggregate expression of the group with another aggregate expression of the group or with a constant You can use HAVING to place conditions on both column values and aggregate values in the group list Query 3 6 returns the average total price per item on all orders that have more than two items The HAVING clause tests each group as it is formed and selects those composed of two or more rows SELECT order_num COUNT number AVG total_price average FROM items GROUP BY order_num HAVING COUNT gt 2 Query 3 6 order_n
104. of aggregate functions in subqueries Demonstrated the use of the keywords ALL ANY EXISTS IN and SOME in creating subqueries and the effect of adding the keyword NOT ora relational operator Discussed the set operations union intersection and difference Showed how to use the UNION and UNION ALL keywords to create compound queries consisting of two or more SELECT statements Composing Advanced SELECT Statements 3 55 Summary 3 56 Composing Advanced SELECT Statements Modifying Data Chapter Overview 3 Statements That Modify Data 3 Deleting Rows 4 Deleting All Rows ofa Table 4 Deleting a Known Number of Rows 4 Deleting an Unknown Number of Rows 5 Complicated Delete Conditions 6 Inserting Rows 6 Single Rows 7 Multiple Rows and Expressions 9 Restrictions on the Insert Selection 10 Updating Rows 11 Selecting Rows to Update 12 Updating with Uniform Values 13 Impossible Updates 13 Updating with Selected Values 14 Database Privileges 15 Displaying Table Privileges 16 Data Integrity 17 Entity Integrity 18 Semantic Integrity 18 Referential Integrity 19 Using the ON DELETE CASCADE Option 21 Interrupted Modifications 22 The Transaction 23 Transaction Logging 24 Logging and Cascading Deletes 24 Specifying Transactions 24 Archives and Logs 25 Archiving with INFORMIX SE 26 Archiving with INFORMIX OnLine Dynamic Server 26 Concurrency and Locks 27 Data Replication 28 INFORMIX OnLine Dynamic Server Data Repli
105. of commands The use of these prod ucts is covered in the DB Access User Manual or the INFORMIX SQL User Guide You can start DB Access or INFORMIX SQL and have them read and execute a file of commands prepared by you or by dbschema An Example Most Informix database server products come with a demonstration database called stores6 the one used for most of the examples in this book The stores6 database is delivered as an operating system command script that calls Informix products to build the database You can copy this command script and use it as the basis for automating your own data model 9 26 Implementing Your Data Model Creating the Database Populating the Tables For your initial tests it is easiest to populate the tables interactively by typing INSERT statements in DB Access or INFORMIX SQL As shown in the follow ing example to insert a row into the manufact table of the stores6 database in DB Access you enter the following command INSERT INTO manufact VALUES MKL Martin 15 Or if you are preparing an application program in INFORMIX 4GL or another language you can use the program to enter rows Often the initial rows of a large table can be derived from data held in tables in another database or in operating system files You can move the data into your new database in a bulk operation If the data is in another Informix database you can retrieve it in several ways If you are using INFORMIX
106. of the following items e Data type INTEGER CHAR DATE and so on Format for example yy mm dd Range for example 1 000 5 400 Meaning for example personnel number e Allowable values for example only grades S or U e Uniqueness e Null support Default value Referential constraints You define the domain characteristics when you create your tables Defining domains and creating your tables and database are discussed in Chapter 9 Implementing Your Data Model Determining Keys for Tables The columns of a table are either key columns or descriptor columns A key column is one that uniquely identifies a particular row in the table For exam ple a social security number is unique for each employee A descriptor col umn specifies the nonunique characteristics of a particular row in the table For example two employees may have the same first name Sue The first name Sue is a nonunique characteristic of an employee The main types of keys in a table are primary keys and foreign keys You designate primary and foreign keys when you create your tables Primary and foreign keys are used to relate tables together physically Your next task is to specify a primary key for each table That is you must identify some quantifiable characteristic of the table that distinguishes each row from every other Primary Keys The primary key of a table is the column whose values are different in every row Becau
107. on an indexed column the database server chooses the selected rows through the index and processes only those rows When no filter exists the database server must read all the rows anyway It is usually faster to simply read the rows rather than reading the pages of an index and then reading the rows However if the rows are required in sorted order there may be a net savings in reading the index and through it reading the rows in sorted order The optimizer might choose a third option creating a temporary index in two cases When neither table in a join has an index on the joining column and the tables are large enough the optimizer may decide that it is quicker to build an index to one table than to read through that table sequentially for each row of the other table You can also use a temporary index to generate rows in sorted or grouped sequence The alternative is to write the output rows to a temporary table and sort that The optimizer has a fourth option performing a sort merge join which does not require a temporary index This occurs only when at least one filter of the join is an equality operator and it has been determined that a temporary index would be more costly Selecting the Query Plan With all this information available the optimizer generates all possible query plans for joining tables in pairs Then if more than two tables are joined the optimizer uses the best two table plans to form all plans for join
108. only an approximation however when the database is available to multiple users concurrently Between the time you execute the SELECT statement and the subsequent DELETE statement other users could have modified the table and changed the result In this example another user might perform the following actions e Insert a new row for another customer named Druid Cyclery Delete one or more of the Druid Cyclery rows before you do so e Update a Druid Cyclery row to have a new company name or update some other customer to have the name Druid Cyclery Although it is not likely that other users would do these things in that brief interval the possibility does exist This same problem affects the UPDATE statement Ways of addressing this problem are discussed under Concur rency and Locks on page 4 27 and in greater detail in Chapter 7 Program ming for a Multiuser Environment Another problem you may encounter is a hardware or software failure before the statement finishes In this case the database may have deleted no rows some rows or all specified rows The state of the database is unknown which is undesirable You can prevent this situation by using transaction logging as discussed in Interrupted Modifications on page 4 22 Modifying Data 4 5 Statements That Modify Data Complicated Delete Conditions The WHERE clause in a DELETE statement can be almost as complicated as the one in a SELECT statement It ca
109. p_add p_city p_state p_zip FROM customer WHERE lname lastname RETURN p_fname p_lname p_add p_city p_state p_zip WITH RESUME LET lcount lcount 1 END FOREACH FOR i IN 1 TO 5 BEGIN RETURN a b c d e WITH RESUME END END FOR END PROCEDURE Figure 14 13 Procedure that returns values from a FOREACH loop and a FOR loop When you execute this procedure it returns the name and address for each person with the specified last name It also returns a sequence of letters The calling procedure or program must be expecting multiple returned values and it must use a cursor or a FOREACH statement to handle the multiple returned values Exception Handling You can trap any exception or error returned by the database server to your procedure or raised by your procedure with the ON EXCEPTION statement The RAISE EXCEPTION statement enables you to generate an exception within your procedure Creating and Using Stored Procedures 14 27 Exception Handling Trapping an Error and Recovering Figure 14 14 The ON EXCEPTION statement provides a mechanism to trap any error To trap an error enclose a group of statements in a statement block and precede the statement block with an ON EXCEPTION statement If an error occurs in the block that follows the ON EXCEPTION statement you can take recovery action Figure 14 14 shows an example of an ON EXCEPTION statement within a BEGI
110. privileges are discussed in Chapter 11 Granting and Limiting Access to Your Database of this manual and in the GRANT and REVOKE statements in Chapter 1 of the Informix Guide to SQL Syntax Relational Operations A relational operation involves manipulating one or more tables or relations to result in another table The three kinds of relational operation are selection projection and join This chapter includes examples of selection projection and simple joining Selection and Projection In relational terminology selection is defined as taking the horizontal subset of rows of a single table that satisfies a particular condition This kind of SELECT statement returns some of the rows and all of the columns in a table Selection is implemented through the WHERE clause of a SELECT statement as shown in Query 2 1 SELECT FROM customer WHERE state NJ Query 2 1 Composing Simple SELECT Statements 2 5 Introducing the SELECT Statement Query Result 2 1 contains the same number of columns as the customer table but only a subset of its rows Because the data in the selected columns does not fit on one line of the DB Access or INFORMIX SQL Interactive Schema Editor ISED screen the data is displayed vertically instead of horizontally customer_num fname lname company addressl address2 city state zipcode phone customer_num fname lname company address1 address2 city state zipcode ph
111. pro duced by the outer SELECT statement that contains it Any other kind of subquery is considered uncorrelated The important feature of a correlated subquery is that because it depends on a value from the outer SELECT it must be executed repeatedly once for every value produced by the outer SELECT An uncorrelated subquery is executed only once You can construct a SELECT statement with a subquery to replace two separate SELECT statements Subqueries in SELECT statements allow you to perform the following actions Compare an expression to the result of another SELECT statement Determine whether an expression is included in the results of another SELECT statement Determine whether any rows are selected by another SELECT statement An optional WHERE clause in a subquery often is used to narrow the search condition A subquery selects and returns values to the first or outer SELECT statement A subquery can return no value a single value or a set of values e Ifitreturns no value the query does not return any rows Such a subquery is equivalent to a null value e If it returns one value the subquery returns either one aggregate expression or else selects exactly one row and one column Such a subquery is equivalent to a single number or character value e Ifit returns a list or set of values the subquery returns either one row or one column Composing Advanced SELECT Statements Subqueries in SELECT Statem
112. program might return a mixture of original rows and updated rows 4 Same as number 3 except that after updating the table the other program issues a ROLLBACK WORK statement Your program can show you a mixture of original rows and updated rows that no longer exist in the database The first two possibilities are harmless In number 1 the update is complete before your query begins It makes no difference whether it finished a microsecond or a week ago In number 2 your query is in effect complete before the update begins The other program might have been working just one row behind yours or it might not start until tomorrow night it does not matter The second pair of chances however can be very important to the design of some applications In number 3 the query returns a mix of updated and orig inal data That can be a negative thing in some applications In others for instance one that is taking an average of all prices it might not matter at all In number 4 it can be disastrous if a program returns some rows of data that because their transaction was cancelled can no longer be found in the table Another concern arises when your program uses a cursor to update or delete the last fetched row Erroneous results occur with the following sequence of events e Your program fetches the row e Another program updates or deletes the row e Your program updates or deletes WHERE CURRENT OF names You control concurrent
113. queries of this form by converting them into UNION queries Write a separate SELECT statement for each set of rows and connect them with the UNION keyword The following example shows a rewritten version of the preceding example SELECT FROM orders WHERE customer_num 104 AND order_num gt 1001 UNION SELECT FROM orders WHERE order_num 1008 The optimizer uses an index path for each query You can also rewrite the WHERE clause as shown in the following example WHERE customer_num 104 OR order_num 1008 AND order_num gt 1001 OR order_num 1008 Optimizing Your Queries 13 35 Making Queries Faster Reviewing the Optimization Level You normally obtain optimum overall performance with the default optimization level HIGH The time it takes to optimize the statement is usually unimportant However if experimentation with your application reveals that your query is still taking too long you may want to set your opti mization level to LOW and then check the SET EXPLAIN output to see if the optimizer chose the same query plan as before You can specify a HIGH or LOW level of database server optimization with the SET OPTIMIZATION statement This statement is described in detail in Chapter 1 of the Informix Guide to SQL Syntax Using a Temporary Table to Speed Queries Building a temporary ordered subset of a table can speed up a query It can help to avoid multiple sort operation
114. record order used in Figure 6 2 on page 6 7 In this example the duplicate rows are ordered by their dates the oldest one remains but you can use any other order based on the data Modifying Data Through SQL Programs 6 13 Using UPDATE The second cursor is an insert cursor It is written to take advantage of the asterisk notation of INFORMIX 4GL you can supply values for all columns simply by naming a record with an asterisk to indicate all fields The remainder of the code examines the rows returned through dup_row It inserts the first one from each group of duplicates into the new table and disregards the rest This example uses the simplest kind of error handling Unless told otherwise an INFORMIX 4GL program automatically terminates when an error code is set in SQLCODE In this event the active transaction rolls back This program relies on that behavior it assumes that if it reaches the end no errors exist and the transaction can be committed This kind of error handling is acceptable when errors are unlikely and the program is used by people who do not need to know why the program terminates Using UPDATE You can embed the UPDATE statement in a program in any of the forms described in Chapter 4 Modifying Data with the additional feature that you can name host variables in expressions both in the SET and WHERE clauses Moreover a program can update the row addressed by a cursor How Many Rows Were Affected S
115. row has only a single column and its value is deposited in the host variable named avg_price Subsequent lines of the program can use that variable You can use statements of this kind to retrieve single rows of data into host variables The single row can have as many columns as desired In the follow ing INFORMIX 4GL example host variables are used in two ways as receivers of data and in the WHERE clause DEFINE cfname clname DEFINE cnumbr INTEGER LET cnumbr 104 SELECT fname lname INTO cfname FROM customer WHERE customer_num ccompany CHAR 20 company clname ccompany cnumbr Because the customer_num column has a unique index implemented through a constraint this query returns only one row If a query produces more than one row of data the database server cannot return any data It returns an error code instead You should list as many host variables in the INTO clause as there are items in the select list If by accident these lists are of different lengths the data base server returns as many values as it can and sets the warning flag in the fourth field of SQLAWARN Data Type Conversion The following example retrieves the average of a DECIMAL column which is itself a DECIMAL value However the host variable into which it is placed is not required to have that data type exec sql select avg into from items total_price avg_price 5 14 Programming with SQL Retrievin
116. safety recall of their tennis balls As a result any unshipped orders that include stock number 6 from manufacturer ANZ must be put on back order as shown in the following example UPDATE orders SET backlog y WHERE ship_date IS NULL AND order_num IN SELECT DISTINCT items order_num FROM items WHERE items stock_num 6 AND items manu_code ANZ This subquery returns a column of order numbers zero or more The UPDATE operation then tests each row of orders against the list and performs the update if that row matches 4 12 Modifying Data Statements That Modify Data Updating with Uniform Values Each assignment after the keyword SET specifies a new value for a column That value is applied uniformly to every row that you update In the exam ples in the previous section the new values were constants but you can assign any expression including one based on the column value itself Sup pose the manufacturer code HRO has raised all prices by 5 percent and you must update the stock table to reflect this You would use a statement such as the one shown in the following example UPDATE stock SET unit_price unit_price 1 05 WHERE manu_code HRO You can also use a subquery as part of the assigned value When a subquery is used as an element of an expression it must return exactly one value one column and one row Suppose that you decide that for any stock number you must charge a higher price tha
117. server and then transferred to the secondary server Applications can read data from either database server Thus the secondary site can provide a dual purpose It provides data protection and it provides improved performance for users at the secondary site who need to read but not write data If the primary server call it serverA fails for any reason the secondary server call it serverB can become an independent server Users who would normally use the primary serverA can be switched to serverB Service to all the users can continue with a minimum of disruption while the original primary server serverA is being repaired Data replication provides good data protection and continuity of service but it is expensive Memory must be provided for two complete copies of the data shipping the data to a remote site affects performance and manage ment requires the attention of the OnLine administrators on both sites Archives OnLine provides specialized tools for making archives Archives can be prepared locally or on a networked computer Archives should be stored in a location that is physically removed from the database server so it may be convenient to build the archives on a networked computer located at a different physical site Data Integrity for Distributed Data INFORMIX OnLine Dynamic Server allows you to update data in several databases on different database servers For example a purchase order a sin gle transaction
118. size of some tables is not known in advance e Tables can grow at different times and different rates e All the pages of a table should be adjacent for best performance Because table sizes are not known table space cannot be preallocated Therefore extents are added only as they are needed but all the pages in any one extent are contiguous for better performance Choosing Extent Sizes When you create a table you can specify the size of the first extent as well as the size of the extents to be added as the table grows You can change the size of added extents later with the ALTER TABLE statement The following partial example creates a table with a half megabyte initial extent and 100 kilobyte added extents CREATE TABLE big_one column specifications IN big_space EXTENT SIZE 512 NEXT SIZE 100 The following example changes the next extent size of the table to 50 kilobytes This has no effect on extents that already exist ALTER TABLE big_one MODIFY NEXT SIZE 50 10 8 Tuning Your Data Model INFORMIX OnLine Dynamic Server Disk Storage The next extent sizes of the following kinds of tables are not very important to performance e A small table has only one extent otherwise it would not be small If it is heavily used large parts of it are buffered in memory anyway e An infrequently used table is not important to performance no matter what size it is e A table that resides in a dedic
119. something unexpected goes wrong during a statement the database server returns a negative number in SQLCODE to explain the problem The meanings of these codes are documented in the Informix Error Messages manual and in the on line error message file Programming with SQL 5 11 Calling the Database Server The SQLERRD Array Some error codes that can be reported in SQLCODE reflect general problems and the database server can set a more detailed code in the second field of SQLERRD This second code referred to as the ISAM error reveals the low level error encountered by the database server I O routines or by the underlying operating system The integers in the array named SQLERRD are set to different values following different statements The first and fourth elements of the array are used only in INFORMIX 4GL INFORMIX ESQL C INFORMIX ESQL COBOL and INFORMIX ESQL FORTRAN The fields are used as shown in Figure 5 4 on page 5 9 These additional details can be very useful For example you can use the value in the third field to report how many rows were deleted or updated When your program prepares an SQL statement entered by the user and an error is found the value in the fifth field enables you to display the exact point of error to the user DB Access and INFORMIX SQL use this feature to position the cursor when you ask to modify a statement after an error The SQLAWARN Array The eight character fields in the SQLAWARN arra
120. specify one argument and the data type of that argument For example if a procedure needs to have a single piece of integer information passed to it you can provide a procedure heading as shown in the following example CREATE PROCEDURE safe_delete cnum INT Returning Results A procedure that returns one or more values must contain two lines of code to accomplish the transfer of information one line to state the data types that are going to be returned and one line to return the values explicitly Specifying Return Data Types Immediately after you specify the name and input parameters of your procedure you must include a RETURNING clause with the data type of each value you expect to be returned The following example shows the header of a procedure name parameters and RETURNING clause that expects one integer as input and returns one integer and one 10 byte character value CREATE PROCEDURE get_call cnum INT RETURNING INT CHAR 10 Creating and Using Stored Procedures 14 25 Passing Information into and out of a Procedure Returning the Value Once you use the RETURNING clause to indicate the type of values that are to be returned you can use the RETURN statement at any point in your proce dure to return the same number and data types as listed in the RETURNING clause The following example shows how you can return information from the get_call procedure CREATE PROCEDURE get_call cnum INT
121. statement The function in Figure 5 9 displays an error message if anything goes wrong As written it makes no distinction between an error from the PREPARE operation and one from the EXECUTE operation It does not attempt to interpret the numeric error code leaving it to the user to interpret SQL statements can be written into programs as if they were normal statements of the programming language Program variables can be used in WHERE clauses and data from the database can be fetched into them A preprocessor translates the SQL code into procedure calls and data structures Statements that do not return data or queries that return only one row of data are written like ordinary imperative statements of the language Que ries that can return more than one row are associated with a cursor that rep resents the current row of data Through the cursor the program can fetch each row of data as it is needed Static SQL statements are written into the text of the program However the program can form new SQL statements dynamically as it runs and execute them also In the most advanced cases the program can obtain information about the number and types of columns that a query returns and dynamically allocate the memory space to hold them Programming with SQL 5 37 Summary 5 38 Programming with SQL Modifying Data Through SQL Programs Chapter Overview 3 Using DELETE 3 Direct Deletions 4 Errors During Direct Deletions 4 Using
122. table the disk might have to seek across the entire width of the dbspace It is possible to rebuild a dbspace so that tables are compact once again as shown in Figure 10 5 The relative order of the reorganized tables within the dbspace is not important all that matters is that the pages of each reorganized table are together When reading a table sequentially no long seeks occur When reading a table nonsequentially the disk arm ranges only over the space occupied by that table E tabie1 a table 3 A dbspace reorganized to make tables compact Use the following steps to reorganize a dbspace 1 Copy the tables in the dbspace to tape individually using the onunload utility 2 Drop all the tables in the dbspace 3 Re create the tables using the onload utility The onload utility re creates the tables with the identical properties they had before including the same extent sizes When a new extent is created adjacent to the previous extent the two are treated as a single extent Tuning Your Data Model 10 11 Calculating Table Sizes You can also unload a table using the UNLOAD statement in DB Access INFORMIX SQL or INFORMIX 4GL and reload the table using the compan ion LOAD statement or the dbload utility However these operations convert the table into character form while onload and onunload work with binary copies of disk pages You can reorganize a single table in two more ways If you use the ALTER T
123. table 1 135 REFERENCES clause 1 215 ROW keyword 1 33S rules for primary key constraints rules for unique constraints 1 315 American National Standards Institute See ANSI AND keyword syntax in Condition segment 1 404S use in Condition segment 1 417S with BETWEEN keyword 1 327S AND logical operator 1 417S 2 36T ANSI 1 15T ANSI compliance determining 1 10R table naming 1 296S ANSI compliance ansi flag 4 15R Intro 7S 1 785 1 855 1 137S described 1 9R list of SQL statements 1 75 reserved words 1 470S updating rows 1 385S ANSI compliant database buffered logging restricted in 9 23T create with START DATABASE 1 376S description of 1 595 1 15T designating 1 10R effect on cursor behavior 1 13R decimal data type 1 13R default isolation level 1 13R escape characters 1 13R object privileges 1 12R owner naming 1 12R SQLCODE 1 14R transaction logging 1 12R transactions 1 11R FOR UPDATE not required in 1 1485 6 16T index naming 1 419S 1 484S 1 505S owner naming 1 12R privileges 1 12R procedure naming 1 495S reason for creating 1 9R Repeatable Read isolation standard in 7 13T signalled in SQLAWARN 5 12T SQL statements allowed 1 14R table privileges 1 855 11 7T using with INFORMIX SE 1 615 with BEGIN WORK 1 368 ANY keyword beginning a subquery 1 330S 3 34T in WHENEVER 1 398S use in Condition subquery 1 415S Application common features 1 18T description of 1 16T design of order entry 4 23T handling errors 5
124. the existence dependency for the relationship between the name and address entities mandatory An optional existence dependency could be indicated by a business rule that said a person may or may not have children Cardinality places a constraint on the number of times an entity can appear in a relationship The cardinality of a 1 1 relationship is always one But the cardinality of a 1 n relationship is open n could be any number If you need to place an upper limit on n you do it by specifying a cardinality for the rela tionship For example in a store sale example you could limit the number of sale items that a customer can purchase at one time You usually place cardi nality constraints through your application program or through stored procedures For additional information about cardinality see any entity relationship data modeling text References to two data modeling books are included in the Summary of this chapter Building Your Data Model 8 9 Identifying and Defining Your Principal Data Objects Discover the Relationships A compact way to discover the relationships is to prepare a matrix that names all the entities on the rows and again on the columns Figure 8 3 is a matrix that reflects the entities for the personal telephone directory name address number number number voice fax modem name address number voice number fax number modem Figure 8 3 A
125. the optimizer from using an index One or more of the ordered columns is not included in the index e The columns are named in a different sequence in the index and the ORDER BY or GROUP BY clause The ordered columns are taken from different tables Another way to avoid sorts is discussed in Using a Temporary Table to Speed Queries on page 13 36 If a sort is necessary look for ways to simplify it As discussed in Time Cost of a Sort on page 13 15 the sort is quicker if you can sort on fewer or narrower columns Eliminating Sequential Access to Large Tables Sequential access to a table other than the very first one in the plan is ominous it threatens to read every row of the table once for every row selected from the preceding tables You should be able to judge how many times that is perhaps a few but perhaps hundreds or even thousands If the table is small it can do no harm to read it repeatedly the table resides completely in memory Sequential search of an in memory table can be faster than searching the same table through an index especially if also having its index pages in memory pushes other useful pages out of the buffers When the table is larger than a few pages however repeated sequential access is deadly to performance One way to prevent this is to provide an index to the column being used to join the table The subject of indexing is discussed in the context of database design in Mana
126. the Connect privilege You can use table level privileges to deny access to confidential tables or columns Or you can use a stored procedure to provide limited access to confidential tables or columns In addition you can deny all access to tables and allow it only through views that do not expose confidential rows or columns 11 30 Granting and Limiting Access to Your Database Summary Controlling changes to data and database structure You safeguard the integrity of the data model by restricting grants of the Resource Alter References and DBA privileges You ensure that only authorized persons modify the data by controlling the grants of the Delete and Update privileges and by granting the Update privilege on as few columns as possible You ensure that consistent reasonable data is entered by granting the Insert privilege only on views that express logical constraints on the data Alternatively you can control the insertion and modification of data or the modification of the database itself by limiting access to constrictive stored procedures Granting and Limiting Access to Your Database 11 31 Summary 11 32 Granting and Limiting Access to Your Database Chapter Understanding Informix Networking Chapter Overview 3 What Is a Network 4 Database Management System Configurations 4 A Single User Configuration 4 Advantages and Disadvantages of a Single User System 6 A Local Multiuser Configuration 6 Advantage
127. the alteration in progress at the time of failure is lost CREATE DATABASE a_logged_db WITH LOG IN a log file You must specify a file to contain the transaction log The form of the file name depends on the rules of your operating system This file grows whenever the database is altered Whenever the database files are archived you should set the log file back to an empty condition so it reflects only transactions following the latest archive Implementing Your Data Model 9 23 Creating the Database e ANSI compliant logging This is the same as regular logging but the ANSI rules for transaction processing are also enabled See the discussion of ANSI compliant databases in Chapter 1 of the Informix Guide to SQL Ref erence CREATE DATABASE std_rules_db WITH LOG IN a log file MODE ANSI You can add a transaction log to a nonlogged database later using the START DATABASE statement Using CREATE TABLE Use the CREATE TABLE statement to create each table you designed in the data model This statement has a complicated form but it is basically a list of the columns of the table For each column you supply the following information The name of the column e The data type from the domain list you made e If the column or columns is a primary key the constraint PRIMARY KEY e If the column or columns is a foreign key the constraint FOREIGN KEY e If the column is not a primary key and should not allow n
128. the deletion is put in the file updates CREATE DBA PROCEDURE delete_customer cnum INT DEFINE username CHAR 8 DELETE FROM customer WHERE customer_num cnum IF username acctclrk THEN SYSTEM echo Delete from customer by acctclrk gt gt mis records updates ENF IF END PROCEDURE Figure 11 5 A procedure to delete rows and record changes made by a certain user You can monitor all the deletions made through the procedure by removing the IF statement and making the SYSTEM statement more general If you change the procedure in Figure 11 6 to record all deletions it looks like the procedure in Figure 11 6 CREATE DBA PROCEDURE delete_customer cnum INT DEFINE username CHAR 8 LET username USER DELETE FROM tbname WHERE customer_num cnum SYSTEM echo Deletion made from customer table by username gt gt hr records deletes END PROCEDURE Figure 11 6 Stored procedure to delete rows and record user Restricting Object Creation To put restraints on what and how objects are built use stored procedures within the following setting e You are the DBA of the database e All the other users have the Connect privilege to the database They do not have the Resource privilege e Your stored procedure or set of stored procedures is created using the DBA keyword 11 18 Granting and Limiting Access to Your Database Using Views e Your stored procedure or set of stored procedures crea
129. the rows in the actual tables from which the active set rows are derived can change If they do some of the active set rows no longer reflect the current table contents These ideas may seem unsettling at first but as long as your program only reads the data there is no such thing as stale data or rather all data is equally stale No matter when it is taken the active set is a snapshot of the data as it is at one moment in time A row is different the next day it does not matter if itis also different in the next millisecond To put it another way no practical difference exists between changes that occur while the program is running and changes that are saved and applied the instant the program terminates The only time that stale data can cause a problem is when the program intends to use the input data to modify the same database for example when a banking application must read an account balance change it and write it back Chapter 6 Modifying Data Through SQL Programs discusses programs that modify data Using a Cursor A Parts Explosion When you use a cursor supplemented by program logic you can solve prob lems that plain SQL cannot solve One of these is the parts explosion problem sometimes called Bill of Materials processing At the heart of this problem is a recursive relationship among objects one object contains other objects which contain yet others The problem is usually stated in terms of a manufactu
130. the vendor_name field is 32 bytes long the output table has about 95 rows per page and occupies about 160 pages These pages are written and then sorted causing 5x160 800 page reads and writes Thus this query reads or writes 892 pages in all Now join its output to part for the final result which is shown in the following example SELECT pvvn_by_pn x part part_desc FROM pvvn_by_pn part WHERE pvvn_by_pn part_num part part_num DROP TABLE pvvn_by_pn This query reads pvvn_by_pn sequentially 160 pages It accesses part by way of its index 15 000 times but again the keys are presented in part_num sequence so the result is to read part sequentially 400 pages through its index 20 pages The output is produced in sorted order By splitting the query into three steps and by substituting sorts for indexed access a query that read 50 400 pages is converted into one that reads and writes approximately 1 772 pages a 30 to 1 ratio Note Informix database servers earlier than version 4 1 do not permit you to use the ORDER BY and INTO TEMP clauses in the same query With these database servers you can achieve the preceding solution by selecting INTO TEMP without ordering then applying the desired ordering through a clustered index The improvement is at most 15 1 rather than of 30 1 Poor performance can come from several sources not solely the SQL opera tions in a program Before you focus your attention on the code ta
131. theoretical correctness in the data model Before you make the change be sure it returns a reasonable savings in disk space or execution time Moving Strings to a Companion Table Strings less than half a page long waste disk space if you treat them as TEXT but you can remove them from the main table to a companion table The use of companion tables is the subject of the next section Splitting Wide Tables Consider all the attributes of an entity whose rows are too wide for good performance Look for some theme or principle on which they can be divided into two groups Split the table into two a primary table and a companion table repeating the primary key in each one The shorter rows allow each table to be queried or updated more quickly Division by Bulk One principle on which you can divide an entity table is bulk Move the bulky attributes which are usually character strings to the companion table Keep the numeric and other small attributes in the primary table In the dem onstration database you can split the ship_instruct column from the orders table You can call the companion table orders_ship It has two columns a primary key that is a copy of orders order_num and the original ship_instruct column Division by Frequency of Use Another principle for division of an entity is frequency of use If a few attributes are rarely queried they can be moved out to a companion table In the demonstration database it could be t
132. they are to be performed in relation to the triggering statement You have the following choices e Before the triggering statement executes e After the triggering statement executes e For each row that is affected by the triggering statement A single trigger can define actions for each of these times You define a triggered action by specifying when it occurs and then providing the SQL statement or statements to execute You specify when the action is to occur with the keywords BEFORE AFTER or FOR EACH ROW The triggered actions follow enclosed in parentheses The following triggered action definition specifies that the stored procedure upd_items_p1 is to be executed before the triggering statement BEFORE EXECUTE PROCEDURE upd_items_p1 a BEFORE action A Complete CREATE TRIGGER Statement If you combine the trigger name clause the trigger event clause and the triggered action clause you have a complete CREATE TRIGGER statement The following CREATE TRIGGER statement is the result of combining the components of the statement from the preceding examples This trigger executes the stored procedure upd_items_p1 whenever the quantity column of the items table is updated CREATE TRIGGER upqty UPDATE OF quantity ON items BEFORE EXECUTE PROCEDURE upd_items_p1 Note that if a database object in the trigger definition such as the stored procedure upd_items_p1 in this example does not exist when
133. to insert into a temporary table Then select from that table in the INSERT statement The following statements are required to accomplish this SELECT stock_num HSK temp_manu description unit_price 2 half_price unit unit_descr FROM stock WHERE manu_code ANZ AND stock_num lt 110 INTO TEMP anzrows INSERT INTO stock SELECT FROM anzrows DROP TABLE anzrows This SELECT statement takes existing rows from stock and substitutes a literal value for the manufacturer code and a computed value for the unit price These rows are then saved in a temporary table anzrows which is immedi ately inserted into the stock table When you insert multiple rows a risk exists that one of the rows contains invalid data that might cause the database server to report an error When this happens the statement terminates early Even if no error occurs a very small risk exists that there might be a hardware or software failure while the statement is executing for example the disk might fill up In either event you cannot easily tell how many new rows were inserted If you repeat the statement in its entirety you might create duplicate rows or you might not Because the database is in an unknown state you cannot know what to do The answer lies in using transactions as discussed in Interrupted Modifications on page 4 22 Updating Rows You use the UPDATE statement to change the contents of one or more columns
134. to not wait return locktype If the database server does not support the SET LOCK MODE statement your program is effectively always in NOT WAIT mode that is whenever it tries to lock a row that is locked by another program it receives an error code immediately 7 16 Programming for a Multiuser Environment Locking with Other Database Servers Isolation While Reading Informix database servers other than INFORMIX OnLine Dynamic Server do not normally place locks when fetching rows Nothing comparable exists to the shared locks used by OnLine to implement the Cursor Stability isolation level If your program fetches a row with a singleton SELECT statement or through a cursor that is not declared FOR UPDATE the row is fetched immediately regardless of whether it is locked or modified by an unfinished transaction This design produces the best performance especially when locks are implemented by writing notes in disk files but you must be aware that the program can read rows that are modified by uncommitted transactions You can obtain the effect of Cursor Stability isolation by declaring a cursor FOR UPDATE and then using it for input Whenever the database server fetches a row through an update cursor it places a lock on the fetched row If the row is already locked the program waits or receives an error depending on the lock mode When the program fetches another row without updating the current one the lock on the
135. tony is rejected as an error 11 26 Granting and Limiting Access to Your Database Privileges and Views You can use the WITH CHECK OPTION feature to enforce any kind of data constraint that can be stated as a Boolean expression In the following exam ple you can create a view of a table in which all the logical constraints on data are expressed as conditions of the WHERE clause Then you can require all modifications to the table to be made through the view CREATE VIEW order_insert AS SELECT FROM orders O WHERE order_date TODAY no back dated entries AND EXISTS ensure valid foreign key SELECT FROM customer C WHERE O customer_num C customer_num AND ship_weight lt 1000 reasonableness checks AND ship_charge lt 1000 WITH CHECK OPTION Because of EXISTS and other tests all of which are expected to be successful when retrieving existing rows this is a most inefficient view for displaying data from orders However if insertions to orders are made only through this view and you are not already using integrity constraints to constrain data it is impossible to insert a back dated order an invalid customer number or an excessive shipping weight and shipping charge Privileges and Views When you create a view the database server tests your privileges on the underlying tables and views When you use a view only your privileges with regard to the view are tested Privileges When Creating a View When y
136. total of three or four page accesses per index When you insert a row its entries must be inserted in all indexes The place for entry of the inserted row must be found two or three pages in and rewritten one page out for a total of three or four page accesses per index e When you update a row its entries must be looked up in each index that applies to a column that was altered two or three pages in The leaf page must be rewritten to eliminate the old entry one page out then the new 10 20 Tuning Your Data Model Managing Indexes column value must be located in the same index two or three more pages in and the row entered one more page out Insertions and deletions change the number of entries on a leaf page In virtually every pagents operation some additional work must be done because a leaf page has either filled up or been emptied However because pagents is usually greater than 100 this occurs less than 1 percent of the time and can be disregarded for estimating In short when a row is inserted or deleted at random allow three to four added page I O operations per index When a row is updated allow six to eight page I O operations for each index that applies to an altered column Bear in mind also that if a transaction is rolled back all this work must be undone For this reason rolling back a transaction can take a long time Because the alteration of the row itself requires only two page I O operati
137. use in expression 1 456S WHEN condition in triggered action 1 122S restrictions 1 122S use of 1 122S WHENEVER statement syntax and use 1 398S WHERE clause subscripting 2 44T WHERE CURRENT OF clause impact on trigger 1 1125 WHERE CURRENT OF keywords syntax in DELETE 1 159S in UPDATE 1 383S use in DELETE 6 7T in UPDATE 1 390S 6 15T WHERE keyword Boolean expression in 2 36T comparison condition 2 29T to 2 45T date oriented functions in 2 60T enforcing data constraints 11 27T host variables in 5 14T in DELETE 4 4T to 4 6T joining tables 1 331S null data tests 2 35T prevents use of index 13 32T 13 33T 13 35T range of values 2 32T relational operators 2 29T selecting rows 2 28T setting descriptions of items 1 354S subqueries in 3 33T syntax in DELETE 1 159S Index 49 50 Index in SELECT 1 310S in UPDATE 1 383S testing a subscript 2 44T use in DELETE 1 160S in UPDATE 1 388S with a subquery 1 326S with ALL keyword 1 330S with ANY keyword 1 330S with BETWEEN keyword 1 327S with IN keyword 1 327S with IS keyword 1 3275 with LIKE keyword 1 328S with MATCHES keyword 1 3285 with NOT keyword 2 32T with OR keyword 2 33T with relational operator 1 3265 with SOME keyword 1 330S wildcard comparisons 2 37T See also Condition segment WHILE keyword in CONTINUE statement 2 68 in EXIT 2 148 WHILE statement looping in a stored procedure 14 23T syntax 2 468 with NULL expressions 2 465 Wildcard character asterisk 2 1
138. variable 4 27R Date representing with NLS 1 15R DAY function as time function 2 57T syntax in expression 1 454S use as time function 2 56T in expression 1 455S DAY keyword syntax in DATETIME data type 1 4285 in INTERVAL data type 1 485S use as DATETIME field qualifier 3 8R 1 488S as INTERVAL field qualifier 3 14R 1 491S DBA keyword in GRANT 1 233S in REVOKE 1 303S DB Access creating database with 5 34T 9 26T UNLOAD statement 9 28T DBANSIWARN environment variable 4 15R 1 785 1 85S 1 137S 5 10T DBAPICODE environment variable 1 16R 4 47R relation to crtcmap utility 5 5R DBA privileged procedure 14 13T DBA See Database Administrator DBDATE environment variable 4 16R 4 8T 9 13T DBDELIMITER environment variable 4 18R 1 258S DBEDIT environment variable 4 18R dbexport utility description of 5 8R destination options 5 10R Interrupt key 5 9R specifying field delimiter with DBDELIMITER 4 18R unloading a database 5 8R using with NLS 5 12R dbimport utility create options 5 16R creating a database 5 14R description of 5 13R input file location options 5 15R Interrupt key 5 14R using with NLS 5 13R 5 18R DBINFO function syntax in expression 1 448S use in expression 1 4485 DBLANG environment variable 4 19R dbload utility creating a command file 5 23R description of 5 19R INSERT statement compared to SQL INSERT statement 5 30R Interrupt key 5 21R loading data from a command file 5 20R loading data into a ta
139. watches ANZ watches item 304 instead of 6 Parmelee Olympic City 415 534 8822 992 11 28 13 34 Received plain white swim caps 313 ANZ of navy with team logo 313 SHM instead 6 Parmelee Olympic City 415 534 8822 992 12 21 11 24 Second complaint from this customer two cases right handed outfielder gloves instead of one case lefties Received 1 HRO Composing Advanced SELECT Statements 3 23 Creating Advanced Joins Simple Outer Join on Two Tables Query 3 22 uses the same select list tables and comparison condition as the preceding example but this time it creates a simple outer join SELECT c customer_num c lname c company c phone u call_dtime u call_descr FROM customer c OUTER cust_calls u WHERE c customer_num u customer_num Query 3 22 The addition of the keyword OUTER in front of the cust_calls table makes it the subservient table An outer join causes the query to return information on all customers whether or not they have made calls to customer service All rows from the dominant customer table are retrieved and null values are assigned to corresponding rows from the subservient cust_calls table 3 24 Composing Advanced SELECT Statements customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone cal
140. which can contain occurrences of b300 b1200 and b2400 Figure 8 16 shows the data model normalized through first normal form name child rec_num PK rec_num FK Iname O lt child_name address fname id_num PK bdate O rec_num FK anniv gt street email city es state zipcode voice Q faxname vce_num PK fax_num PK FK rec_num rec_num PK FK vce_type modem mdm_num PK fax rec_num FK fax_num PK b_type operfrom opertill Figure 8 16 The data model of a personal telephone directory Second Normal Form An entity is in second normal form if it is in first normal form and all its attributes depend on the whole primary key In relational terms this means that every column in a table must be functionally dependent on the whole pri mary key of that table Functional dependency indicates that a link exists between the values in two different columns To say that the value of an attribute depends on a column means that if the value in the column changes the value of the attribute must also change The attribute is a function of the column The following explanations make this more specific e Ifthe table has a one column primary key the attribute must depend on that key If the table has a composite primary key the attribute must depend on the values in all of its columns taken as a whole not on just one or some of them Building Your Data Model 8
141. write programs that perform them This chapter is only an introduction to the concepts that are common to SQL programming in any language Before you can write a successful program in a particular programming language you must first become fluent in that lan guage Then because the details of the process are slightly different in every language you must become familiar with the manual for the Informix SQL API specific to that language SQL in Programs You can write a program in any of several languages and mix SQL statements in among the other statements of the program just as if they were ordinary statements of that programming language The SQL statements are said to be embedded in the program and the program is said to contain embedded SQL often abbreviated by Informix as ESOL Programming with SQL 5 3 SQL in Programs Informix produces SQL APIs for the following programming languages ec COBOL FORTRAN pre version 6 0 e Ada version 4 0 only All SQL APIs products work in a similar way as shown in Figure 5 1 You write a source program in which you treat SQL statements as executable code Your source program is processed by an embedded SQL preprocessor a pro gram that locates the embedded SQL statements and converts them into a series of procedure calls and special data structures gt AN ESQL source program Figure 5 1 AN Ke ESQL Source program Language Executable preprocessor wit
142. you to move a table to a different database or even to a different computer while leaving your queries the same Suppose you have several queries that refer to the tables customer and orders The queries are embedded in programs forms and reports The tables are part of database stores6 which is kept on database server avignon Now the decision is made that the same programs forms and reports are to be made available to users of a different computer on the network database server nantes Those users have a database that contains a table named orders containing the orders at their location but they need access to the table customer at avignon To those users the customer table is external Does this mean you must pre pare special versions of the programs and reports versions in which the customer table is qualified with a database server name A better solution is to create a synonym in the users database as shown in the following example DATABASE stores6 nantes CREATE SYNONYM customer FOR stores6 avignon customer When the stored queries are executed in your database the name customer refers to the actual table When they are executed in the other database the name is translated through the synonym into a reference to the external table Synonym Chains To continue the preceding example suppose that a new computer is added to your network Its name is db_crunch The customer table and other tables are mo
143. you want users to read only the name address and telephone number of a customer you can modify the procedure as shown in Figure 11 3 CREATE DBA PROCEDURE read_customer cnum INT RETURNING CHAR 15 CHAR 15 CHAR 18 DEFINE p_lname p_fname CHAR 15 DEFINE p_phone CHAR 18 SELECT fname lname phone INTO p_fname p_lname p_phone FROM customer WHERE customer_num cnum RETURN p_fname p_lname p_phone END PROCEDURE Figure 11 3 Stored procedure to restrict reads on customer data Restricting Changes to Data Using stored procedures you can restrict changes made to a table Simply channel all changes through a stored procedure The stored procedure makes the changes rather than users making the changes directly If you want to 11 16 Granting and Limiting Access to Your Database Figure 11 4 Controlling Access to Data Using Stored Procedures limit users to deleting one row at a time to ensure that they do not accidentally remove all the rows in the table set up the database with the following privileges e You are the DBA of the database e All the users have the Connect privilege to the database They may or may not have the Resource privilege They do not have the Delete for this example privilege on the table being protected e Your stored procedure is created using the DBA keyword e Your stored procedure performs the deletion Write a stored procedure similar to the one shown in Figure 11 4
144. 0 DISPLAY o_num i_num s_num FETCH the_item D WHILE tl Z In this version the case of zero returned rows is handled early so no second test of sqlcode exists within the loop These versions have no measurable dif ference in performance because the time cost of a test of sqlcode is a tiny fraction of the cost of a fetch Locating the INTO Clause The INTO clause names the host variables that are to receive the data returned by the database server It must appear in either the SELECT or the FETCH statement but not both The following example is reworked to specify host variables in the FETCH statement DECLARE the_item CURSOR FOR SELECT order_num item_num stock_num FROM items OPEN the_item WHILE status 0 FETCH the_item INTO o_num i_num s_num IF status 0 THEN DISPLAY o_num i_num s_num END IF END WHILE The second form has the advantage that different rows can be fetched into different variables For example you can use this form to fetch successive rows into successive elements of an array 5 22 Programming with SQL Retrieving Multiple Rows Cursor Input Modes For purposes of input a cursor operates in one of two modes sequential or scrolling A sequential cursor can fetch only the next row in sequence so it can read through a table only once each time it is opened A scroll cursor can fetch the next row or any prior row so it can read rows multiple times The followi
145. 0 27T replacing with VARCHAR 10 26T subscripting 2 44T substrings of 2 27T syntax 1 425S truncation signalled 5 12T using as default value 1 195 1 89S versus NCHAR data type 1 19R CHARACTER data type See CHAR data type Character mapping files 5 5R Character string as DATE values 3 29R as DATETIME values 3 10R 3 29R as INTERVAL values 3 15R processing with NLS 1 15R See also Quoted String segment Character position form of FILE and INSERT statements 5 28R Check constraint adding with ALTER TABLE 1 255 definition of 1 985 4 19T specifying at column level 1 985 specifying at table level 1 98S CHECK keyword use in ALTER TABLE 1 255 use in CREATE TABLE 1 985 CHECK TABLE statement syntax and use 1 375 Checking contents of environment configuration file 5 4R Checking for corrupted tables 1 375 chkenv utility description of 5 4R error message for 5 4R Chunk description of 10 4T mirrored 10 5T Client server environment 1 133S CLOSE DATABASE statement effect on database locks 7 7T prerequisites to close 1 415 syntax 1 415 CLOSE statement Index 5 6 Index closing a select cursor 1 385 closing an insert cursor 1 39S cursors affected by transaction end 1 405 syntax 1 385 with concatenation operator 1 432S CLUSTER keyword syntax in ALTER INDEX 1 12S in CREATE INDEX 1 635 use in ALTER INDEX 1 128 in CREATE INDEX 1 645 Clustered index creating with CREATE INDEX 1 645 description of 10 25T with ALTER INDEX 1 125 wi
146. 0 L04 940 116 940 110 940 114 940 106 940 108 940 L17 940 L11 940 L01 940 L09 941 L02 943 L03 943 L07 946 118 Query Result 2 20 Using the WHERE Clause Perhaps you want to see only those orders placed by a particular customer or the calls entered by a particular customer service representative You can add a WHERE clause to a SELECT statement to retrieve these specific rows from a table You can use the WHERE clause to set up a comparison condition or a join condition This section demonstrates only the first use Join conditions are described in a later section and in the next chapter 2 28 Composing Simple SELECT Statements Single Table SELECT Statements The set of rows returned by a SELECT statement is the active set for that statement A singleton SELECT statement returns a single row In INFORMIX 4GL or an SQL API the retrieval of multiple rows requires the use of a cursor See Chapter 5 Programming with SQL and Chapter 6 Modifying Data Through SQL Programs Creating a Comparison Condition Figure 2 2 The WHERE clause of a SELECT statement specifies the rows you want to see A comparison condition employs specific keywords and operators to define the search criteria For example you might use one of the keywords BETWEEN IN LIKE or MATCHES to test for equality or the keywords IS NULL to test for null values You can combine the keyword NOT with any of these keywords to specify the opposite condi
147. 00 256 50 2 1004 1 126 00 132 50 3 1004 1 240 00 246 50 4 1004 1 800 00 806 50 1 1021 2 75 00 81 50 2 1021 3 225 00 231 50 3 1021 3 690 00 696 50 4 1021 2 624 00 630 50 1 1022 1 40 00 46 50 2 1022 2 96 00 102 50 3 1022 2 96 00 102 50 1 1023 2 40 00 46 50 2 1023 2 116 00 122 50 3 1023 1 80 00 86 50 4 1023 1 228 00 234 50 3 1023 1 170 00 176 50 6 1023 1 190 00 196 50 Query Result 2 38 2 48 Composing Simple SELECT Statements Single Table SELECT Statements Query 2 39 calculates and displays in an expression column if you are using DB Access or INFORMIX SQL the interval between when the customer call was received call_dtime and when the call was resolved res_dtime in days hours and minutes SELECT customer_num user_id call_code call_dtime res_dtime call_dtime FROM cust_calls ORDER BY user_id Query 2 39 customer_num user_id call_code call_dtime expression 116 mannyn I 1992 12 21 11 24 5 20 55 116 mannyn I 1992 11 28 13 34 0 03 13 106 maryj D 1993 06 12 08 20 0 00 05 121 maryj 0 1993 07 10 14 05 0 00 01 127 maryj I 1993 07 31 14 30 110 riche L 1993 07 07 10 24 0 00 06 119 riche B 1993 07 01 15 00 0 17 21 Query Result 2 39 Using Display Labels You can assign a display label to a computed or derived data column to replace the default column header expression In Query Result 2 37 Query Result 2 38 and Query Result 2 39 the derived data is shown in a column cal
148. 07 10 24 20 Jewell 017 07 09 1993 1 Keyes 009 06 14 1993 2 Lawson 006 05 30 1993 09 Miller 28 Moore 26 Neelie 022 07 24 1993 22 O Brian 019 07 11 1993 6 Parmelee 005 05 24 1993 1992 12 21 11 24 6 Parmelee 005 05 24 1993 1992 11 28 13 34 01 Pauli 002 05 21 1993 24 Putnum 021 07 23 1993 08 Quinn 07 Ream 02 Sadler 27 Satifer 023 07 24 1993 1993 07 31 14 30 19 Shorter 016 06 29 1993 1993 07 01 15 00 17 Sipes 007 05 31 1993 17 Sipes 012 06 18 1993 05 Vector 21 Wallack 018 07 10 1993 1993 07 10 14 05 06 Watson 004 05 22 1993 1993 06 12 08 20 06 Watson 014 06 25 1993 1993 06 12 08 20 Query Result 3 25 Note that if Query 3 25 had tried to create a join condition between the two subservient tables o and x as shown in Query 3 26 an error message would have indicated the creation of a two sided outer join WHERE o customer_num x customer_num Query 3 26 Composing Advanced SELECT Statements 3 31 Subqueries in SELECT Statements Subqueries in SELECT Statements 3 32 A SELECT statement nested in the WHERE clause of another SELECT statement or in an INSERT DELETE or UPDATE statement is called a subquery Each subquery must contain a SELECT clause and a FROM clause and it must be enclosed in parentheses which tells the database server to perform that operation first Subqueries can be correlated or uncorrelated A subquery or inner SELECT statement is correlated when the value it produces depends on a value
149. 1 code numbers del_rowcnt sqlca sqlerrd 2 and count of rows if del_result lt 0 some problem exec sql rollback work put everything back else everything worked OK exec sql commit work finish transaction An important point in this example is that the program saves the important return values in the SQLCA before it ends the transaction The reason is that both the ROLLBACK WORK and COMMIT WORK statements as with all SOL statements set return codes in the SQLCA Executing a ROLLBACK WORK statement after an error wipes out the error code unless it was saved it cannot be reported to the user The advantage of using transactions is that no matter what goes wrong the database is left in a known predictable state No question remains about how much of the modification is completed either all of it is or none of it is Modifying Data Through SQL Programs 6 5 Using DELETE Coordinated Deletions Figure 6 1 The usefulness of transaction logging is particularly clear when you must modify more than one table For example consider the problem of deleting an order from the demonstration database In the simplest form of the prob lem you must delete rows from two tables orders and items as shown in the INFORMIX 4GL example in Figure 6 1 WHENEVER ERROR CONTINUE do not terminate on error BEGIN WORK start transaction DELETE FROM items WHERE order _num o_num IF s
150. 10 25T composite 13 31T creating with CREATE INDEX 1 625 disk space used by 10 16T 10 20T 13 34T displaying information for 1 242S dropping 10 24T dropping with DROP INDEX 1 174S duplicate entries 10 16T 10 22T effect of physical order 13 27T in GROUP BY 13 10T in ORDER BY 13 10T locks table 7 7T managing 10 19T naming conventions 1 419S 1 469S 1 484S 1 505S optimizer 13 29T optimizer uses 13 9T 13 10T 13 26T ordering columns in composite 13 31T performance effects 13 18T sharing with constraints 1 86S sorting with NLS 1 15R time cost of 10 20T updating affects 13 31T utility to test or repair 13 31T when not used by optimizer 13 32T 13 33T 13 35T with temporary tables 1 343S INDEX keyword syntax in GRANT 1 235S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 302S Index Name segment syntax 1 4195 1 495S use 1 504S Index privilege 1 236S 11 8T INDEXES FOR keywords in INFO statement 1 242S Indexes with dbload utility 5 21R INDICATOR field setting with SET DESCRIPTOR 1 358S INDICATOR keyword in SELECT 1 3195 1 320S 1 3215 1 432S Indicator variable definition of 5 15T in EXECUTE 1 186S in expression 1 467S in SELECT 1 319S 1 3208 1 3215 1 4325 using non English characters in 1 22R INFO statement displaying privileges and status 1 2425 displaying tables columns and indexes 1 2415 syntax 1 241S informix environment configuration file 4 4R privileges associated with user 1 234S
151. 13602 Hammerle Greta 13604 LaFor t Jean No l 13610 LeMa tre H lo se 13613 Llanero Gloria Dolores 13603 Monta a Jos Antonio 13611 Oatfield Emily 13605 Otker Hans J rgen 13614 verst Per Anders 13609 Tiramis Paolo Alfredo Query Result 2 19b Query Result 2 19b indicates that with the appropriate NLS environment variable settings names starting with foreign characters lesund taix tker and verst are collated differently than they are in the standard ASCII order so they are integrated in the list It does not distinguish between uppercase and lowercase letters Selecting Substrings You can select part of the value of a CHARACTER column by including a substring in the select list Suppose your marketing department is planning a mailing to your customers and wants a rough idea of their geographical distribution based on zip codes You could write a query similar to Query 2 20 SELECT zipcode 1 3 customer_num FROM customer ORDER BY zipcode Query 2 20 Composing Simple SELECT Statements 2 27 Single Table SELECT Statements Query 2 20 uses a substring to select the first three characters of the zipcode column which identify the state and the full customer_num and lists them in ascending order by zip code as shown in Query Result 2 20 zipcode customer_num 021 L25 080 L19 085 22 198 21 322 123 604 L27 740 L24 802 126 850 128 850 L20 940 LOS 940 12 940 13 940 L15 94
152. 16T performance analysis of 13 5T report generator 1 17T screen forms 1 17T Archives with INFORMIX SE 12 19T Archiving description of 1 10T 4 25T INFORMIX OnLine Dynamic Server methods 4 26T transaction log 4 26T ARC_DEFAULT environment variable 4 14R ARC_KEYPAD environment variable 4 14R Arithmetic functions See Algebraic functions Arithmetic operator in expression 1 4315 2 46T Array moving rows into with FETCH 1 199S AS keyword in SELECT 1 312S syntax in CREATE VIEW 1 136S in GRANT 1 231S use in CREATE VIEW 1 137S in GRANT 1 239S with display labels 1 316S with table aliases 1 325S ASC keyword syntax in CREATE INDEX 1 638 in SELECT 1 337S use in CREATE INDEX 1 668 in SELECT 1 338S Index 3 4 Index Ascending order in SELECT 2 14T ASCII collating order 1 15R 1 501S ASIN function syntax in expression 1 458S use in expression 1 460S Asterisk wild card character in SELECT 2 12T Asterisk arithmetic operator 1 431S use in SELECT 1 312S At sign in database name 1 421S ATAN function syntax in expression 1 458S use in expression 1 460S ATAN2 function syntax in expression 1 458S use in expression 1 461S Attribute identifying 8 14T important qualities of 8 15T nondecomposable 8 15T Audit trail applying with RECOVER TABLE 292S dropping with DROP AUDIT 1 171S manipulating audit trail file 1 293S no clustered index 1 64S starting with CREATE AUDIT 1 558 Automatic type conversion S
153. 1993 009 20 40 06 21 1993 005 80 80 06 09 1993 0 0 40 07 03 1993 005 80 80 06 09 1993 020 4 00 07 16 1993 005 80 80 06 09 1993 022 5 00 07 30 1993 012 70 80 06 29 1993 0 0 40 07 03 1993 012 70 80 06 29 1993 020 4 00 07 16 1993 013 60 80 07 10 1993 0 0 40 07 03 1993 017 60 00 07 13 1993 0 0 40 07 03 1993 018 70 50 07 13 1993 0 0 40 07 03 1993 Query Result 3 9 Suppose you want to select the results of a self join into a temporary table You would of course append an INTO TEMP clause to the SELECT statement However because you are in effect creating a new table you also must rename at least one set of column names by assigning them display labels Otherwise you get an error message that indicates duplicate column names and the temporary table is not created 3 12 Composing Advanced SELECT Statements Creating Advanced Joins Query 3 10 which is similar to Query 3 9 labels all columns selected from the orders table and puts them in a temporary table called shipping SELECT x order_num ordersl x ship_date shipl y po_num purch2 X po_num purchl y order_num orders2 FROM orders x orders y WHERE x ship_weight gt 5 y ship_weight ORDER BY ordersl AND x ship_date IS NOT NULI AND y ship_date IS NOT NULI Li orders2 INTO TEMP shipping Li y ship_date ship2 Query 3 10 If you SELECT from that table you see the rows in Query Result 3 10 ord
154. 20T selection 2 5T Relational operation 2 5T Relational operator BETWEEN 2 32T equals 2 30T EXISTS 3 33T IN 3 33T in a WHERE clause 2 29T to 2 45T in Condition segment 1 405S LIKE 2 37T NOT 2 32T NULL 2 35T OR 2 33T segment 1 500S with WHERE keyword in SELECT 1 326S Relationship attribute 8 15T cardinality 8 9T 8 13T complex 8 28T connectivity 8 8T 8 11T defining in data model 8 8T entity 8 5T existence dependency 8 9T mandatory 8 9T many to many 8 9T 8 11T many to many resolving 8 26T one to many 8 9T 8 11T one to one 8 9T 8 11T optional 8 9T recursive 8 28T redundant 8 29T using matrix to discover 8 10T RELATIVE keyword syntax in FETCH 1 1945 use in FETCH 1 196S Relay Module SQLRM environment variable 4 42R SQLRMDIR environment variable 4 43R Release notes Intro 9R Intro 115S 6T Remote database server 12 8T RENAME COLUMN statement restrictions 1 2945 syntax 1 294S RENAME TABLE statement ANSI compliant naming 1 296S syntax 1 296S REPAIR TABLE statement syntax and use 1 299S Repeatable Read isolation level description of 1 367S 7 12T emulating during update 1 202S REPEATABLE READ keywords syntax in SET ISOLATION 1 366S Replication of data 12 19T Report generator 1 17T Reserved words 1 470S Resolution in UPDATE STATISTICS 1 396S 1 397S with data distributions 1 396S RESOURCE keyword use in GRANT 1 233S use in REVOKE 1 303S Resource manager 12 11T Resource privilege 1 233S 11 7T 13 34T
155. 24 Updating a View 24 Inserting intoa View 25 Using WITH CHECK OPTION 25 Privileges and Views 27 Privileges When Creating a View 27 Privileges When Using a View 28 Summary 30 11 2 Granting and Limiting Access to Your Database Chapter Overview In some databases all data is accessible to every user In others this is not the case some users are denied access to some or all of the data You can restrict access to data at the following levels which are the subject of this chapter When the database is stored in operating system files you can sometimes use the file permission features of the operating system This level is not available when INFORMIX OnLine Dynamic Server holds the database It manages its own disk space and the rules of the operating system do not apply You can use the GRANT and REVOKE statements to give or deny access to the database or to specific tables and you can control the kinds of uses that people can make of the database You can use the CREATE PROCEDURE statement to write and compile a stored procedure that controls and monitors which users can read modify or create database tables You can use the CREATE VIEW statement to prepare a restricted or modified view of the data The restriction can be vertical excluding certain columns or horizontal excluding certain rows or both You can combine GRANT and CREATE VIEW statements to achieve precise control over the parts of a table a user can modif
156. 2T Wildcard characters with LIKE or MATCHES 1 498S Wildcard comparison in WHERE clause 2 37T to 2 44T WITH APPEND keywords in the SET DEBUG FILE TO statement 1 351S WITH CHECK keywords syntax in CREATE VIEW 1 136S use in CREATE VIEW 1 138S WITH CHECK OPTION keywords 11 25T WITH GRANT keywords syntax in GRANT 1 231S use in GRANT 1 237S WITH HOLD keywords declaring a hold cursor 7 19T 10 34T syntax in DECLARE 1 145S use in DECLARE 1 1508 1 157S WITH keyword syntax in CREATE DATABASE 1 57S WITH LISTING IN keywords warnings in a stored procedure 14 8T WITH LOG IN keywords syntax in START DATABASE 1 376S WITH MAX keywords relationship with COUNT field 1 354S WITH NO LOG keywords syntax in CREATE TABLE 1 848 in SELECT 1 341S use in CREATE TABLE 1 1045 in SELECT 1 343S WITH NO LOG keywords syntax in START DATABASE 1 376S WITH RESUME keywords in RETURN 2 395 WITHOUT HEADINGS keywords in the OUTPUT statement 1 271S WORM drive 12 6T Write once read many times device See WORM drive Writing a dbload command file in character position form 5 31R in delimiter form 5 26R X X Open and Informix implementation of NLS 1 15R setting NLS environment variables 4 43R setting the LC_COLLATE category 4 50R setting the LC_CTYPE category 4 51R setting the LC_MONETARY category 4 52R setting the LC_NUMERIC category 4 53R setting the LC_TIME category 4 53R specifications icon for Intro 8S X Open mode FETCH statement 1 195S GE
157. 31 Normalizing Your Data Model Ifthe attribute also depends on other columns these must be columns of a candidate key that is columns that are unique in every row If you do not convert your model to second normal form you risk data redundancy and difficulty in changing data Convert first normal form tables to second normal form tables by removing columns that are not dependent on the whole primary key Third Normal Form An entity is in third normal form if it is in second normal form and all its attributes are nontransitively dependent on the primary key Transitive depen dence means that descriptor key attributes depend not only on the whole primary key but also on other descriptor key attributes that in turn depend on the whole primary key In SQL terms third normal form means that no column within a table is dependent on a descriptor column that in turn depends on the primary key To convert to third normal form remove attributes that depend on other descriptor key attributes Summary of Normalization Rules The following normal forms are discussed in this section First normal form A table is in first normal form if it contains no repeating columns Second normal form A table is in second normal form if it is in first normal form and contains only columns that are dependent on the whole primary key Third normal form A table is in third normal form if it is in second normal form and contains only c
158. 6 provides an example of using the LET statement to assign values to procedural variables through a procedure call 14 10 Creating and Using Stored Procedures Creating and Using Stored Procedures CREATE PROCEDURE address_list DEFINE p_lname p_fname p_city CHAR 15 DEFINE p_add CHAR 20 DEFINE p_state CHAR 2 DEFINE p_zip CHAR 5 LET p_fname p_lname p_add p_city p_state p_zip read_address Putnum use the returned data some way END PROCEDURE Figure 14 6 Assigning values from a procedure call with a LET statement Executing a Stored Procedure Dynamically You can prepare an EXECUTE PROCEDURE statement in conjunction with the ALLOCATE DESCRIPTOR and GET DESCRIPTOR statements in an ESQL C pro gram Parameters to the stored procedure can be passed in the same manner as the SELECT statement and may be passed at runtime or compile time For a detailed example of executing a stored procedure dynamically see Chapter 10 of the INFORMIX ESQL C Programmer s Manual For information about dynamic SQL and using a prepared SELECT statement see Chapter 5 Pro gramming with SQL Debugging a Procedure Once you successfully create and run a procedure you can encounter logical errors If logical errors are in the procedure use the TRACE statement to help find them You can trace the values of the following procedural entities e Variables e Procedure arguments e Return values SQL error
159. 7T number of rows 5 12T privilege for 11 6T 11 8T SELECT statement in 4 9T SERIAL columns 1 251S specifying values to insert 1 250S syntax 1 245S for character position form 5 29R for delimiter form 5 25R time to update indexes 10 20T use with insert cursor 1 157S VALUES clause 4 7T with a view 11 25T DECLARE 1 145S SELECT 1 253S with dbload 5 23R Inserting rows of constant data 6 11T Installation directory specifying with INFORMIXDIR 4 36R INT data type See INTEGER data type INTEGER data type changing data types 3 23R description of 3 13R 9 7T syntax 1 425S using as default value 1 195 1 89S Integrity See Data integrity Integrity See Referential integrity Integrity See Semantic integrity Intensity attributes setting INFORMIXTERM for 4 38R Interrupt key with dbexport 5 9R with dbimport 5 14R with dbload 5 21R Interrupted modifications 4 22T IS NOT keywords syntax in Condition INTERVAL data type segment 1 405S adding or subtracting from 3 30R adding or subtracting from DATETIME values 3 27R as quoted string 1 4985 description of 3 13R 9 14T display format 9 16T field delimiters 3 15R field qualifier syntax 1 485S in expression 1 4415 in INSERT 1 498S in relational expressions 2 29T multiplying or dividing values 3 31R precision and size 9 14T range of expressions 3 26R range of operations with DATE and DATETIME 3 25R syntax 1 425S 1 491S with EXTEND function 3 26R 3 28R See also L
160. 8S 6 15T locking considerations 1 152S opening 1 264S restricted statements 1 152S use in UPDATE 1 390S using 1 152S Update journal 10 33T UPDATE keyword syntax in GRANT 1 235S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 302S Update privilege column level 11 10T definition of 1 236S 11 8T with a view 1 384S 11 28T UPDATE REFERENCING clause and FOR EACH ROW section 1 121S correlation name 1 120S syntax 1 120S UPDATE statement and end of data 6 14T and transactions 1 384S applied to view 11 24T as triggered action 1 1225 as triggering statement 1 1125 1 114S 1 115S Cee Cee eS Index 47 description of 4 12T embedded 6 14T to 6 17T in trigger event 1 111S locking considerations 1 385S missing WHERE signalled 5 10T multiple assignment 4 14T number of rows 5 12T preparing 5 30T privilege for 11 6T 11 8T restrictions on columns for update 1 153S restrictions on subqueries 4 13T rolling back updates 1 385S syntax 1 383S time to update indexes 10 20T updating a column to null 1 387S updating through a view 1 384S updating with cursor 1 390S use of expressions 1 388S with Condition segment 1 404S FETCH 1 201S SET keyword 1 3865 WHERE CURRENT OF keywords 1 390S WHERE keyword 1 388S with a select for update 1 340S with an update cursor 1 152S UPDATE STATISTICS statement affect on sysdistrib 2 19R and DBUPSPACE environment variable 4 30R creating distributions 1 396S dropping data distributions
161. 9 selects the state column from the customer table and the corresponding code column from the state table SELECT DISTINCT state FROM customer WHERE customer_num BETWEEN 120 AND 125 UNION J SELECT DISTINCT code FROM state WHERE sname MATCHES a Query 3 39 Query Result 3 39 returns state code abbreviations for customer numbers 120 through 125 or for states whose sname ends in A or a state HOWDVQAPY P PP PPrPrAPrPNEN SSS 0H gt D nnvo lt AAO OPR S GROG a A Query Result 3 39 Composing Advanced SELECT Statements 3 47 Set Operations In compound queries the column names or display labels in the first SELECT statement are the ones that appear in the results Thus in Query 3 40 the col umn name state from the first SELECT statement is used instead of the column name code from the second Query 3 40 performs a union on three tables The maximum number of unions depends on the practicality of the application and any memory limitations SELECT stock_num manu_code FROM stock WHERE unit_price gt 600 00 UNION ALL SELECT stock_num manu_code FROM catalog WHERE catalog_num 10025 UNION ALL SELECT stock_num manu_code FROM items WHERE quantity 10 ORDER BY 2 Query 3 40 Query 3 40 selects items where the unit_price in the stock table is greater than 600 or the catalog_num in the catalog table is 10025 or the quantity in the items table is
162. A demon stration database is distributed with every Informix product A partial table from the demonstration database is shown in Figure 1 4 stock Table stock_num manu_code description unit_price unit unit_descr 1 HRO baseball gloves 250 00 case 10 gloves case 1 HSK baseball gloves 800 00 case 10 gloves case 1 SMT baseball gloves 450 00 case 10 gloves case 2 HRO baseball 126 00 case 24 case 3 HSK baseball bat 240 00 case 12 case 4 HSK football 960 00 case 24 case 4 HRO football 480 00 case 24 case 5 NRG tennis racquet 28 00 each each 313 ANZ swimcap 60 00 box 12 box The stock table from the demonstration database distributed with all Informix products Introducing Database Features and SQL 1 11 Important Database Terms Columns Rows A table represents all that is known about one entity one type of thing that the database describes The example table stock represents all that is known about the merchandise that is stocked by a sporting goods store Other tables in the demonstration database represent such entities as customer and orders A database can be thought of as a collection of tables To create a database is to create a set of tables The right to query or modify tables can be controlled on a table by table basis so that some users can view or modify some tables and not others Each column of a table stands for one attribute which is one characteristic feature or fact that is true of the subject of t
163. ABLE 1 175 using functions as names 1 472S using keywords as names 1 473S when qualified 1 1245 Column number 2 24T effect on triggers 1 115S Column value in triggered action 1 125S qualified vs unqualified 1 126S when unqualified 1 125S Column level privilege 1 2365 11 10T COLUMNS FOR keywords in INFO statement 1 242S Command file dbload 5 23R Command script creating database 9 26T Commit two phase 12 20T COMMIT WORK statement closes cursors 7 18T releases locks 7 8T 7 18T sets SQLCODE 6 5T syntax 1 438 Committed Read isolation level 1 3675 7 10T COMMITTED READ keywords syntax in SET ISOLATION 1 3665 Comparison condition description of 2 29T syntax and use 1 405S See also Boolean expression Compiler setting environment variable for C 4 31R setting environment variable for COBOL 4 32R 4 33R specifying storage mode for COBOL 4 33R Complex relationship 8 28T Complex condition See Condition segment Complex query example of 1 364S Composite column list multiple column restrictions 1 30S 1 31S Composite index column limit 1 655 creating with CREATE INDEX 1 635 definition of 1 655 order of columns 13 31T use 13 31T Composite key 8 23T Compound assignment 2 285 Compound query 3 43T Computer network 12 4T Concatenation operator 1 4325 Concurrency Committed Read isolation 1 367S 7 10T Cursor Stability isolation 1 3675S 7 11T database lock 7 6T deadlock 7 14T defining with SET ISOLATION 1 366S d
164. ABLE statement to add or drop a column or to change the data type of a col umn the table is copied and reconstructed If you create a clustered index or alter an index to cluster the table is sorted and rewritten See Clustered Indexes on page 10 25 In both cases the table is written on other areas of the dbspace However if other tables are in the dbspace no guarantee exists that all the new extents are adjacent Calculating Table Sizes This section discusses methods for calculating the approximate sizes of tables and indexes in disk pages As in the previous sections this information applies only to INFORMIX OnLine Dynamic Server Estimates of this kind are useful when you are planning the layout of a database on disk These calculations aim to estimate the number of disk pages that are used to hold different parts of a table If the table already exists or if you can build a demonstration table of realistic size using simulated data you do not have to make estimates You can run oncheck and obtain exact numbers You can calculate a series of values to produce the estimates You need the following values in all estimates Let the values be as follows estrows the number of rows you estimate the table has when it reaches its normal size pagesize the size of a page reported by onstat c under the head BUFFSIZE pageuse pagesize 28 the space available for data on a disk page In the calculations in this chapter
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166. ATE All rights reserved No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means graphic electronic or mechanical including photocopying recording taping or information storage and retrieval systems without permission of the publisher Published by Informix Software Inc 4100 Bohannon Drive Menlo Park CA 94025 Published by INFORMIX Press Informix Software Inc 4100 Bohannon Drive Menlo Park CA 94025 INFORMIX and C ISAM are registered trademarks of Informix Software Inc UNIX is a registered trademark licensed exclusively by the X Open Company Ltd in the United Kingdom and other countries X Open is a registered trademark of X Open Company Ltd in the United Kingdom and other countries MS and MS DOS are registered trademarks of Microsoft Corporation DOS as used herein refers to MS DOS and or PC DOS operating systems PostScript is a registered trademark of Adobe Systems Incorporated IBM is a registered trademark and DRDA is a trademark of International Business Machines Corporation Some of the products or services mentioned in this document are provided by companies other than Informix These products or services are identified by the trademark or servicemark of the appropriate company If you have a question about one of those products or services please call the company in question directly Documentation Team Robert Berry Mary Cole
167. Advanced Joins Query 3 16 uses rowid and the wildcard in the SELECT clause to retrieve every row in the manufact table and their corresponding rowids SELECT rowid FROM manufact Query 3 15 rowid manu_code manu_name lead_time 257 SMT Smith 3 258 ANZ Anza 5 259 NRG Norge 7 260 HSK Husky D 261 HRO Hero 4 262 SHM Shimara 30 263 KAR Karsten 21 264 NKL Nikolus 8 265 PRC ProCycle 9 Query Result 3 15 You also can use rowid when you select a specific column as shown in Query 3 16 SELECT rowid manu_code FROM manufact Query 3 16 rowid manu_code 258 ANZ 261 HRO 260 HSK 263 KAR 264 NKL 259 NRG 265 PRC 262 SHM 257 SMT Query Result 3 16 3 18 Composing Advanced SELECT Statements Creating Advanced Joins You also can use the rowid in the WHERE clause to retrieve rows based on their internal record number This method is handy when no other unique column exists in a table Query 3 17 uses the rowid from Query 3 16 SELECT FROM manufact WHERE rowid 263 Query 3 17 Query 3 17 returns the row shown in Query Result 3 17 manu_code manu_name lead_time KAR Karsten 21 Query Result 3 17 Using the USER Function To obtain additional information about a table you can combine the rowid with the USER function Query 3 18 assigns the label username to the USER expression column and returns this information about the cust_calls table SELECT USER username rowid FROM
168. Cost of Sequential Access 17 The Cost of Nonsequential Access 18 The Cost of Rowid Access 18 The Cost of Indexed Access 18 The Cost of Small Tables 19 The Cost of NLS Functionality 19 The Cost of Network Access 20 The Importance of Table Order 22 A Join Without Filters 22 A Join with Column Filters 23 Using Indexes 26 The Sort Merge Join Technique 27 Making Queries Faster 27 Preparing a Test Environment 28 Studying the Data Model 28 Studying the Query Plan 29 Examining the Indexes 29 Replacing Autoindexes with Indexes 29 Creating Data Distributions on Filtered Columns 29 Using Composite Indexes 31 Using oncheck on Suspect Indexes 31 Dropping and Rebuilding Indexes After Updates 31 Refining the Column Filters 31 Avoiding Correlated Subqueries 32 Avoiding Difficult Regular Expressions 32 Avoiding Noninitial Substrings 33 Rethinking the Query 33 Rewriting Joins Through Views 33 Avoiding or Simplifying Sorts 33 Eliminating Sequential Access to Large Tables 34 Using Unions to Avoid Sequential Access 35 Reviewing the Optimization Level 36 Using a Temporary Table to Speed Queries 36 Using a Temporary Table to Avoid Multiple Sorts 36 Substituting Sorting for Nonsequential Access 37 Summary 41 13 2 Optimizing Your Queries Chapter Overview How much time should a query take How many disk operations should the computer perform while executing a query For many queries it does not matter as long as the computer finds the information
169. DURE FROM 14 5T syntax 1 68S use of dbschema 5 34R using 14 5T CREATE SCHEMA statement defining a trigger 1 1115 syntax 1 778 with CREATE sequences 1 785 with GRANT 1 788 CREATE SYNONYM statement ANSI compliant naming 1 80S chaining synonyms 1 83S synonym for a table 1 80S synonym for a view 1 80S syntax 1 80S use of dbschema 5 34R with CREATE SCHEMA 1 77S CREATE TABLE use of dbschema 5 34R CREATE TABLE statement and COLLCHAR environment variable 4 46R and NCHAR column 1 19R and NVARCHAR column 1 19R cascading deletes 1 975 CHECK clause 1 985 creating temporary table 1 100S DEFAULT clause 1 885 defining constraints at column level 1 915 at table level 1 925 description of 9 24T EXTENT SIZE clause 10 8T in command script 9 26T IN dbspace clause 1 105S locating BLOB column 10 18T LOCK MODE clause 1 108S naming conventions 1 845 NEXT SIZE clause 10 8T ON DELETE CASCADE keyword 1 945 REFERENCES clause 1 945 rules for primary keys 1 94S rules for referential constraints 1 945 rules for unique constraints 1 94S sets initial SERIAL value 9 8T setting columns NOT NULL 1 205 1 905 specifying extent size 1 107S specifying table columns 1 875 storing database tables 1 105S syntax 1 845 with BLOB data types 1 915 with CREATE SCHEMA 1 77S CREATE TRIGGER statement in ESQL C 1 111S in ESQL COBOL 1 111S privilege to use 1 111S purpose 1 110S syntax 1 110S triggered action clause 1 121S use 1 1115 CREATE VIEW state
170. Database Server integer 10 K 0D 0 Success 100 No more data not found negative Error code L array of 6 integers SQLERRD first Following successful prepare of a SELECT UPDATE INSERT or DELETE statement or after a select cursor is opened this field contains the estimated number of affected rows It is not used in INFORMIX ESQL Ada second When SQLCODE contains an error code this field contains either zero or an additional error code called the ISAM error code that explains the cause of the main error After a failed CONNECT or DATABASE statement this field contains the ISAM operating system or network specific protocol error code If an application connects to an INFORMIX Gateway with DRDA this field contains the application server error code In this case sqlca sqlcode is 29000 Following a successful insert operation of a single row this field contains the value of a generated serial number for that row third Following a successful multirow insert update or delete operation this field contains the number of processed rows Following a multirow insert update or delete operation that ends with an error this field contains the number of rows successfully processed before the error was detected fourth Following successful prepare of a SELECT UPDATE INSERT or DELETE statement or after a select cursor has been opened this field contains the estimated weighted sum of disk accesses and t
171. Dynamic Server Administrator s Guide Database access is regulated by the privileges that the database owner grants to you The privileges that let you query data are often granted automatically but the ability to modify data is regulated by specific Insert Delete and Update privileges that are granted on a table by table basis If data integrity constraints are imposed on the database your ability to modify data is restricted by those constraints Your database and table level privileges along with any data constraints control how and when you can modify data You can delete one or more rows from a table with the DELETE statement Its WHERE clause selects the rows use a SELECT statement with the same clause to preview the deletes Rows are added to a table with the INSERT statement You can insert a single row containing specified column values or you can insert a block of rows generated by a SELECT statement You use the UPDATE statement to modify the contents of existing rows You specify the new contents with expressions that can include subqueries so that you can use data based on other tables or the updated table itself The statement has two forms in the first form you specify new values column by column you use the other form when the new values are generated as a set from a SELECT statement or a record variable Modifying Data 4 29 Summary 4 30 Modifying Data You use the REFERENCES clause of the CREATE TABLE a
172. E data type as opposed to TEXT or CHAR n is that it accepts any data Its disadvantages are the same as those of the TEXT data type Changing the Data Type You can use the ALTER TABLE statement to change the data type assigned to a column after the table is built Although this is sometimes necessary you should avoid doing it for the following reasons e To change a data type the database server must copy and rebuild the table For large tables that can take a lot of time and disk space Some data type changes can cause a loss of information For example when you change a column from a longer to a shorter character type long values are truncated when you change to a less precise numeric type low order digits are truncated e Existing programs forms reports and stored queries also might have to be changed Default Values A default value is the value inserted into a column when an explicit value is not specified in an INSERT statement A default value can be a literal charac ter string defined by you or one of the following SQL null constant expressions e USER CURRENT Implementing Your Data Model 9 19 Creating the Database TODAY DBSERVERNAME Not all columns need default values but as you work with your data model you may discover instances where the use of a default value saves data entry time or prevents data entry error For example the telephone directory model has a State column While loo
173. ECT customer_num DATE call_dtime DATE res_dtime FROM cust_calls called resolved 2 62 WHERE call_dtime gt DATE 1 1 93 Query 2 63 customer_num called resolved 106 06 12 1993 06 12 1993 110 07 07 1993 07 07 1993 119 07 01 1993 07 02 1993 121 07 10 1993 07 10 1993 127 07 31 1993 Query Result 2 63 Composing Simple SELECT Statements Single Table SELECT Statements Other Functions and Keywords You also can use the LENGTH USER CURRENT and TODAY functions anywhere in an SQL expression that you would use a constant In addition with INFORMIX OnLine Dynamic Server you can include the DBSERVER NAME keyword in a SELECT statement to display the name of the database server where the current database resides You can use these functions and keywords to select an expression that consists entirely of constant values or an expression that includes column data In the first instance the result is the same for all rows of output In addition you can use the HEX function to return the hexadecimal encoding of an expression the ROUND function to return the rounded value of an expression and the TRUNC function to return the truncated value of an expression In Query 2 64 the LENGTH function calculates the number of bytes in the combined fname and Iname columns for each row where the length of company is greater than 15 SELECT customer_num LENGTH fname LENGTH lname namelength FROM customer WHERE LEN
174. GROUP BY clause 1 334S 3 4T HAVING clause 1 336S 3 9T IN condition 1 327S in FOR EACH ROW section 1 1175 in modifiable view 11 24T INTO clause with ESQL 1 318S INTO TEMP clause 1 341S 2 83T IS NULL condition 1 327S join 2 71T to 2 79T joining tables in WHERE clause 1 331S LIKE or MATCHES condition 1 328S multiple table 2 69T natural join 2 75T null values in the ORDER BY clause 1 3395 ORDER BY clause 1 3375 2 13T ORDER BY clause and NLS 1 15R outer join 3 21T to 3 31T privilege for 11 6T 11 8T relational operator condition 1 326S restrictions with INTO clause 1 276S rowid 3 16T 3 21T ROWID keyword 1 435S SELECT clause 1 3125 2 12T to 2 28T select numbers 1 339S selecting a substring 2 27T selecting expressions 2 46T selection list 2 12T self join 3 11T single table 2 11T singleton 1 318S 2 29T subquery 3 32T to 3 42T subquery with WHERE keyword 1 326S syntax 1 310S UNION operator 1 344S 3 43T use of expressions 1 313S using for join 2 8T for projection 2 7T for selection 2 5T WHERE clause and NLS 1 15R with Condition segment 1 404S DECLARE 1 145S FOREACH 2 208 INSERT 1 253S INTO keyword 1 198S LET 2 295 writing rows retrieved to an ASCII file 1 378S Selection described 2 5T Self join assigning column names with INTO TEMP 3 12T description of 1 333S 3 11T See also Join Self referencing query 3 11T 4 22T Self referencing query See also Self join Semantic integrity 4 18T 9 3T Sequential ac
175. GTH company gt 15 Query 2 64 customer_num namelength L01 LO5 LO7 L12 L15 118 119 L20 22 124 L25 126 L27 128 BHO RNG HN OOT Ha a a e Query Result 2 64 Composing Simple SELECT Statements 2 63 Single Table SELECT Statements Although it might not be useful when you work with the DB Access or INFORMIX SQL Interactive Editor the LENGTH function can be important to determine the string length for programs and reports LENGTH returns the clipped length of a CHARACTER or VARCHAR string and the full number of bytes in a TEXT or BYTE string The USER function can be handy when you want to define a restricted view of a table that contains only your rows For information on creating views see Chapter 11 Granting and Limiting Access to Your Database in this manual and the GRANT and CREATE VIEW statements in Chapter 1 of the Informix Guide to SQL Syntax Query 2 65a specifies the USER function and the cust_calls table SELECT USER from cust_calls Query 2 65a Query 2 65b returns the user name login account name of the user who executes the query It is repeated once for each row in the table SELECT FROM cust_calls WHERE user_id USER Query 2 65b If the user name of the current user is richc Query 2 65b retrieves only those rows in the cust_calls table that are owned by that user customer_num 10 call_dtime 993 07 07 10 24 user_id riche call_code L call
176. IME data type 1 428S in INTERVAL data type 1 485S use as DATETIME field qualifier 3 8R 1 488S as INTERVAL field qualifier 3 14R 1 491S Hyphen as delimiter in DATETIME 3 9R as delimiter in INTERVAL 3 15R I Icon explanation of Intro 65 IDATA field SET DESCRIPTOR statement 1 357S with X Open programs 1 213S Identifier segment column names 1 4765 column naming allowable characters 1 469S cursor name 1 482S cursor names 1 479S database objects that use 1 469S stored procedures 1 479S syntax 1 469S table names 1 475S 1 477S used in column naming 1 885 using keywords as column names 1 473S variable name 1 4815 IF statement branching 14 22T syntax 2 245 syntax and use 2 245 with null values 2 255 ILENGTH field SET DESCRIPTOR statement 1 357S with X Open programs 1 213S IMMEDIATE keyword in the SET CONSTRAINTS statement 1 349S Implicit connection defined 1 465 with DISCONNECT 1 168S Implicit temporary table 1 100S IN keyword locating BLOB column 10 18T syntax in CREATE AUDIT 1 555 in CREATE DATABASE 1 575 in CREATE TABLE 1 105S in LOCK TABLE 1 260S use in Condition segment 1 408S in Condition subquery 1 414S in CREATE DATABASE 10 5T in CREATE TABLE 10 6T 10 8T with WHERE keyword 1 327S IN keyword used to test for equality in WHERE clause 2 29T IN relational operator 3 33T Index adding for performance 10 21T 13 34T allowable characters in index name 1 469S building with NLS 1 20R clustered
177. INFORMIX OnLine Dynamic Server uses assumes that access to a row over the network takes longer than access to a row in a local database This estimate includes the cost of retrieving the row from disk and transmitting it across the network The optimizer has no way to account for varying network loads so it is too pessimistic at times and too optimistic at others Optimizing Your Queries 13 21 Time Costs of a Query The Importance of Table Order The order in which tables are examined has an enormous effect on the speed of a join operation This concept can be clarified with some examples that show how the database server works A Join Without Filters The following SELECT statement calls for a three way join SELECT C customer_num O order_num SUM I total_price FROM customer C orders O items I WHERE C customer_num O customer_num AND O order_num I order_num GROUP BY C customer_num O order_num For the moment imagine that indexes were never invented Without indexes the database server has no choice but to perform this operation using a sim ple nested loop One of two practical query plans is displayed in Figure 13 2 which is expressed in a programming pseudocode A query plan states the order in which the database server examines tables and the methods by which it accesses the tables for each row in the customer table do read the row into C for each row in the orders table do read the row into O if O custom
178. Informix Guide to SOL Tutorial Informix Guide to SQL Tutorial Version 6 0 March 1994 Part No 000 7598 ii THE INFORMIX SOFTWARE AND USER MANUAL ARE PROVIDED AS IS WITHOUT WARRANTY OF ANY KIND EITHER EXPRESSED OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE INFORMIX SOFTWARE AND USER MANUAL IS WITH YOU SHOULD THE INFORMIX SOFTWARE AND USER MANUAL PROVE DEFECTIVE YOU AND NOT INFORMIX OR ANY AUTHORIZED REPRESENTATIVE OF INFORMIX ASSUME THE ENTIRE COST OF ALL NECESSARY SERVICING REPAIR OR CORRECTION IN NO EVENT WILL INFORMIX BE LIABLE TO YOU FOR ANY DAMAGES INCLUDING ANY LOST PROFITS LOST SAVINGS OR OTHER INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF OR INABILITY TO USE SUCH INFORMIX SOFTWARE OR USER MANUAL EVEN IF INFORMIX OR AN AUTHORIZED REPRESENTATIVE OF INFORMIX HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES OR FOR ANY CLAIM BY ANY OTHER PARTY IN ADDITION INFORMIX SHALL NOT BE LIABLE FOR ANY CLAIM ARISING OUT OF THE USE OF OR INABILITY TO USE SUCH INFORMIX SOFTWARE OR USER MANUAL BASED UPON STRICT LIABILITY OR INFORMIX S NEGLIGENCE SOME STATES DO NOT ALLOW THE EXCLUSION OF IMPLIED WARRANTIES SO THE ABOVE EXCLUSION MAY NOT APPLY TO YOU IN WHOLE OR IN PART THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS AND YOU MAY ALSO HAVE OTHER RIGHTS WHICH VARY FROM STATE TO ST
179. Informix documents that complement this manual 4 Introduction A companion volume to the Tutorial the Informix Guide to SQL Reference provides reference information on the types of Informix databases you can create the data types supported in Informix products system catalog tables associated with the database environment variables and the SQL utilities This guide also provides a detailed description of the stores6 demonstration database and contains a glossary An additional companion volume to the Tutorial the Informix Guide to SQL Syntax provides a detailed description for all of the SQL statements supported by Informix products This guide also provides a detailed description of stored procedure language SPL statements The SQL Quick Syntax Guide contains syntax diagrams for all statements and segments described in this manual You or whoever installs your Informix products should refer to the UNIX Products Installation Guide for your particular release to ensure that your Informix product is properly set up before you begin to work with it A matrix depicting possible client server configurations is included in the Installation Guide Depending on the database server you are using you or your system administrator need either the INFORMIX SE Administrator s Guide or the INFORMIX OnLine Dynamic Server Administrator s Guide and INFORMIX OnLine Dynamic Server Archive and Backup Guide The DB Access User Manual describ
180. Informix extension checking specifying with DBANSIWARN 4 15R INFORMIX 4GL 12 5T detecting null value 5 16T example of dynamic SQL 11 13T indicator variable not used 5 16T program variable 5 5T STATUS variable 5 11T terminates on errors 5 36T 6 14T timing operations in 13 6T using SQLCODE with 5 11T WHENEVER ERROR statement 5 36T INFORMIXC environment variable 4 31R INFORMIXCOB environment variable 4 32R INFORMIXCOBDIR environment variable 4 32R INFORMIXCOBSTORE environment variable 4 33R INFORMIXCOBTYPE environment variable 4 33R INFORMIXCONRETRY environment variable 4 34R INFORMIXCONTIME environment variable 4 34R INFORMIXDIR environment variable 4 36R 12 14T INFORMIX OnLine disk access by 13 17T INFORMIX OnLine Dynamic Server allows views on external tables 11 23T and triggering statement 1 112S archiving 4 26T characteristics of 1 10T creating demonstration database Intro 10R Intro 13S disk page size 13 16T disk storage methods 10 3T to 10 12T is NLS ready 1 15R optimizer input with 13 9T signalled in SQLAWARN 5 12T when tables are locked 7 7T INFORMIX OnLine Optical 12 6T list of statements 1 7S INFORMIX SE characteristics of 1 10T creating database 9 23T creating demonstration database Intro 10R Intro 13S is NLS ready 1 15R INFORMIXSERVER environment variable 4 36R 1 46S 12 14T INFORMIXSHMBASE environment variable 4 37R INFORMIX SQL Index 23 24 Index creating d
181. MONTH WEEKDAY YEAR and DATE in either the SELECT clause or the WHERE clause of a query These func tions return a value that corresponds to the expressions or arguments that you use to call the function You also can use the CURRENT function to return a value with the current date and time or the EXTEND function to adjust the precision of a DATE or DATETIME value 2 56 Composing Simple SELECT Statements Single Table SELECT Statements Using DAY and CURRENT Query 2 53 returns the day of the month for the call_dtime and res_dtime columns in two expression columns as shown in Query Result 2 53 SELECT customer_num DAY call_dtime DAY res_dtime FROM cust_calls Query 2 53 customer_num expression expression 106 I2 12 110 7 7 119 I 2 121 10 10 127 31 116 28 28 116 21 27 Query Result 2 53 Query 2 54 uses the DAY and CURRENT functions to compare column values to the current day of the month It selects only those rows where the value is earlier than the current day SELECT customer_num DAY call_dtime DAY res_dtime FROM cust_calls WHERE DAY call_dtime lt DAY CURRENT Query 2 54 customer_num expression expression 106 12 12 110 g 7 119 121 10 10 Query Result 2 54 Composing Simple SELECT Statements 2 57 Single Table SELECT Statements Query 2 55 shows another use of the CURRENT function selecting rows where the day is earlier than the current one SELECT custo
182. N END block BEGIN DEFINE c INT ON EXCEPTION IN 206 table does not exist 217 column does not exist SET err_num IF err_num 206 THEN REATE TABLE t c INT iNSERT INTO t VALUES 10 continue after the insert statement Q LTER TABLE t ADD d INT ET c SELECT d FROM t continue after the select statement END IF END EXCEPTION WITH RESUME E E INSERT INTO t VALUES 10 will fail if t does not exist LET c SELECT d FROM t will fail if d does not exist END An ON EXCEPTION statement within a BEGIN END block When an error occurs the SPL interpreter searches for the innermost ON EXCEPTION declaration that traps the error Note that the first action after trapping the error is to reset the error When execution of the error action code is complete and if the ON EXCEPTION declaration that was raised included the WITH RESUME keywords execution resumes automatically with the statement following the statement that generated the error If the ON EXCEPTION declaration did not include the WITH RESUME keywords execution exits the current block completely 14 28 Creating and Using Stored Procedures Exception Handling Scope of Control of an ON EXCEPTION Statement An ON EXCEPTION statement is valid for the statement block that follows the ON EXCEPTION statement all of the statement blocks nested within that fol lowing statement block an
183. NG INT DEFINE result INT IF strl gt str2 THEN result 1 ELIF str2 gt stri THEN result 1 ELSE result 0 END IF RETURN result END PROCEDURE str_compare Using an IF statement Three methods exist of looping in SPL accomplished with one of the following statements FOR initiates a controlled loop Termination is guaranteed FOREACH allows you to select and manipulate more than one row from the database It declares and opens a cursor implicitly WHILE initiates a loop Termination is not guaranteed Four ways exist to leave a loop which can accomplished with one of the following statements CONTINUE skips the remaining statements in the present identified loop and starts the next iteration of that loop EXIT exits the present identified loop Execution resumes at the first statement after the loop RETURN exits the procedure If a return value is specified that value is returned upon exit RAISE EXCEPTION exits the loop if the exception is not trapped caught in the body of the loop See Chapter 2 of the Informix Guide to SQL Syntax for more information concerning the syntax and use of these statements Creating and Using Stored Procedures 14 23 Program Flow Control Function Handling You can call procedures as well as run operating system commands from within a procedure Calling Procedures Within a Procedure Figure 14 11 Use a CALL statement or the SQL statement E
184. ON table_grant priv_to_grant table_name user_id DEFINE priv_to_grant char 100 table name char 20 user_id char 20 grant_stmt char 200 LET grant_stmt GRANT priv_to_grant ON table_name TO user_id WHENEVER ERROR CONTINUE PREPARE the_grant FROM grant_stmt IF status 0 THEN EXECUTE the_grant END IF IF status lt gt 0 THEN DISPLAY Sorry got error status attempting DISPLAY grant_stmt END IF FREE the_grant WHENEVER ERROR STOP END FUNCTION i Il A 4GL function that builds prepares and executes a GRANT statement The opening statement shown in the following example defines the name of the function and the names of its three parameters FUNCTION table_grant priv_to_grant table_name user_id Programming with SQL 5 35 Embedding Data Definition Statements The DEFINE statement shown in the following example defines the parameters and one additional variable local to the function All four are character strings of various lengths DEFINE priv_to_grant char 100 table_name char 20 user_id char 20 grant_stmt char 200 The variable grant_stmt holds the assembled GRANT statement which is created by concatenating the parameters and some constants This is shown in the following example LET grant_stmt GRANT priv_to_grant ON table_name TO user_id In INFORMIX 4GL the comma is used to concatenate string
185. P environment variable 4 40R PSORT_NPROCS environment variable 4 41R sort merge join 13 27T time costs of 13 15T when there are multiple active NLS locales 1 20R with NLS activated 1 15R 2 25T with ORDER BY 2 14T See also ORDER BY keywords Space as delimiter in DATETIME 3 9R as delimiter in INTERVAL 3 15R Specifying ANSI compliance 1 11R SPL flow control statements 14 22T program variable 5 5T relation to SQL 14 3T See also Stored procedure SQL ANSI standard 1 15T cursor 5 19T description of 1 14T error handling 5 16T history 1 14T in NLS ready products 1 22R Informix SQL and ANSI SQL 1 15T interactive use 1 17T optimizing See Optimizer standardization 1 14T statement types 1 55 SQL Communications Area GSQLCA altered by end of transaction 6 5T description of 5 8T effect of setting DBANSIWARN 4 15R inserting rows 6 11T result after CLOSE 1 398 result after DATABASE 1 140S result after DESCRIBE 1 163S result after FETCH 1 202S result after FLUSH 1 204S result after OPEN 1 264S 1 265S result after PUT 1 290S result after SELECT 1 321S returning NLS error messages to 1 19R See also SQLAWARN SQLCODE and SQLERRD SQL DESCRIPTOR clause See DESCRIBE statement SQL Descriptor See SQL Communications Area SQLCA SQL statements FILE 5 23R INSERT 5 23R SQLAWARN array description of 5 12T syntax of naming 5 11T with PREPARE 5 30T sqlca record and EXECUTE statement 1 186S SQLCA See SQL Comm
186. PAGE keyword use in ALTER TABLE 1 335 use in CREATE TABLE 1 108S Page lock 7 8T Page definition of 10 4T Parameter BYTE or TEXT in SPL 2 135 in CALL statement 2 45 to a stored procedure 14 25T Parameterizing a statement with SQL identifiers 1 279S Parent child relationship 1 215 1 945 Parts explosion 5 26T PATH environment variable 4 54R 12 14T Pathname including in SQLEXEC 4 42R specifying with DBPATH 4 21R specifying with PATH 4 54R Percent sign wildcard in Condition segment 1 410S PERFORM keyword in the WHENEVER statement 1 398S Performance adding indexes 13 34T assigning table to dedicated disk 10 6T bottleneck tables 10 35T buffered log 9 22T clustered index 10 25T depends on concurrency 7 3T disk access 13 14T 13 17T 13 34T disk access by rowid 13 18T disk arm motion 10 8T disk latency 13 17T dropping indexes to speed modifications 10 24T duplicate keys slow modifications 10 22T effect of BLOB location 10 18T correlated subquery 13 32T filter expression 13 23T 13 32T 13 33T index damage 13 31T indexes 10 21T to 10 22T 13 26T regular expressions 13 32T table size 13 19T 13 34T updates 13 31T filter selectivity 13 30T hot spots finding 13 7T improved by specifying optimization level 13 36T improved with temporary table 13 36T improving 13 27T increasing with stored procedures 14 4T index time during modification 10 20T interleaved dbspaces 10 10T journal updates 10 33T measurement 13 6T
187. Pages 4 Dbspaces and Blobspaces 4 Disk Mirroring 5 Databases 5 Tables and Spaces 6 Exploiting Mirroring 6 Sharing Temporary Space 6 Assigning Dedicated Hardware 6 Reducing Contention Between Programs Using the Same Table 7 Tblspaces 7 Extents 8 Choosing Extent Sizes 8 Upper Limit on Extents 10 Reorganizing dbspaces and Tables 10 Calculating Table Sizes 12 Estimating Fixed Length Rows 13 Estimating Variable Length Rows 14 Estimating Index Pages 16 Estimating Blobpages 17 Locating Blob Data 18 Managing Indexes 19 Space Costs of Indexes 20 Time Costs of Indexes 20 Choosing Indexes 21 Join Columns 21 Selective Filter Columns in Large Tables 22 Order By and Group By Columns 22 Duplicate Keys Slow Index Modifications 22 Dropping Indexes 24 Clustered Indexes 25 Denormalizing 26 Shorter Rows for Faster Queries 26 Expelling Long Strings 26 Using VARCHAR Strings 26 Changing Long Strings to TEXT 27 Building a Symbol Table of Repeated Strings 27 Moving Strings toa Companion Table 28 Splitting Wide Tables 28 Division by Bulk 28 Division by Frequency of Use 28 Division by Frequency of Update 29 Costs of Companion Tables 29 Splitting Tall Tables 29 Redundant and Derived Data 30 Adding Derived Data 30 Adding Redundant Data 31 Maximizing Concurrency 32 Easing Contention 32 Rescheduling Modifications 33 Using an Update Journal 33 Isolating and Dispersing Updates 35 Splitting Tables to Isolate VolatileColumns 35 Dispersing Bottle
188. Programs 6 17 Summary 6 18 Modifying Data Through SQL Programs Programming for a Multiuser Environment Chapter Overview 3 Concurrency and Performance 3 Locking and Integrity 3 Locking and Performance 3 Concurrency Issues 4 How Locks Work 5 Kinds of Locks 6 Lock Scope 6 Database Locks 6 Table Locks 7 Page Row and Key Locks 8 The Duration of aLock 8 Locks While Modifying 9 Setting the Isolation Level 9 Dirty Read Isolation 10 Committed Read Isolation 10 Cursor Stability Isolation 11 Repeatable Read Isolation 12 Setting the Lock Mode 13 Waiting for Locks 13 Not Waiting for Locks 13 Waiting a Limited Time 14 Handling a Deadlock 14 Handling External Deadlock 14 Simple Concurrency 15 Locking with Other Database Servers 15 Isolation While Reading 16 Locking Updated Rows 17 Hold Cursors 17 Summary 19 7 2 Programming for a Multiuser Environment Chapter Overview If your database is contained in a single user workstation and is not connected on a network to other machines your programs can modify data freely But in all other cases you must allow for the possibility that while your program is modifying data another program is reading or modifying the same data This is concurrency two or more independent uses of the same data at the same time This chapter addresses concurrency locking and isolation levels Concurrency and Performance Concurrency is crucial to good performance in a multiprogrammi
189. QLCODE and SQLERRD When your program uses a cursor to select rows it can test SQLCODE for 100 the end of data return code This is set to indicate that no rows or no more rows satisfy the query conditions The end of data return code is set in SQLCODE only following SELECT statements it is not used following DELETE INSERT or UPDATE statements A query that finds no data is not a success However an UPDATE or DELETE statement that happens to update or delete no rows is still considered a success it updated or deleted the set of rows that its WHERE clause said it should however the set was empty In the same way the INSERT statement does not set the end of data return code even when the source of the inserted rows is a SELECT statement and it selected no rows The INSERT statement is a success because it inserted as many rows as it was asked to do that is zero To find out how many rows are inserted updated or deleted a program can test the third element of SOQLERRD The count of rows is there regardless of the value zero or negative in SQLCODE 6 14 Modifying Data Through SQL Programs Using UPDATE Using an Update Cursor An update cursor permits you to delete or update the current row that is the most recently fetched row The following example in INFORMIX ESQL COBOL show the declaration of an update cursor EXEC SQL DECLARE names CURSOR FOR SELECT fname lname company FROM customer FOR UPDATE END E
190. R m r data type or NVARCHAR m r when NLS has been enabled is designed to save disk space when storing such data A column defined as VARCHAR m r or NVARCHAR m r is used just like one defined as CHAR n When you define a VARCHAR m r or NVARCHAR m r column you specify mas the maximum length of a data item Only the actual contents of each item are stored on disk with a 1 byte length field The limit on m is 255 that is a VARCHAR m r or NVARCHAR m r value can store as many as 255 characters If the column is indexed the limit on m is 254 Implementing Your Data Model 9 15 Defining the Domains Forcing the Format of a DATETIME or INTERVAL Value The database server always displays the components of an INTERVAL or DATETIME value in the order year month day hour minute second fraction It does not refer to the date format defined to the operating system as it does when formatting a DATE You can write a SELECT statement that displays the date part of a DATETIME value in the system defined format The trick is to isolate the component fields using the EXTEND function and pass them through the MDY function which converts them to a DATE The following code is a partial example SELECT MDY EXTEND DATE_RECEIVED MONTH TO MONTH EXTEND DATE_RECEIVED DAY TO DAY EXTEND DATE_RECEIVED YEAR TO YEAR FROM RECEIPTS When you are designing a report using INFORMIX 4GL or INFORMIX SQL you have the gre
191. RN next_free 1 END FUNCTION A breadth first algorithm to generate a parts explosion Technically speaking each row of the contains table is the head node of a directed acyclic graph or tree The function in Figure 5 6 performs a breadth first search of the tree whose root is the part nu The function uses a cursor named part_scan to mber passed as its parameter return all the rows with a par ticular value in the parent column This is very easy to implement using the INFORMIX 4GL statement FOREACH which opens a cursor iterates once for each row in the selection set and closes the cursor Programming with SQL 5 27 Dynamic SQL This is the heart of the parts explosion problem but it is not a complete solution For example the program in Figure 5 6 does not allow for compo nents that appear at more than one level in the tree Furthermore a practical contains table would also have a column count giving the count of child parts used in each parent A program that returns a total count of each component part is much more complicated The iterative approach described earlier is not the only way to approach the parts explosion problem If the number of generations has a fixed limit you can solve the problem with a single SELECT statement using nested outer self joins If there can be up to four generations of parts contained within one top level part the following SELECT statement returns all of them SELECT a parent a
192. RWBE DN 1018 1002 1004 1014 1019 1021 1007 Ok He No BN WI Query Result 3 3 number SUM total_price price 84 99 143 232 250 438 448 450 450 1131 1200 1416 1440 1499 1614 1696 00 00 00 97 00 price As stated in Chapter 2 Composing Simple SELECT Statements you can use an integer in an ORDER BY clause to indicate the position of a column in the select list You also can use an integer in a GROUP BY clause to indicate the position of column names or display labels in the group list Composing Advanced SELECT Statements 3 7 Using the GROUP BY and HAVING Clauses Query 3 3 returns the same rows as Query 3 4 as shown in Query Result 3 3 SELECT order_num COUNT number SUM total_price price FROM items GROUP BY 1 ORDER BY 3 Query 3 4 When you build a query remember that all nonaggregate columns that are in the select list in the SELECT clause must also be included in the group list in the GROUP BY clause The reason for this is that a SELECT with GROUP BY must return only one row per group Columns that are listed after GROUP BY are certain to reflect only one distinct value within a group and that value can be returned However a column not listed after GROUP BY might contain different values in the rows that are contained in a group As shown in Query 3 5 you can use the GROUP BY clause in a SELECT statement that joins tables SELECT
193. Restricting access using file system 11 4T Result of triggering statement 1 123S RETURN statement exiting a loop 14 23T returning insufficient values 2 385 returning null values 2 385 syntax 2 388 REVOKE statement column specific privileges 1 303S database level privileges 1 303S granting privileges 11 5T to 11 15T in embedded SQL 5 34T to 5 37T privileges needed 1 301S syntax 1 300S table level privileges 1 301S with a view 11 29T ROLLBACK WORK statement cancels a transaction 4 25T closes cursors 7 18T releases locks 7 8T 7 18T sets SOQLCODE 6 5T syntax 1 306S use with WHENEVER 1 368 1 425 1 3075 with DROP DATABASE 1 173S with DROP INDEX statement 1 175S with DROP PROCEDURE statement 1 176S with DROP SYNONYM statement 1 177S with DROP TABLE statement 1 179S with DROP TRIGGER statement 1 181S with DROP VIEW statement 1 183S ROLLFORWARD DATABASE statement applies log to restored database 4 26T exclusive locking 1 308S syntax 1 308S Root dbspace definition of 10 5T ROOT function syntax in expression 1 444S use in expression 1 446S ROUND function syntax in expression 1 444S use in expression 1 446S Row cost of reading from disk 13 16T defined 2 5T defining 8 20T deleting 1 1595 4 4T description of 1 12T engine response to locked row 1 370S in relational model 1 12T 8 20T inserting 4 6T inserting through a view 1 246S inserting with a cursor 1 248S multi row queries with FETCH 1 195S order guaranteeing i
194. Rows that do not satisfy the join conditions are discarded In an outer join the result contains the combinations of rows from the tables that satisfy the join conditions Rows from the dominant table that would other wise be discarded are preserved even though no matching row was found in the sub servient table The dominant table rows that do not have a matching subservient table row receive a row of nulls before the selected columns are projected An outer join applies conditions to the subservient table while sequentially applying the join conditions to the rows of the dominant table The condi tions are expressed in a WHERE clause An outer join must have a SELECT clause a FROM clause and a WHERE clause You transform a simple join into an outer join by inserting the key word OUTER directly before the name of the subservient tables in the FROM clause As shown later in this section you can include the OUTER keyword more than once in your query Before you use outer joins heavily you should determine whether one or more simple joins can work You often can get by with a simple join when you do not need supplemental information from other tables The examples in this section use table aliases for brevity Table aliases are discussed in the preceding chapter Simple Join Query 3 21 is an example of the type of simple join on the customer and cust_calls tables shown in Chapter 2 Composing Simple SELECT State ments
195. SQL 1 13 Structured Query Language Structured Query Language Most computer software has not yet reached a point where you can literally ask a database what orders have been placed by customers in New Jersey with ship dates in the second quarter You must still phrase questions in a restricted syntax that the software can easily parse You can pose the same question to the demonstration database in the following terms SELECT FROM customer orders WHERE customer customer_num orders customer_num AND customer state NJ AND orders ship_date BETWEEN DATE 7 1 93 AND DATE 7 30 93 This question is a sample of Structured Query Language SQL It is the language that you use to direct all operations on the database SQL is com posed of statements each of which begins with one or two keywords that specify a function SQL includes about 73 statements from ALLOCATE DESCRIPTOR to WHENEVER All the SQL statements are specified in detail in the Informix Guide to SQL Syntax Most of the statements are used infrequently when setting up or tuning a database People generally use three or four statements to query or update databases One statement SELECT is in almost constant use It is the only statement that you can use to retrieve data from the database It is also the most complicated statement and the next two chapters of this book are devoted to exploring its many uses Standard SOL SQL and the relational mo
196. STICS 1 3945 Optimizing a query 1 360S a server 1 3745 across a network 1 374S techniques 13 3T Optional entity in relationship 8 9T OR keyword syntax in Condition segment 1 404S Index 31 use in Condition segment 1 417S OR logical operator 2 36T OR relational operator 2 33T ORDER BY keywords and NLS 2 25T ascending order 1 338S 2 14T DESC keyword 2 15T 2 25T descending order 1 338S display label with 2 52T indexes for 13 10T 13 34T multiple columns 2 15T relation to GROUP BY 3 7T restrictions in INSERT 1 253S 4 10T restrictions in view 11 22T restrictions with FOR UPDATE 6 8T select columns by number 1 339S 2 24T sorting rows 2 13T 13 12T syntax in SELECT 1 310S use in SELECT 1 337S with UNION operator 1 344S Order of execution of action statements 1 122S orders table in stores6 database columns in A 3R Outer join forming 1 324S OUTER keyword with FROM keyword in SELECT 1 323S Output from TRACE command 15 14T OUTPUT statement syntax and use 1 271S Owner in ALTER TABLE 1 16S in CREATE SYNONYM 1 808 in dbschema 5 35R in Index Name segment 1 419S 1 484S 1 495S 1 505S in RENAME COLUMN 1 294S in RENAME TABLE 1 296S in Table Name segment 1 4698S 1 507S in View Name segment 1 510S of view in CREATE VIEW 1 5115S Owner privileged procedure 14 13T Ownership 11 7T P Page buffer cost of nonsequential access 13 18T description of 13 16T effect on performance 13 17T restrictions with BLOB data 10 19T
197. S_ORIGIN keyword 1 225S syntax 1 217S Global transaction 12 21T GOTO keyword in the WHENEVER statement 1 398S GRANT statement automated 11 13T changing grantor 1 238S creating a privilege chain 1 238S database level privileges 1 232S 11 5T default table privileges 1 2375 in 4GL 11 13T in embedded SQL 5 34T to 5 37T passing grant ability 1 237S privileges on a view 1 239S syntax 1 231S table level privileges 1 235S 11 7T use of dbschema 5 34R with CREATE SCHEMA 1 775 GROUP BY clause 1 1255 GROUP BY keywords column number with 3 7T composite index used for 13 31T description of 3 4T indexes for 13 10T 13 34T restrictions in modifiable view 11 24T sorting rows 13 12T syntax in SELECT 1 310S use in SELECT 1 334S H HAVING keyword description of 3 9T syntax in SELECT 1 310S use in SELECT 1 336S Header of a procedure 14 25T HEX function 1 435S syntax in expression 1 452S use in expression 1 4525 HIGH keyword 1 3745 Hold cursor definition of 1 149S 7 18T insert cursor with hold 1 157S use of 1 150S Host machine 12 8T Host variable delimiter for 5 6T description of 5 6T dynamic allocation of 5 33T Index 21 fetching data into 5 21T in DELETE statement 6 4T in INSERT 6 8T in UPDATE 6 14T in WHERE clause 5 14T INTO keyword sets 5 13T null indicator 5 15T restrictions in prepared statement 5 29T truncation signalled 5 12T using non English characters in 1 22R with EXECUTE 5 31T HOUR keyword syntax in DATET
198. Sally Cox Signe Haugen Geeta Karmarkar Steven Klitzing Judith Sherwood Rob Weinberg Chris Willis Eileen Wollam RESTRICTED RIGHTS LEGEND The Informix software and accompanying materials are provided with Restricted Rights Use duplication or disclosure by the Government is subject to restrictions as set forth in subdivision c 1 ii of the Rights in Technical Data and Computer Software Clause at DFARS 252 227 7013 or subparagraphs c 1 and 2 of the Commercial Computer Software Restricted Rights at 48 CFR 52 227 19 as applicable and any other applicable license provisions set forth in the Government contract Copyright 1981 1994 by Informix Software Inc Preface This book is a tutorial on the Structured Query Language SQL as it is implemented by Informix products The Informix Guide to SQL Tutorial and its companion volumes the Informix Guide to SQL Reference and the Informix Guide to SQL Syntax tell you how to create manage and use relational databases with Informix software tools Examples in this manual represent a number of Informix products and operating systems at different release levels You must have the following Informix software An INFORMIX OnLine Dynamic Server database server or an INFORMIX SE database server The database server either must be installed on your machine or on another machine to which your machine is connected over a network e Either an Informix application development to
199. Schema Editor the result is displayed in a column labeled expression as shown in Query Result 2 37 stock_num 1 1 4 4 7 8 102 111 112 rS 203 description baseball gloves baseball gloves football football basketball volleyball bicycle brakes 10 spd assmbld 12 spd assmbld 18 spd assmbld irons wedge Query Result 2 37 unit case case case case case case case each each each case unit_descr 10 gloves case 10 gloves case 24 case 24 case 24 case 24 case 4 sets case each each each 2 sets case unit_price 800 450 960 480 600 840 480 499 549 685 670 00 expression 856 481 1027 513 642 898 513 534 587 733 716 0000 5000 2000 6000 0000 8000 6000 9893 4300 9130 9000 Query 2 38 calculates a surcharge of 6 50 on orders when the quantity ordered is less than 5 SELECT item_num total_price FROM items WHERE quantity lt 5 order_num total_price 6 50 quantity Query 2 38 Composing Simple SELECT Statements 2 47 Single Table SELECT Statements If you are using DB Access or INFORMIX SQL the result is displayed in a column labeled expression as shown in Query Result 2 38 item_num order_num quantity total_price expression a 1001 1 250 00 256 50 1 1002 i 960 00 966 50 2 1002 1 240 00 246 50 1 1003 1 20 00 26 50 2 1003 1 840 00 846 50 1 1004 1 250
200. See CREATE TRIGGER in Chapter 1 of the Informix Guide to SQL Syntax for more information on the WHEN condition Using Stored Procedures as Triggered Actions Probably the most powerful feature of triggers is the ability to call a stored procedure as a triggered action The EXECUTE PROCEDURE statement which calls a stored procedure enables you to pass data from the triggering table to the stored procedure and also to update the triggering table with data 15 10 Creating and Using Triggers Using Triggered Actions returned by the stored procedure SPL also lets you define variables assign data to them make comparisons and use procedural statements to accomplish complex tasks within a triggered action Passing Data to a Stored Procedure You can pass data to a stored procedure in the argument list of the EXECUTE PROCEDURE statement The EXECUTE PROCEDURE statement in the follow ing trigger example passes values from the quantity and total_price columns of the items table to the stored procedure calc_totpr CREATE TRIGGER upd_totpr UPDATE OF quantity ON items REFERENCING OLD AS pre_upd NEW AS post_upd FOR EACH ROW EXECUTE PROCEDURE calc_totpr pre_upd quantity post_upd quantity pre_upd total_price INTO total_price Passing data to a stored procedure allows you to use it in the operations that the procedure performs Using the SPL The EXECUTE PROCEDURE statement in the preceding trigger calls the stored procedu
201. T sequential 1 149S 5 23T 5 25T statement as trigger event 1 112S using with transactions 1 155S with DELETE 1 159S INTO keyword in SELECT 1 319S prepared statements 1 148S 5 32T WITH HOLD 7 18T 10 34T See also CLOSE statement See also Hold cursor See also Insert cursor See also OPEN statement See also Scroll cursor See also Select cursor See also Sequential cursor See also Update cursor Cursor Stability isolation level 1 3675S 7 11T CURSOR STABILITY keywords syntax in SET ISOLATION 1 366S Cursory procedure 2 215 customer table in stores6 database columns in A 2R cust_calls table in stores6 database columns in A 5R Cyclic query 4 22T D Daemon 12 14T Data connecting to 12 12T containing foreign characters 1 19R inserting with the LOAD statement 1 255S integrity 12 20T Data access statements 1 6S Data definition statements 1 5S 5 34T Data distributions confidence 1 397S creating on filtered columns 13 9T 13 29T on temporary tables 1 397S RESOLUTION 1 396S 1 397S use with optimizer 13 9T DATA field setting with SET DESCRIPTOR 1 3575 Data integrity 4 22T to 4 25T 12 20T statements 1 6S Data manipulation statements 1 65 Data model attribute 8 14T building 8 3T to 8 33T defining relationships 8 8T denormalizing 10 26T to 10 32T description of 1 3T 8 3T entity relationship 8 4T many to many relationship 8 11T one to many relationship 8 11T one to one relationship 8 11T See also Relational m
202. T 2 49T Display schema for a database 5 34R DISTINCT keyword relation to GROUP BY 3 5T restrictions in modifiable view 11 24T syntax in CREATE INDEX 1 63S in expression 1 462S in SELECT 1 312S use in CREATE INDEX 1 64S in SELECT 1 3138 2 19T no effect in subquery 1 4145 with COUNT function 2 54T Distributed deadlock 7 15T Distributed processing 12 8T Distributions dropping with DROP DISTRIBUTIONS clause 1 396S privileges required to create 1 396S using the HIGH keyword 1 396S using the MEDIUM keyword 1 397S Division symbol arithmetic operator 1 431S DML statements summary 1 65 DOCUMENT keyword use in stored procedures 14 6T Documentation notes Intro 8R Intro 115S 6T Dominant table 3 21T Dormant connection 1 1695 DOS operating system 12 4T DOUBLE PRECISION data type See FLOAT data type DROP AUDIT statement 1 171S DROP CONSTRAINT keywords syntax in ALTER TABLE 1 158 use in ALTER TABLE 1 325 DROP DATABASE statement 1 1725 DROP INDEX statement locks table 7 7T releasing an index 13 34T syntax 1 174S DROP keyword syntax in ALTER TABLE 1 15S use in ALTER TABLE 1 268 DROP SYNONYM statement 1 177S DROP TABLE statement 1 179S DROP TRIGGER statement syntax 1 181S use of 1 181S DROP VIEW statement 1 183S Duplicate index keys 10 22T Duplicate values finding 3 16T in a query 1 313S Dynamic management statements 1 65 Dynamic SQL cursor use with 5 32T description of 5 5T 5 28T freeing prep
203. T DESCRIPTOR 1 2135 SET DESCRIPTOR statement 1 357S X Open specification of NLS 1 15R Y YEAR function as time function 2 56T syntax in expression 1 454S use in expression 1 456S YEAR keyword syntax in DATETIME data type 1 4285 in INTERVAL data type 1 485S use as DATETIME field qualifier 3 8R 1 488S as INTERVAL field qualifier 3 13R 1 491S Symbols INFORMIXDIR etc sqlhosts 12 15T percent sign wildcard in Condition segment 1 410S space as delimiter in DATETIME 3 9R in INTERVAL 3 15R asterisk arithmetic operator 1 431S use in SELECT 1 3125 plus sign arithmetic operator 1 431S hyphen as delimiter in DATETIME 3 9R in INTERVAL 3 15R minus sign arithmetic operator 1 431S 4 4R decimal point as delimiter in DATETIME 3 9R in INTERVAL 3 15R ellipses wildcard in Condition segment 1 4115 etc hosts 12 15T etc services 12 15T division symbol arithmetic operator 1 431S slash arithmetic operator 1 431S colon as delimiter in DATETIME 3 9R in INTERVAL 3 15R equals relational operator 2 30T 2 71T question mark as placeholder in PREPARE 1 2738 5 29T naming variables in PUT 1 287S replacing with USING keyword 1 268S wildcard in Condition segment 1 4115 at sign in database name 1 421S backslash as escape character with LIKE 1 410S with MATCHES 1 411S caret wildcard in Condition segment 1 411S _ underscore wildcard in Condition segment 1 410S
204. T Statements For details on external tables external databases and networks see Chapter 12 Understanding Informix Networking in this manual and Chapter 1 in the Informix Guide to SQL Syntax SELECT FROM sloth meerkat stock WHERE manu_code LIKE _R_ AND unit_price gt 100 ORDER BY description unit_price SELECT FROM sloth meerkat stock WHERE manu_code MATCHES R AND unit_price gt 100 ORDER BY description unit_price Query 2 30 Each statement in Query 2 30 retrieves only those rows for which the middle letter of the manu_code is R as shown in Query Result 2 30 stock_num manu_code description unit_price unit unit_descr 205 HRO 3 golf balls 312 00 case 24 case 2 HRO baseball 126 00 case 24 case 1 HRO baseball gloves 250 00 case 10 gloves case 7 HRO basketball 600 00 case 24 case 102 PRC bicycle brakes 480 00 case 4 sets case 114 PRC bicycle gloves 120 00 case 10 pairs case 4 HRO football 480 00 case 24 case 110 PRC helmet 236 00 case 4 case 110 HRO helmet 260 00 case 4 case 307 PRC infant jogger 250 00 each each 306 PRC tandem adapter 160 00 each each 308 PRC twin jogger 280 00 each each 304 HRO watch 280 00 box 10 box Query Result 2 30 The comparison _R_ for LIKE or R for MATCHES specifies from left to right the following items e Any single character The letter R e Any single character Composing Simple SELECT Statements 2 39 Single
205. T Statements 2 13 Single Table SELECT Statements An implicit select list uses the symbol as shown in Query 2 7b SELECT FROM manufact ORDER BY lead_time Query 2 7b Query 2 7a and Query 2 7b produce the same display Query Result 2 7 shows a list of every column and row in the manufact table in order of lead_time manu_code manu_name lead_time SMT Smith 3 HRO Hero 4 HSK Husky 5 ANZ Anza 5 NRG Norge 7 NKL Nikolus 8 PRC ProCycle 9 KAR Karsten 21 SHM Shimara 30 Query Result 2 7 Ascending Order The retrieved data is sorted and displayed by default in ascending order Ascending order is uppercase A to lowercase z for CHARACTER data types and lowest to highest value for numeric data types DATE and DATETIME type data are sorted from earliest to latest and INTERVAL data is ordered from shortest to longest span of time Descending Order Descending order is the opposite of ascending order from lowercase z to uppercase A for character types and highest to lowest for numeric data types DATE and DATETIME data are sorted from latest to earliest and INTERVAL data is ordered from longest to shortest span of time Query 2 8 shows an example of descending order SELECT FROM manufact ORDER BY lead_time DESC Query 2 8 2 14 Composing Simple SELECT Statements Single Table SELECT Statements The keyword DESC following a column name causes the retrieved data to be sorted in descending order as shown i
206. Table SELECT Statements WHERE Clause with Restricted Single Character Wildcard Query 2 31 selects only those rows where the manu_code begins with A through H and returns the rows shown in Query Result 2 31 The class test A H specifies any single letter from A through H inclusive No equivalent wildcard symbol exists for the LIKE keyword SELECT FROM stock WHERE manu_code MATCHES A H ORDER BY description manu_code unit_price Query 2 31 stock_num manu_code description unit_price unit unit_descr 205 ANZ 3 golf balls 312 00 case 24 case 205 HRO 3 golf balls 312 00 case 24 case 2 HRO baseball 126 00 case 24 case 3 HSK baseball bat 240 00 case 12 case 1 HRO baseball gloves 250 00 case 10 gloves case 1 HSK baseball gloves 800 00 case 10 gloves case 7 HRO basketball 600 00 case 24 case 110 ANZ helmet 244 00 case 4 case 110 HRO helmet 260 00 case 4 case 110 HSK helmet 308 00 case 4 case 301 ANZ running shoes 95 00 each each 301 HRO running shoes 42 50 each each 313 ANZ swim cap 60 00 box 12 box 6 ANZ tennis ball 48 00 case 24 cans case 5 ANZ tennis racquet 19 80 each each 8 ANZ volleyball 840 00 case 24 case 9 ANZ volleyball net 20 00 each each 304 ANZ watch 170 00 box 10 box 304 HRO watch 280 00 box 10 box Query Result 2 31 2 40 Composing Simple SELECT Statements Single Table SELECT Statements WHERE Clause with Variable Length Wildcard The statements in Query 2 32 use a wild
207. The Database Software NLS Databases The Version 6 0 Informix database servers provide Native Language Support NLS This allows you to work in various European or Latin American lan guages other than English and conform to the customs of a specific locale various money and date formats foreign characters in data or identifier names different collation order and so on You can activate the NLS func tionality by setting the DBNLS environment variable as well as other NLS specific environment variables Chapter 4 of the Informix Guide to SQL Reference describes how to set the NLS environment variables For additional information on NLS databases see Chapter 1 in the Informix Guide to SQL Reference The Database Software You access your database through two layers of sophisticated software The top layer or application sends commands or queries to the database server The application calls on the bottom layer or database server and gets back information You command both layers using SQL The Applications A database application or simply application is a program that uses the database It does so by calling on the database server At its simplest the application sends SQL commands to the database server and the database server sends rows of data back to the application Then the application displays the rows to you its user Alternatively you command the application to add new data to the database It incorporates th
208. The slowest thing a disk does is to seek that is to move the access arm to the track holding the data Seek time depends on the speed of the disk and the location of the disk arm when the operation starts Seek time varies from zero to a large fraction of a second Latency The transfer cannot start until the beginning of the page rotates under the access arm This latency or rotational delay depends on the speed of the disk and on the position of the disk when the operation starts Latency can vary from zero to a few milliseconds The time cost of reading a page can vary from microseconds for a page in a buffer to a few milliseconds when contention is zero and the disk arm is already in position to hundreds of milliseconds The Cost of Sequential Access Disk costs are lowest when the database server reads the rows of a table in physical order When the first row on that page is requested its disk page is read Requests for subsequent rows are satisfied from the buffer until the entire page is used As a result each page is read only once Provided that the database server is the only program using the disk the seek time cost is also minimized The disk pages of consecutive rows are usu ally in consecutive locations on the disk so the access arm moves very little from one page to the next Even when that is not the case groups of consec utive pages are usually located together so that only a few long seeks are needed For examp
209. Trapping an Error and Recovering 14 28 Scope of Control of an ON EXCEPTION Statement 14 29 User Generated Exceptions 14 30 Summary 14 33 Creating and Using Triggers Chapter Overview 15 3 When to Use Triggers 15 3 How to Create a Trigger 15 4 Assigning a Trigger Name 15 5 Specifying the Trigger Event 15 5 Defining the Triggered Actions 15 6 A Complete CREATE TRIGGER Statement 15 6 Table of Contents XV Using Triggered Actions 15 7 Using BEFORE and AFTER Triggered Actions 15 7 Using FOR EACH ROW Triggered Actions 15 8 Using Stored Procedures as Triggered Actions 15 10 Tracing Triggered Actions 15 12 Generating Error Messages 15 14 Applying a Fixed Error Message 15 15 Generating a Variable Error Message 15 16 Summary 15 17 Index xvi Table of Contents Introduction Introduction Informix Products That UseSQL 3 Products Included in This Manual 3 Other Useful Documentation 4 How to Use This Manual 5 Typographical Conventions 5 Example Code Conventions 5 Useful On Line Files 6 ASCII and PostScript Error Message Files 7 The Demonstration Database 7 Creating the Demonstration Database 8 Compliance with Industry Standards 9 New Features in Informix Version 6 0 Products That UseSQL 10 2 Introduction Structured Query Language SQL is an English like language that you can use when creating managing and using relational databases The SQL provided with Informix products is an enhanced version of the industr
210. U S and other curren cies are written with two digits to the right of the decimal point Normally 9 10 Implementing Your Data Model Figure 9 2 Defining the Domains you also know the number of digits needed on the left depending on whose transactions are recorded perhaps 5 digits for a personal budget 7 for a small business and 12 or 13 for a national budget These numbers are fixed point numbers because the decimal point is fixed at a specific place regardless of the value of the number The DECIMAL p s data type is designed to hold them When you specify a column of this type you write its precision p as the total number of digits it can store from 1 to 32 You write its scale s as the number of those digits that fall to the right of the dec imal point The relation between precision and scale is diagrammed in Fig ure 9 2 Scale can be zero meaning it stores only whole numbers When this is done DECIMAL p s provides a way of storing integers of up to 32 digits ye precision 8 a DECIMAL 8 3 31964 535 ares 3 digits The relation between precision and scale in a fixed point number As with the DECIMAL p data type DECIMAL p s takes up space in proportion to its precision One value occupies 1 p 2 bytes rounded up toa whole number of bytes The MONEY type is identical to DECIMAL p s but with one extra feature Whenever the database server converts a MONEY value to characters for display it a
211. XEC The program that uses this cursor can fetch rows in the usual way EXEC SQL FETCH names INTO FNAME LNAME COMPANY END EXEC If the program then decides that the row needs to be changed it can do so IF COMPANY IS EQUAL TO SONY EXEC SOL UPDATE customer SET fname Midori lname Tokugawa WHERE CURRENT OF names END EXEC The words CURRENT OF names take the place of the usual test expressions in the WHERE clause In other respects the UPDATE statement is the same as usual even including the specification of the table name which is implicit in the cursor name but still required The Purpose of the Keyword UPDATE The purpose of the keyword UPDATE in a cursor is to let the database server know that the program can update or delete any row that it fetches The database server places a more demanding lock on rows that are fetched through an update cursor and a less demanding lock when fetching a row for a cursor that is not declared with that keyword This results in better perfor mance for ordinary cursors and a higher level of concurrent use in a multiprocessing system Levels of locks and concurrent use are discussed in Chapter 7 Programming for a Multiuser Environment Modifying Data Through SQL Programs 6 15 Using UPDATE Updating Specific Columns You can declare a cursor to update specific columns Here is a revision of the preceding ESQL COBOL ex
212. XECUTE PROCEDURE to execute a procedure from a procedure Figure 14 11 shows a call to the read_name procedure using a CALL statement CREATE RETURNING CHAR 15 PROCEDURE call_test CHAR 15 DEFINE fname lname CHAR 15 CALL read_name Putnum RETURNING fname lname IF fname Hileen THEN RETURN Jessica lname ELSE RETURN fname lname END IF END PROCEDURE Calling a procedure with a CALL statement Running an Operating System Command from Within a Procedure Figure 14 12 Use the SYSTEM statement to execute a system call from a procedure Figure 14 12 shows a call to the echo command CREATE DBA PROCEDURE delete_customer cnum INT DEFINE username CHAR 8 DELETE FROM customer WHERE customer_num cnum acctclrk THEN Delete from customer by acctclrk gt gt mis records updates IF username SYSTEM echo END IF END PROCEDURE delete_customer Making a system call from a procedure with a SYSTEM statement Recursively Calling a Procedure You can call a procedure from itself No restrictions apply on calling a procedure recursively 14 24 Creating and Using Stored Procedures Passing Information into and out of a Procedure Passing Information into and out of a Procedure When you create a procedure you determine whether it expects information to be passed to it by specifying an argument list For each piece of informa tion that the procedure expects you
213. Y clause without aggregates is much like using the DISTINCT or UNIQUE keyword in the SELECT clause Chapter 2 Compos ing Simple SELECT Statements included the statement found in Query 3 1a SELECT DISTINCT customer_num FROM orders Query 3 1a You also could write the statement as shown in Query 3 1b SELECT customer_num FROM orders GROUP BY customer_num Query 3 1b Query 3 1a and Query 3 1b return the rows shown in Query Result 3 1 customer_num L01 L04 L06 L10 L11 L12 L15 L16 L17 119 L20 21 22 23 L24 L26 L27 Query Result 3 1 The GROUP BY clause collects the rows into sets so that each row in each set has equal customer numbers With no other columns selected the result is a list of the unique customer_num values The power of the GROUP BY clause is more apparent when you use it with aggregate functions Composing Advanced SELECT Statements 3 5 Using the GROUP BY and HAVING Clauses Query 3 2 retrieves the number of items and the total price of all items for each order SELECT order_num COUNT number SUM total_price price FROM items GROUP BY order_num Query 3 2 The GROUP BY clause causes the rows of the items table to be collected into groups each group composed of rows that have identical order_num values that is the items of each order are grouped together After you form the groups the aggregate functions COUNT and SUM are applied within each
214. _date gt main ship_date AND ship_date IS NOT NULL ORDER BY ship_date po_num Query 3 31 The subquery is correlated because the number it produces depends on main ship_date a value produced by the outer SELECT Thus the subquery must be executed anew for every row that the outer query considers Composing Advanced SELECT Statements 3 37 Subqueries in SELECT Statements Query 3 31 uses the COUNT function to return a value to the main query The ORDER BY clause then orders the data The query locates and returns the 13 rows that have the 10 latest shipping dates as shown in Query Result 3 31 po_num ship_date 4745 06 21 1993 278701 06 29 1993 4290 06 29 1993 8052 07 03 1993 B77897 07 03 1993 LZ230 07 06 1993 B77930 07 10 1993 PC6782 07 12 1993 DM354331 07 13 1993 S22942 07 13 1993 A003 07 16 1993 W2286 07 16 1993 Z55709 07 16 1993 C3288 07 25 1993 KF 2961 07 30 1993 w9925 07 30 1993 Query Result 3 31 If you use a correlated subquery such as Query 3 31 on a very large table you should index the ship_date column to improve performance Otherwise this SELECT statement might be considered somewhat inefficient because it executes the subquery once for every row of the table Indexing and performance issues are discussed in Chapter 10 Tuning Your Data Model Using EXISTS The keyword EXISTS is known as an existential qualifier because the subquery is true only if the outer SELECT shown in Query
215. _descr Order placed one month ago 6 7 not received res_dtime 993 07 07 10 30 res_descr Checked with shipping Ed Smith Order sent yesterday we were waiting for goods from ANZ Next time will call with delay if necessary customer_num 19 call_dtime 993 07 01 15 00 user_id riche call_code B call_descr Bill does not reflect credit from previous order res_dtime 993 07 02 08 21 res_descr Spoke with Jane Akant in Finance She found the error and is sending new bill to customer Query Result 2 65 2 64 Composing Simple SELECT Statements Single Table SELECT Statements Query 2 66 if issued when today s system date is July 10 1993 returns this one row SELECT FROM orders WHERE order_date TODAY Query 2 66 order_num 1018 order_date 07 10 1993 customer_num 121 ship_instruct SW corner of Biltmore Mall backlog n po_num S22942 ship_date 07 13 1993 ship_weight 70 50 ship_charge 20 00 paid_date 08 06 1993 Query Result 2 66 You can include the keyword DBSERVERNAME or its synonym SITENAME in a SELECT statement on INFORMIX OnLine Dynamic Server to find the name of the database server You can query on the DBSERVERNAME for any table that has rows including system catalog tables In Query 2 67 you assign the label server to the DBSERVERNAME expression and also select the tabid column from the systables system catalog table This table describes database tables and tabid is the serial inter
216. _num CHAR 13 PRIMARY KEY rec_num INT b_type CHAR 5 FOREIGN KEY rec_num REFERENCES name i rec_num rec_num rec_num fax_num rec_num rec_num The CREATE TABLE statements for the telephone directory data model Implementing Your Data Model 9 25 Creating the Database Using Command Scripts You can create the database and tables by entering the statements interactively But what if you have to do it again or several more times You might have to do it again to make a production version after a test version is satisfactory You might have to implement the same data model on several machines To save time and reduce the chance of errors you can put all the commands to create a database in a file and execute them automatically Capturing the Schema You can write the statements to implement your model into a file yourself However you can also have a program do it for you See Chapter 5 of the Informix Guide to SQL Reference It documents the dbschema utility a pro gram that examines the contents of a database and generates all the SQL state ments required to re create it You can build the first version of your database interactively making changes until it is exactly as you want it Then you can use dbschema to generate the SQL statements necessary to duplicate it Executing the File DB Access or INFORMIX SQL the programs you use to enter SQL statements interactively can be driven from a file
217. a possible consistent with the preceding goal Concurrency Issues To understand the hazards of concurrency you must think in terms of multiple programs each executing at its own speed The following example suppose that your program is fetching rows through the following cursor DECLARE sto_curse CURSOR FOR SELECT FROM stock WHERE manu_code ANZ The transfer of each row from the database server to the program takes time During and between transfers other programs can perform other database operations Say that at about the same time your program fetches the rows produced by that query another user s program executes the following update UPDATE stock SET unit_price 1 15 unit_price WHERE manu_code ANZ In other words both programs are reading through the same table one fetching certain rows and the other changing the same rows The following possibilities concerning what happens next 1 The other program finishes its update before your program fetches its first row Your program shows you only updated rows 2 Your program fetches every row before the other program has a chance to update it Your program shows you only original rows 7 4 Programming for a Multiuser Environment How Locks Work 3 After your program fetches some original rows the other program catches up and goes on to update some rows that your program has yet to read then it executes the COMMIT WORK statement Your
218. a structure that can be executed The data structure is associated with a name q_orders 3 A cursor named cu_orders is declared and associated with the name of the prepared statement 4 When the cursor is opened the prepared statement is executed The USING clause in the OPEN statement provides the names of two host vari ables whose contents are substituted for the question marks in the original statement 5 The first row of data is fetched from the open cursor The INTO clause of the FETCH statement specifies the host variables that are to receive the fetched column values Later the cursor can be closed and reopened While the cursor is closed a dif ferent SELECT statement can be prepared under the name q_orders In this way a single cursor can be used to fetch from different SELECT statements 5 32 Programming with SQL Dynamic SQL Dynamic Host Variables In SQL APIs which support dynamically allocated data objects it is possible to take dynamic statements one step further It is possible to dynamically allocate the host variables that receive column data This makes it possible to take an arbitrary SELECT statement from program input determine how many values it produces and their data types and allocate the host variables of the appropriate types to hold them The key to this ability is the DESCRIBE statement It takes the name of a prepared SQL statement and returns information about the statement and its conte
219. a user to modify existing rows The Delete privilege allows a user to delete rows The Select privilege is necessary for a user to retrieve the contents of a table However The Select privilege is not a precondition for the other privileges A user can have Insert or Update privileges without having the Select privilege For example your application might have a usage table Every time a certain program is started it inserts a row into the usage table to document that it was used Before the program terminates it updates that row to show how long it ran and perhaps to record counts of work performed by its user If you want any user of the program to be able to insert and update rows in this usage table you grant Insert and Update privileges on it to public However you might grant the Select privilege to only a few users Index Alter and References Privileges The Index privilege permits its holder to create and alter indexes on the table The Index privilege similar to the Select Insert Update and Delete privileges is granted automatically to public when a table is created 11 8 Granting and Limiting Access to Your Database Granting Privileges Privileges in the System Catalog Privileges are recorded in the system catalog tables Any user with the Connect privilege can query the system catalog tables to determine what privileges have been granted and to whom Database privileges are recorded in the sysusers table
220. abase Server Executing an SQL statement is essentially calling the database server as a subroutine Information must pass from the program to the database server and information must be returned Some of this communication is done through host variables You can think of the host variables named in an SQL statement as the parameters of the proce dure call to the database server In the preceding example a host variable acts as a parameter of the WHERE clause Also as described in Retrieving Multi ple Rows on page 5 19 host variables receive data that is returned by the database server The SQL Communications Area The database server always returns a result code and possibly other informa tion about the effect of an operation in a data structure known as the SOL Communications Area SQLCA If the database server executes an SQL state ment in a stored procedure the SQLCA of the calling application contains the values triggered by the SQL statement in the procedure The principal fields of the SQLCA are listed in Figure 5 4 and Figure 5 5 The syntax you use to describe a data structure such as the SQLCA as well as the syntax you use to refer to a field in it differs among programming languages See your SQL API manual for details You can also use the SQLSTATE variable of the GET DIAGNOSTICS statement to detect handle and diagnose errors See The SOLSTATE Value on page 5 12 5 8 Programming with SQL Calling the
221. abases Changes to tables and views in other databases are not reflected in views Such changes might not be apparent until someone queries the view and gets an error because an external table changed Modifying Through a View It is possible to modify views as if they were tables Some views can be modified and others not depending on their SELECT statements The restric tions are different depending on whether you use DELETE UPDATE or INSERT statements Granting and Limiting Access to Your Database 11 23 Using Views No modification is possible on a view when its SELECT statement contains any of the following features e A join of two or more tables Many anomalies arise if the database server tries to distribute modified data correctly across the joined tables e An aggregate function or the GROUP BY clause The rows of the view represent many combined rows of data the database server cannot distribute modified data into them The DISTINCT keyword or its synonym UNIQUE The rows of the view represent a selection from among possibly many duplicate rows the database server cannot tell which of the original rows should receive the modification When a view avoids all these things each row of the view corresponds to exactly one row of one table Such a view is modifiable Of course particular users can modify a view only if they have suitable privileges Privileges on views are discussed beginning on page 11 27 D
222. able than a program a lack of data can be a normal event Serious Errors Errors that set SQLCODE to a negative value are usually serious Programs which you have developed and are in production should rarely report these errors Nevertheless it is difficult to anticipate every problematic situation so your program must be able to deal with them For example a query can return error 206 which means table name is not in the database This happens if someone dropped the table since the program was written or if through some error of logic or mistake in input the program opened the wrong database Using Default Values You can handle these inevitable errors in many ways In some applications more lines of code to handle errors are used than for normal situations In the examples in this section however one of the simplest methods the default value should work avg_price 0 set default for errors exec sql select avg total_price into avg_price null_flag from items if null_flag lt 0 probably no rows avg_price 0 set default for 0 rows Programming with SQL 5 17 Retrieving Single Rows End of Data with Databases that are not ANSI Compliant If your database is not ANSI compliant the end of data return code 100 is set in SQLCODE only following SELECT statements In addition the SQL STATE value is set to 02000 Other statements such as INSERT UPDATE and DELETE set the third eleme
223. ach data item and specifies its meaning with respect to the other items and to the real world A database can be used and even modified by several computer users working concurrently Different users can be given different views of the con tents of a database and their access to those contents can be restricted in several ways 1 18 Introducing Database Features and SQL Summary A database can be crucially important to the success of an organization and can require central administration and monitoring The INFORMIX OnLine Dynamic Server database server caters to the needs of essential applications both OnLine and INFORMIX SE support smaller databases for private or group use You manipulate and query a database using SQL which was pioneered by IBM and standardized by ANSI You can take advantage of the Informix extensions to the ANSI defined language and your Informix tools also make it possible to maintain strict compliance with ANSI standards Two layers of software mediate all your work with databases The bottom layer is always a database server that executes SQL statements and manages the data on disk and in computer memory The top layer is one of many appli cations some from Informix and some written by you or written by other vendors or your colleagues Introducing Database Features and SQL 1 19 Summary 1 20 Introducing Database Features and SQL Chapter Composing Simple SELECT Statements Chapter Overview
224. action processing are also enforced See the discussion of ANSI SQL in Chapter 1 of the Informix Guide to SQL Reference CREATE DATABASE std_rules_db WITH LOG MODE ANSI The design of ANSI SQL prohibits the use of buffered logging The OnLine administrator can turn transaction logging on and off later For example it can be turned off before inserting a large number of new rows Using CREATE DATABASE with Other Informix Database Servers Other Informix database servers create a database as a set of one or more files managed by the operating system For example under the UNIX operating system a database is a small group of files in a directory whose name is the database name See the manual for your database server for details on how it uses files This means that the rules for database names are the same as the rules the operating system has for file names Choosing the Type of Logging Other database servers offer the following three choices of logging No logging at all This choice is not recommended if the database is lost to a hardware failure all data alterations since the last archive are lost CREATE DATABASE not_logged_db When you do not choose logging BEGIN WORK and other SQL statements related to transaction processing are not permitted in the database This affects the logic of programs that use the database e Regular logging This is the best choice for most databases If the database is lost only
225. actions See CREATE TRIGGER in Chapter 1 of the Informix Guide to SQL Syntax for more information on what happens when a trigger fails Using FOR EACH ROW Triggered Actions A FOR EACH ROW triggered action executes once for each row that the triggering statement effects For example if the triggering statement is has the following syntax UPDATE items SET quantity quantity 2 WHERE manu_code KAR A FOR EACH ROW triggered action executes once for each row in the items table in which the manu_code column has a value of KAR If the triggering statement does not process any rows a FOR EACH ROW triggered action does not execute 15 8 Creating and Using Triggers Using Triggered Actions Using the REFERENCING Clause When you create a FOR EACH ROW triggered action you must usually indicate in the triggered action statements whether you are referring to the value of a column before or after the effect of the triggering statement For example imagine that you want to track updates to the quantity column of the items table To do this you create the following table to record the activity CREATE TABLE log_record item_num SMALLINT ord_num INTEGER username CHARACTER 8 update_time DATETIME YEAR TO MINUTE old_qty SMALLINT new_qty SMALLINT To supply values for the old_qty and new_qty columns in this table you must be able to refer to the old and new values of quantity in th
226. ages and Disadvantages of a Single User System A configuration involving only one computer is the easiest configuration to set up and maintain and it gives the fastest access to data However the data is not available to users on other computers and the size of the databases or the amount of processing needed may outgrow the capacity of the computer A Local Multiuser Configuration Figure 12 2 shows another database management system configuration a multiuser system with a local database server such as one you might find on a computer with a UNIX operating system UNIX computer a databases CG application database server Figure 12 2 A database management system on a UNIX computer 12 6 Understanding Informix Networking Database Management System Configurations The components of the systems in Figure 12 2 are similar to the components in Figure 12 1 as described in the following list e Application programs Two or more applications use the same database server to access informa tion in the databases You might have two users at individual terminals as shown or you might have multiple windows on a single workstation e A connection On a local UNIX system the following types of connection are possible o Inter process communication IPC o Network connection IPC is a UNIX feature that transfers information very quickly between the application and the database server It is available only when the a
227. although it may run more slowly on the net work database As long as the data model is the same a program cannot tell the difference between a local database server and a remote one Protecting Your Data in a Networked Environment This section gives an overview of data protection features used on a network Chapter 4 Modifying Data has a general discussion of data protection Data Protection with INFORMIX SE INFORMIX SE databases use the normal UNIX file structures so SE databases can be archived with the usual operating system backup procedures On a network you can write the archives to a device in another location Data Protection with INFORMIX OnLine Dynamic Server OnLine includes several different tools that make multiple copies of data Each one has its own unique task in the area of data protection The following discussions give a general description of these tools and highlight the distinctions between them Data Replication Ina general sense data replication means that a given piece of data has several distinct representations on several distinct servers OnLine does data replica tion by using two networked computers Each computer has an OnLine Understanding Informix Networking 12 19 Protecting Your Data in a Networked Environment database server and databases that have identical characteristics One data base server is the primary and the other is the secondary Data is always writ ten to the primary
228. ample has been modified to use this feature and is shown in the following example EXEC SQL DECLARE names CURSOR FOR SELECT fname lname company phone INTO FNAME LNAME COMPANY PHONE FROM customer FOR UPDATE OF fname lname END EXEC Only the fname and Iname columns can be updated through this cursor A statement such as the following one is rejected as an error EXEC SOL UPDATE customer SET company Siemens WHERE CURRENT OF names END EXEC If the program attempts such an update an error code is returned and no update takes place An attempt to delete using WHERE CURRENT OF is also rejected because deletion affects all columns UPDATE Keyword Not Always Needed The ANSI standard for SQL does not provide for the FOR UPDATE clause in a cursor definition When a program uses an ANSI compliant database it can update or delete using any cursor Cleaning up a Table A final hypothetical example of using an update cursor presents a problem that should never arise with an established database but could arise in the initial design phases of an application A large table named target for example is created and populated A character column datcol inadvertently acquires some null values These rows should be deleted Furthermore a new column serials is added to the 6 16 Modifying Data Through SQL Programs Summary Figure 6 6 Summary table with the ALTER TABLE s
229. an update a blob column to null or to a subquery returning a blob column TEXT values are not stored with the rows of which they are a part They are allocated in whole disk pages usually areas away from rows See Locating Blob Data on page 10 18 The advantage of the TEXT data type over CHAR n and VARCHAR m r is that the size of a TEXT data item has no limit except the capacity of disk storage to hold it The disadvantages of the TEXT data type are found in the following list Itis allocated in whole disk pages a short item wastes space Restrictions apply on how you can use a TEXT column in an SQL statement See How Blobs Are Used on page 9 18 9 18 Implementing Your Data Model Defining the Domains e It is not available with all Informix database servers You can display TEXT values in reports generated with INFORMIX 4GL programs or the ACE report writer You can display TEXT values on a screen and edit them using screen forms generated with INFORMIX 4GL programs or with the PERFORM screen form processor Binary Objects BYTE The BYTE data type is designed to hold any data a program can generate graphic images program object files and documents saved by any word pro cessor or spreadsheet The database server permits any kind of data of any length in a BYTE column As with TEXT BYTE data items are stored in whole disk pages in separate disk areas from normal row data The advantage of the BYT
230. aptable to various European cultural and language environments without requiring changes to the application source code When appropriate environment variables are set to activate NLS and specify a locale Informix products can properly collate strings that con tain foreign characters accept money and decimal input and print dates and times in the format required by the locale where the software is run The user can o Create or access database information in any language available on the system by changing a few environment variables o Name user defined objects such as databases tables columns views cursors and files using a foreign character set o Use the new NCHAR and NVARCHAR data types in place of CHAR and VARCHAR respectively for storing national characters In addition by installing one or more language supplements with an Informix product the user can view error and warning messages in the language of the locale Enhanced Database Connections You can now use three new statements CONNECT TO DISCONNECT and SET CONNECTION to provide a connection oriented association between client and server processes in a networked or a non networked environ ment These three statements are compliant with X Open and ANSI ISO specifications Applications with embedded SQL can use these statements for more uniform and portable syntax when accessing local or remote data Cascading Deletes Support for cascading deletes is provided
231. apter 13 Optimizing Your Queries which deals with making queries faster Sometimes you also must consider making queries do less that is reducing the functions available to on line users You can look for any allowed transaction that entails scanning an entire large table such as any kind of summation average or management report especially if it requires a join Consider removing such transactions from on line programs Instead offer a new facility that interactively schedules an off peak job with the output returned the next day Tuning Your Data Model Maximizing Concurrency Rescheduling Modifications To the greatest extent possible schedule modifications for times when no interactive users are using the database One reason for this is that concurrent modifications must be done with all indexes in place that means they incur all the time costs noted earlier Another reason is that modifications not only lock table rows they also lock index pages That increases the number of locks in use and the number of lock delays for all users The means of rescheduling modifications depend entirely on the details of your application Using an Update Journal Instead of performing updates as the data becomes available consider creating an update journal This is a table that contains rows that represent pending updates Its rows contain the following information e Data items to be changed in some base table with null meanin
232. are using other database servers use operating system commands to back up the files that represent the database Restore transaction logging and release the exclusive lock on the database You can enclose the steps of populating a database in a script of operating system commands You can automate the INFORMIX OnLine Dynamic Server administrator commands by invoking the command line equivalents to ON Monitor This chapter covered the following work which you must do to implement a data model Specify the domains or constraints that are used in the model and complete the model diagram by assigning constraints to each column Use interactive SQL to create the database and the tables in it If you must create the database again write the SQL statements to do so into a script of commands for the operating system Populate the tables of the model first using interactive SQL and then by bulk operations Possibly write the bulk load operation into a command script so you can repeat it easily You can now use and test your data model If it contains very large tables or if you must protect parts of it from certain classes of users more work remains to be done That is the subject of Chapter 10 Tuning Your Data Model Implementing Your Data Model 9 29 Summary 9 30 Implementing Your Data Model Chapter 10 Tuning Your Data Model Chapter Overview 3 INFORMIX OnLine Dynamic Server Disk Storage 3 Chunks and
233. ared statements 5 33T E Editor specifying with DBEDIT 4 18R Effective checking 1 349S Ellipses wildcard in Condition segment 1 411S Embedded SQL defined 5 3T languages available 5 4T See also ESQL End of data signal in SQLCODE 5 11T 5 17T signal only for SELECT 6 14T when opening cursor 5 20T Entity attributes associated with 8 15T business rules 8 5T criteria for choosing 8 7T defined 8 4T important qualities of 8 5T in telephone directory example 8 7T integrity 4 18T naming 8 4T represented by a table 8 22T Entity occurrence defined 8 16T Entity relationship diagram connectivity 8 17T discussed 8 17T meaning of symbols 8 17T reading 8 18T ENVIGNORE environment variable 4 30R relation to chkenv utility 5 4R Environment configuration file debugging with chkenv 5 4R example 4 4R where stored 4 5R Environment variable and case sensitivity 4 6R ARC_DEFAULT 4 14R ARC_KEYPAD 4 14R COLLCHAR 4 45R DBANSIWARN 4 15R DBAPICODE 4 47R DBAPICODE and crtcmap utility 5 5R DBDATE 4 16R DBDELIMITER 4 18R DBEDIT 4 18R DBLANG 4 19R DBLANG and crtcmap utility 5 5R DBMONEY 4 20R DBNLS 4 48R DBPATH 4 21R 12 14T DBPRINT 4 24R DBREMOTECMD 4 25R DBSPACETEMP 4 26R DBTEMP 4 27R DBTIME 4 27R DBUPSPACE 4 30R default assumptions 4 6R defining in environment configuration file 4 4R definition of 4 3R ENVIGNORE 4 30R ENVIGNORE and chkenv utility 5 4R how to set in Bourne shell 4 5R how to set in C shell 4 5R
234. artments that they manage Then the following view restricts managers to rows that reflect only their employees CREATE VIEW hr_mgr_data AS SELECT FROM hr_data WHERE dept_num SELECT dept_num FROM hr_data WHERE user_id USER AND NOT user_id USER The final condition is required so that the managers do not have update access to their own row of the table It is therefore safe to grant the Update privilege to managers for this view but only on selected columns as shown in this statement GRANT SELECT UPDATE performance_level performance_notes ON hr_mgr_data TO peter_m Summary In a database that contains public material or is used only by you and trusted associates security is not an important consideration and few of the ideas in this chapter are needed But as more people are allowed to use and modify the data and as the data becomes increasingly confidential you must spend more time and be ever more ingenious at controlling the way people can approach the data The techniques discussed here can be divided into the following two groups Keeping data confidential When the database resides in operating system files you can use features of the operating system to deny access to the database In any case you control the granting of the Connect privilege to keep people out of the database When different classes of users have different degrees of authorization you must allow them all
235. ase the orders table has an index zip_ix on the zip code column The following command causes the database server to put the rows of the customer table into descending order by zip code ALTER INDEX zip_ix TO CLUSTER To cluster a table on a nonindexed column you must create an index The following command reorders the orders table by order date CREATE CLUSTERED INDEX o_date_ix ON orders order_date ASC To reorder a table the database server must copy the table In the preceding example the database server reads all rows of the table and constructs an index Then it reads the index entries in sequence For each entry it reads the matching row of the table and copies it to a new table The rows of the new table are in the desired sequence This new table replaces the old table Clustering is not preserved when you alter a table When you insert new rows they are stored physically at the end of the table regardless of their con tents When you update rows and change the value of the clustering column the rows are written back into their original location in the table When clustering is disturbed by updates it can be restored The following command reorders the table to restore the physical sequence ALTER INDEX o_date_ix TO CLUSTER Tuning Your Data Model 10 25 Denormalizing Reclustering is usually quicker than the original clustering because reading out the rows of a nearly clustered tabl
236. assmbld baseball gloves volleyball football unit_price 4 5 19 20 20 23 25 42 45 45 48 48 48 48 308 312 312 312 450 480 480 499 549 600 670 685 800 840 960 Composing Simple SELECT Statements 50 00 80 00 00 00 00 50 00 00 00 00 00 00 00 00 00 00 00 00 00 99 00 00 00 90 00 00 00 unit eac eac eac eac eac eac eac eac eac eac case case box box case case case case case case case each each case case each case case case unit_descr eac eac eac eac eac eac eac eac eac eac 24 cans case 4 case 24 pairs box 4 pairs box 4 case 24 case 24 case 24 case 10 gloves case 24 case 4 sets case each each 24 case 2 sets case each 10 gloves case 24 case 24 case 2 17 Single Table SELECT Statements The order of the columns in the ORDER BY clause is important and so is the position of the DESC keyword Although the statements in Query 2 11 con tain the same components in the ORDER BY clause each produces a different result not shown SELECT FROM stock ORDER BY manu_code unit_price DESC SELECT FROM stock ORDER BY unit_price manu_code DESC SELECT FROM stock ORDER BY manu_code DESC unit_price SELECT FROM stock ORDER BY unit_price DESC manu_code Query 2 11 Sel
237. at object and can alter or drop it without needing additional privileges Table Level Privileges You can apply seven privileges table by table to allow nonowners the privileges of owners Four of them the Select Insert Delete and Update privileges control access to the contents of the table The Index privilege Granting and Limiting Access to Your Database 11 7 Granting Privileges controls index creation The Alter privilege controls the authorization to change the table definition The References privilege controls the authorization to specify referential constraints on a table In an ANSI compliant database only the table owner has any privileges In other databases the database server as part of creating a table automatically grants all table privileges except Alter and References to public This means that a newly created table is accessible to any user with the Connect privilege If this is not what you want if users exist with the Connect privi lege who should not be able to access this table you must revoke all privileges on the table from public after you create the table Access Privileges Four privileges govern how users can access a table As the owner of the table you can grant or withhold the following privileges independently e The Select privilege allows selection including selecting into temporary tables The Insert privilege allows a user to add new rows e The Update privilege allows
238. ata Model has more information on archiving Performance problems that arise in group and private databases are usually related to particular queries that take too long Chapter 13 Optimizing Your Queries deals in depth with the reasons why a query takes more or less time After you understand all the features of the SELECT statement and the alternative ways of stating a query as covered in Chapter 2 Composing Simple SELECT Statements and Chapter 3 Composing Advanced SELECT Statements you can use the tips in Chapter 13 Optimizing Your Queries to improve the performance of queries that otherwise might take excessive amounts of time Essential Databases The INFORMIX OnLine Dynamic Server database server is designed to man age large databases with requirements for high reliability high availability and high performance Although it supports private and group databases very well it is at its best managing the databases that are essential for your organization to carry out its work INFORMIX OnLine Dynamic Server gives you the ability to make archival copies while the databases are in use It also allows incremental archiving archiving only modified data an important feature when making a com plete copy could take many reels of tape INFORMIX OnLine Dynamic Server has an interactive monitor program by which its operator or any user can monitor the activities within the database server to see when bottl
239. ata for display as a report or form on the ter minal screen ACE is the report generator for INFORMIX SQL You provide to ACE a SELECT statement that returns the rows of data and a report specifica tion stating how the pages of the report are to be laid out ACE compiles this information into a program that you can run whenever you want to produce that report PERFORM is the module of INFORMIX SQL that generates interactive screen forms You prepare a form specification that relates display fields on the screen to columns within tables in the database PERFORM compiles this specification into a program that you can run at any time When run the form program interrogates the database to display a row or rows of data on the screen in the format you specified You can arrange the form so that the user can type in sample values and have matching rows returned from the database the query by example feature For more information on these products refer to the manuals that come with them General Programming You can write programs that incorporate SQL statements and exchange data with the database server That is you can write a program to retrieve data from the database and format it however you choose You also can write pro grams that take data from any source in any format prepare it and insert it into the database Introducing Database Features and SQL 1 17 Summary The most convenient programming language for this kind of work
240. ata is defined as shown in Figure 11 1 CREATE TABLE hr_data emp_key INTEGER emp_name CHAR 40 hire_date DATE dept_num SMALLINT user id CHAR 18 salary DECIMAL 8 2 performance_level CHAR 1 performance_notes TEXT Figure 11 1 A table of confidential employee information Because this table contains sensitive data you execute the following statement immediately after creating it REVOKE ALL ON hr_data FROM PUBLIC 11 10 Granting and Limiting Access to Your Database Granting Privileges For selected persons in the Human Resources department and for all managers you execute a statement such as the following one GRANT SELECT ON hr_data TO harold_r In this way you permit certain users to view all columns The final section of this chapter discusses a way to limit the view of managers to only their own employees For the first line managers who carry out performance reviews you could execute a statement such as the following one GRANT UPDATE performance_level performance_notes ON hr_data TO wallace_s margot_t This statement permits the managers to enter their evaluations of their employees Only for the manager of the Human Resources department or whomever is trusted to alter salary levels would you execute a statement such as the following one GRANT UPDATE salary ON hr_data to willard_b For the clerks in the Human Resources department you
241. atabase server tests only the privileges you are granted on the view It does not also test your right to access the underlying tables If you created the view your privileges are the ones noted in the preceding paragraph If you are not the creator you have the privileges that were granted to you by the creator or someone who had the WITH GRANT OPTION privilege The implication of this is that you can create a table and revoke public access to it then you can grant limited access privileges to the table through views This can be demonstrated through the previous examples using the hr_data table Its definition is repeated in Figure 11 9 CREATE TABLE hr_data emp_key INTEGER emp_name CHAR 40 hire_date DATE dept_num SMALLINT user id CHAR 18 salary DECIMAL 8 2 performance_level CHAR 1 performance_notes TEXT A table of confidential employee information duplicate of Figure 11 1 11 28 Granting and Limiting Access to Your Database Privileges and Views In Figure 11 9 the example centered on granting privileges directly on this table The following examples take a different approach Assume that when the table was created the following statement was executed REVOKE ALL ON hr_data FROM PUBLIC This is not necessary in an ANSI compliant database Now you create a series of views for different classes of users For those who should have read only access to the nonsensitive columns you cr
242. atabase with 5 34T 9 26T UNLOAD statement 9 27T INFORMIXSTACKSIZE environment variable 4 38R INFORMIXTERM environment variable 4 38R informix rc file 4 4R Insert buffer counting inserted rows 1 205S 1 290S filling with constant values 1 2865 inserting rows with a cursor 1 2485 storing rows with PUT 1 285S triggering flushing 1 289S Insert cursor 1 148S closing 1 395 definition of 1 148S 6 8T in INSERT 1 248S in PUT 1 286S opening 1 266S reopening 1 2675 result of CLOSE in SQLCA 1 398 use of 1 149S 6 11T with hold 1 157S writing buffered rows with FLUSH 1 204S INSERT INTO keywords in INSERT 1 245S in LOAD 1 258S INSERT keyword syntax in GRANT 1 235S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 302S Insert privilege 11 8T 11 28T INSERT REFERENCING clause and FOR EACH ROW section 1 121S correlation name 1 118S syntax 1 118S INSERT STATEMENT using functions in the VALUES clause 1 252S INSERT statement and end of data 6 14T character position form 5 28R constant data with 6 11T count of rows inserted 6 11T delimiter form 5 24R duplicate values in 4 7T effect of transactions 1 249S embedded 6 8T to 6 14T filling insert buffer with PUT 1 285S in dynamic SQL 1 2535 in trigger event 1 111S in triggered action 1 1225 inserting multiple rows 4 9T nulls with the VALUES clause 1 252S rows 4 6T rows through a view 1 2465 rows with a cursor 1 248S single rows 4 7T values into SERIAL columns 3 19R null values in 4
243. ate NOT IN AZ NJ ORDER BY state Query 2 26 2 34 Composing Simple SELECT Statements iname city Pauli Sunnyvale Sadler San Francisco Currie Palo Alto Higgins Redwood City Vector Los Altos Watson ountain View Ream Palo Alto Quinn Redwood City Miller Sunnyvale Jaeger Redwood City Keyes Sunnyvale Lawson Los Altos Beatty enlo Park Albertson Redwood City Grant enlo Park Parmelee ountain View Sipes Redwood City Baxter Oakland Neelie Denver Wallack Wilmington Hanlon Jacksonville Henry Brighton Satifer Blue Island Putnum Bartlesville Query Result 2 26 Identifying Null Values Use the IS NULL or IS NOT NULL option to check for null values A null represents either the absence of data or a value that is unknown or not Single Table SELECT Statements state phone CA CA CA CA CA CA CA CA CA CA CA CA CA CA CA CA CA CA CO try E OZ x 408 789 8075 415 822 1289 415 328 4543 415 368 1100 415 776 3249 415 389 8789 415 356 9876 415 544 8729 408 723 8789 415 743 3611 408 277 7245 415 887 7235 415 356 9982 415 886 6677 415 356 1123 415 534 8822 415 245 4578 415 655 0011 303 936 7731 302 366 7511 904 823 4239 617 232 4159 312 944 5691 918 355 2074 applicable A null value is not the same as a zero or a blank Query 2 27 returns all rows that have a null paid_date In Query 2 26 by adding the keyword NOTIN the subset changes to exclude the subsets AZ and NJ in
244. ate a database you are the only one who can access it until you as the owner or Database Administrator DBA of the database grant database level privileges to others When you create a table in a database that is not ANSI compliant all users have access privileges to the table until you as the owner of the table revoke table level privileges from specific users The following list contains database level privileges Connect privilege allows you to open a database issue queries and create and place indexes on temporary tables Resource privilege allows you to create permanent tables DBA privilege allows you to perform several additional functions as the DBA Seven table level privileges exist However only the first four are covered here Modifying Data 4 15 Database Privileges Select privilege is granted on a table by table basis and allows you to select rows from a table This privilege can be limited by specific columns in a table Delete privilege allows you to delete rows Insert privilege allows you to insert rows Update privilege allows you to update existing rows that is to change their content The people who create databases and tables often grant the Connect and Select privileges to public so that all users have them If you can query a table you have at least the Connect and Select privileges for that database and table For more information about public see The Users and the Public on page
245. ate an audit trail of activity in the database For example you can track updates to the orders table by updating corroborating information to an audit table Implement a business rule For example you can determine when an order exceeds a customer s credit limit and display a message to that effect Derive additional data that is not available within a table or within the database For example when an update occurs to the quantity column of the items table you can calculate the corresponding adjustment to the total_price column e Enforce referential integrity When you delete a customer for example you can use a trigger to delete corresponding rows that is rows having the same customer number in the orders table Creating and Using Triggers 15 3 How to Create a Trigger How to Create a Trigger You use the CREATE TRIGGER statement to create a trigger The CREATE TRIGGER statement is a data definition statement that associates SQL state ments with a precipitating action on a table When the precipitating action occurs the associated SQL statements which are stored in the database are triggered The following diagram illustrates the relationship of the precipitating action or trigger event to the triggered action Figure 15 1 UPDATE item_numb quantity total_price XCXCXC XCXCXC XCXCXCX EXECUTE PROCEDURE XCXCXC XCXC XCXC u pd_it ems XCXCX XCXC XCXCXCXC XCXCXCXC XCXCX XCXC trigger even
246. ate and time The word USER for your user name The word DBSERVERNAME or SITENAME for the name of the computer where the database server is running Some columns of a table might not allow null values If you attempt to insert NULL in such a column the statement is rejected Or a column in the table may not permit duplicate values If you specify a value that is a duplicate of Modifying Data 4 7 Statements That Modify Data 4 8 Modifying Data one already in such a column the statement is rejected Some columns may even restrict the possible column values allowed These restrictions are placed on columns using data integrity constraints For more information on data restrictions see the section Database Privileges on page 4 15 Only one column in a table can have the SERIAL data type The database server generates values for a serial column To make this happen when you insert values specify the value zero for the serial column The database server generates the next actual value in sequence Serial columns do not allow null values You can specify a nonzero value for a serial column as long as it does not duplicate any existing value in that column and the database server uses the value However that nonzero value may set a new starting point for values that the database server generates The next value the database server gener ates for you is one greater than the maximum value in the column Do not specify the
247. ated dbspace always receives new extents that are adjacent to its old extents The size of these extents is not important because being adjacent they perform like one large extent When you assign an extent size to these kinds of tables the only consideration is to avoid creating large numbers of extents A large number of extents causes the database server to spend a small amount of extra time on bookkeeping In addition an upper limit exists on the number of extents allowed This is covered in the section Upper Limit on Extents on page 10 10 Next extent sizes become important when two or more large and growing tables share a dbspace Because the extents added to the different tables are interleaved each new extent represents another long seek that must be made when reading sequentially It also extends the total distance over which the disk arm must range when reading nonsequentially No upper limit exists on extent sizes except the size of the dbspace When you know the final size of a table or can confidently predict it within 25 percent allocate all its space in the initial extent When tables grow steadily to unknown size assign them next extent sizes that let them share the dbspace with a small number of extents each The following list contains one possible approach Decide on the ratio in which the dbspace is shared among the tables For example you might divide the dbspace among three tables in the ratio 0 4 0 2
248. atement You hide complexities of a multitable join in the view so that neither users nor application programmers need to repeat them Creating Views Th e following example creates a view based on a table in the stores6 database CRI EATE VIEW name_only AS SELECT customer_num fname lname FROM customer Th e view exposes only three columns of the table Because it contains no WHERE clause the view does not restrict the rows that can appear Th e following example creates a view based on a table that is available when NLS has been enabled In it the view column and table names contain foreign characters CRI FATE VIEW ca_va AS SELECT num ro nom FROM abonn s 11 20 Granting and Limiting Access to Your Database Using Views The following example is based on the join of two tables CREATE VIEW full_addr AS SELECT addressl address2 city state sname zipcode FROM customer state WHERE customer state state code The table of state names reduces the redundancy of the database it allows for storing the full state names only once which can be very useful for lengthy state names such as Minnesota This full_addr view lets users retrieve the address as if the full state name were stored in every row The following two queries are equivalent n Lee E LECT FROM full_addr WHERE customer_num 105 SELECT addressl address2 city state sname zipcod
249. atement are shown in Chapter 1 of the Informix Guide to SQL Syntax Some Basic Concepts The SELECT statement unlike INSERT UPDATE and DELETE statements does not modify the data in a database It is used simply to query on the data Whereas only one user at a time can modify data multiple users can query on or select the data concurrently The statements that modify data are dis cussed in Chapter 4 Modifying Data The INSERT UPDATE and DELETE statements appear in Chapter 1 of the Informix Guide to SQL Syntax 2 4 Composing Simple SELECT Statements Privileges Introducing the SELECT Statement In a relational database a column is a data element that contains a particular type of information that occurs in every row in the table A row is a group of related items of information about a single entity across all columns in a database table You can select columns and rows from a database table from a system catalog table a file that contains information on the database or from a view which is a virtual table created to contain a customized set of data System catalog tables are shown in Chapter 2 of the Informix Guide to SQL Reference Views are discussed in Chapter 1 of the Informix Guide to SQL Syntax Before you can query on data you must have the Connect privilege to the database and the Select privilege to the tables in it These privileges normally are granted to all users as a matter of course Database access
250. ater flexibility of the PRINT statement Select each compo nent of a DATETIME or INTERVAL value as an expression using EXTEND Give each expression an alias for convenience SELECT EXTEND START_TIME HOUR TO HOUR H EXTEND START_TIME MINUTE TO MINUTE M Then in the report combine the components in a PRINT expression with the desired punctuation PRINT Start work at H USING amp amp M USING amp amp hours Start work at 0800 hours The second parameter r is an optional reserve length that sets a lower limit on the length of an item as stored on disk When an item is shorter than 1 r bytes are nevertheless allocated to hold it The purpose is to save time when rows are updated See Variable Length Execution Time on page 9 17 9 16 Implementing Your Data Model Defining the Domains The advantages of the VARCHAR m r or NVARCHAR m r data type over the CHAR n or NCHAR m r type are found in the following list e It conserves disk space when the lengths of data items vary widely or when only a few items are longer than average Queries on the more compact tables can be faster The following list describes its disadvantages It does not allow lengths that exceed 255 characters Updates of a table can be slower in some circumstances It is not available with all Informix database servers Variable Length Execution Time When the VARCHAR m r o
251. ation on external tables and external databases see Chapter 12 Understanding Informix Networking in this manual and Chapter 1 in the Informix Guide to SQL Syntax You also can use synonyms as shorthand references to the long names of exter nal and current tables and views For details on how to create and use syn onyms see Chapter 12 Understanding Informix Networking in this manual and the CREATE SYNONYM statement in Chapter 1 of the Informix Guide to SQL Syntax Composing Simple SELECT Statements Multiple Table SELECT Statements The INTO TEMP Clause By adding an INTO TEMP clause to your SELECT statement you can temporarily save the results of a multiple table query in a separate table that can be queried or manipulated without modifying the database Temporary tables are dropped when you end your SQL session or when your program or report terminates Query 2 80 creates a temporary table called stockman and stores the results of the query in it Because all columns in a temp table must have names the alias adj_price is required SELECT DISTINCT stock_num manu_name description unit_price unit_price 1 05 adj_price FROM stock manufact WHERE manufact manu_code stock manu_code INTO TEMP stockman Query 2 80 stock_num manu_name description unit_price adj_price 1 Hero baseball gloves 250 00 262 5000 1 Husky baseball gloves 800 00 840 0000 1 Smith baseball gloves 450 00 472 5000 2 He
252. ble You must always use a correlation name with a column name in SQL statements within a FOR EACH ROW triggered action unless the statement is valid independent of the trig gered action See CREATE TRIGGER in Chapter 1 of the Informix Guide to SQL Syntax Using the WHEN Condition As an option you can precede a triggered action with a WHEN clause to make the action dependent on the outcome of a test The WHEN clause consists of the keyword WHEN followed by the condition statement given in parenthe ses In the CREATE TRIGGER statement the WHEN clause follows the key words BEFORE AFTER or FOR EACH ROW and precedes the triggered action list When a WHEN condition is present if it evaluates to true the triggered actions execute in the order in which they appear If the WHEN condition evaluates to false or unknown the actions in the triggered action list do not execute If the trigger specifies FOR EACH ROW the condition is evaluated for each row also In the following trigger example the triggered action executes only if the condition in the WHEN clause is true that is if the post update unit price is greater than two times the pre update unit price CREATE TRIGGER up_price UPDATE OF unit_price ON stock REFERENCING OLD AS pre NEW AS post FOR EACH ROW WHEN post unit_price gt pre_unit_price 2 INSERT INTO warn_tab VALUES pre stock_num pre order_num pre unit_price post unit_price CURRENT
253. ble 9 28T 10 12T options bad row limits 5 23R batch size 5 22R command file syntax check 5 21R load start point 5 22R specifying field delimiter with DBDELIMITER 4 18R writing a command file in character position form 5 31R writing a command file in delimiter form 5 26R DBMONEY environment variable 4 20R 9 12T DBMS See Database management system DBNLS environment variable 1 16R 4 48R DBPATH environment variable 4 21R 1 1415 1 4235 12 14T DBPRINT environment variable 4 24R DBREMOTECMD environment variable 4 25R Directory extension dbs extension 1 101S dbs extension Intro 11R 1 585 1 141S Index 13 14 Index dbschema utility create schema for a database 5 34R description of 5 33R options obtaining privilege schema 5 36R obtaining synonym schema 5 35R specifying a table view or procedure 5 37R owner conventions 5 35R use of 9 26T DBSERVERNAME function returning servername 1 4385 use in ALTER TABLE 1 185 in CREATE TABLE 1 888 in expression 1 438S in SELECT 2 63T 2 65T 3 20T dbspace definition of 10 4T division into extents 10 8T for temporary tables 10 6T mirrored 10 5T multiple access arms in 10 7T on dedicated device 10 6T relation to tblspace 10 7T root 10 5T selecting with CREATE DATABASE 1 57S 9 22T DBSPACETEMFP environment variable 4 26R 1 100S DBTEMP environment variable 4 27R DBTIME environment variable 4 27R DBUPSPACE environment variable 4 30R DDL statements summary 1 5S Deadlock de
254. blems arise you do not need to read this section again Programming for a Multiuser Environment 7 15 Locking with Other Database Servers Locking with Other Database Servers INFORMIX OnLine Dynamic Server manages its own locking so that it can provide the different kinds of locks and levels of isolation described in the preceding topics Other Informix database servers implement locks using the facilities of the host operating system and cannot provide the same conveniences Some host operating systems provide locking functions as operating system services In these systems database servers support the SET LOCK MODE statement Some host operating systems do not provide kernel locking facilities In these systems the database server performs its own locking based on small files that it creates in the database directory These files have the suffix lok You can tell the kind of system in which your database server is running by executing the SET LOCK MODE statement and testing the error code as shown in the following fragment of INFORMIX ESQL C code define LOCK_ONLINE 1 define LOCK_KERNEL 2 define LOCK_FILES 3 int which_locks int locktype locktype LOCK_FILES exec sql set lock mode to wait 30 if sqlca sqlcode 0 locktype LOCK_ONLINE else exec sql set lock mode to wait if sqlca sqlcode locktype LOCK_KERNEL restore default condition exec sql set lock mode
255. blems before executing the procedure To obtain the listing of compile time warnings for your procedure use the WITH LISTING IN clause in your CREATE PROCEDURE statement as shown in the following example CREATE PROCEDURE read_address lastname CHAR 15 one argument RETURNING CHAR 15 CHAR 15 CHAR 20 CHAR 15 CHAR 2 CHAR 5 6 items WITH LISTING IN acctng test listfile compile time warnings go here end of the procedure read_address If you are working on a network the listing file is created on the machine where the database resides If you provide an absolute pathname and file name for the file the file is created where you specify If you provide a relative pathname for the listing file the file is created in your home directory on the machine where the database resides If you do not have a home directory the file is created in the root directory After you create the procedure you can view the file specified in the WITH LISTING IN clause to see the warnings it contains Generating the Text or Documentation Once you create the procedure it is stored in the sysprocbody system catalog table The sysprocbody system catalog table contains the executable proce dure as well as the text of the original CREATE PROCEDURE statement and the documentation text 14 8 Creating and Using Stored Procedures Creating and Using Stored Procedures Looking at the Procedure Text To generate the text of t
256. can join the dominant table to either subservient table with out affecting the results if the dominant table and the subservient table share a common column Composing Advanced SELECT Statements 3 29 Creating Advanced Joins Outer Join of Two Tables to a Third Table Query 3 25 shows an outer join that is the result of an outer join of each of two tables to a third table In this fourth type of outer join join relationships are possible only between the dominant table and the subservient tables SELECT c customer_num lname o order_num order_date call_dtime FROM customer c OUTER orders o OUTER cust_calls x WHERE c customer_num o customer_num AND c customer_num x customer_num ORDER BY lname INTO TEMP service Query 3 25 3 30 Composing Advanced SELECT Statements Creating Advanced Joins Query 3 25 individually joins the subservient tables orders and cust_calls to the dominant customer table it does not join the two subservient tables An INTO TEMP clause selects the results into a temporary table for further manipulation or queries as shown in Query Result 3 25 customer_num lname order_num order_date call_dtime 14 Albertson 18 Baxter 13 Beatty 03 Currie 15 Grant 010 06 17 1993 23 Hanlon 020 07 11 1993 25 Henry 04 Higgins 003 05 22 1993 04 Higgins 001 05 20 1993 04 Higgins 013 06 22 1993 04 Higgins 011 06 18 1993 0 Jaeger 015 06 27 1993 1993 07 07 10 24 0 Jaeger 008 06 07 1993 1993 07
257. card at the end of a string to retrieve all the rows where the description begins with the characters bicycle SELECT FROM stock WHERE description LIKE bicycle ORDER BY description manu_code SELECT FROM stock WHERE description MATCHES bicycle ORDER BY description manu_code Query 2 32 Either statement returns the rows found in Query Result 2 32 stock_num manu_code description unit_price unit unit_descr 102 PRC bicycle brakes 480 00 case 4 sets case 102 SHM bicycle brakes 220 00 case 4 sets case 114 PRC bicycle gloves 120 00 case 10 pairs case 107 PRC bicycle saddle 70 00 pair pair 106 PRC bicycle stem 23 00 each each 101 PRC bicycle tires 88 00 box 4 box 101 SHM bicycle tires 68 00 box 4 box 105 PRC bicycle wheels 53 00 pair pair 105 SHM bicycle wheels 80 00 pair pair Query Result 2 32 The comparison bicycle3 or bicycle specifies the characters bicycle followed by any sequence of zero or more characters It matches bicycle stem with stem matched by the wildcard It matches to the characters bicycle alone if a row exists with that description Query 2 33 narrows the search by adding another comparison condition that excludes a manu_code of PRC SELECT FROM stock WHERE description LIKE bicycle AND manu_code NOT LIKE PRC ORDER BY description manu_code Query 2 33 Composing Simple SELECT Statements 2 41 Single Table SELECT Statements The statement retrieves on
258. cation 29 Summary 29 4 2 Modifying Data Chapter Overview Modifying data is fundamentally different from querying data Querying data involves examining the contents of tables Modifying data involves changing the contents of tables Think about what happens if the system hardware or software fails during a query In this case the effect on the application can be severe but the database itself is unharmed However if the system fails while a modification is under way the state of the database is in doubt Obviously this can have far reach ing implications Before you delete insert or update rows in a database ask yourself the following questions e Is user access to the database and its tables secure that is are specific users given limited database and table level privileges Does the modified data preserve the existing integrity of the database e Are systems in place that make the database relatively immune to external events that might cause system or hardware failures If you are unable to answer yes to each of these questions do not panic Solutions to all these problems are built in to the Informix database servers After an introduction to the statements that modify data this chapter dis cusses these solutions Chapters 8 through 11 talk about these topics in greater detail Statements That Modify Data The following three statements modify data DELETE INSERT UPDATE Although these SQL statement
259. caught it is passed out of this BEGIN END block to the block that con tains this block BEGIN ON EXCEPTION SET esql eisam trap all errors IF esql 206 THEN table not found recover somehow ELSE RAISE exception esql eisam pass the error up END IF END EXCEPTION do something END Simulating SQL Errors You can generate errors to simulate SOL errors as shown in the following example Here if the user is pault then the stored procedure acts as if that user has no update privileges even if he really does have that privilege BEGIN IF user pault THEN RAISE EXCEPTION 273 deny Paul update privilege END IF END Creating and Using Stored Procedures 14 31 Exception Handling 14 32 Using RAISE EXCEPTION to Exit Nested Code Figure 14 16 You can use the RAISE EXCEPTION statement to break out of a deeply nested block as shown in Figure 14 16 If the innermost condition is true if aa is negative then the exception is raised and execution jumps to the code fol lowing the END of the block In this case execution jumps to the TRACE statement BEGIN ON EXCEPTION IN 1 END EXCEPTION WITH RESUME do nothing significant cont BEGIN FOR i IN 1 TO 1000 FOREACH select INTO aa FROM t IF aa lt 0 THE RAISE EXCEPTION 1 emergency exit END IF END FOREACH END FOR RETURN 1 END do something emergency exit to this statement TRACE Ne
260. ccess or INFORMIX SQL menu options the program warns you and asks for confirmation However an unconditional delete from within a program can occur without warning Deleting a Known Number of Rows 4 4 Modifying Data The WHERE clause in a DELETE statement has the same form as the WHERE clause in a SELECT statement You can use it to designate exactly which row or rows should be deleted You can delete a customer with a specific customer number as shown in the following example DELETE FROM customer WHERE customer_num 175 In this example because the customer_num column has a unique constraint you are sure that no more than one row is deleted Statements That Modify Data Deleting an Unknown Number of Rows You can also choose rows based on nonindexed columns as shown in the fol lowing example DELETE FROM customer WHERE company Druid Cyclery Because the column tested does not have a unique constraint this statement might delete more than one row Druid Cyclery may have two stores both with the same name but different customer numbers You can find out how many rows might be affected by a DELETE statement by selecting the count of qualifying rows from the customer table for Druid Cyclery SELECT COUNT FROM customer WHERE company Druid Cyclery You can also select the rows and display them to be sure they are the ones you want to delete Using a SELECT statement as a test is
261. cedure Names and SQL Functions For information about ambiguities between procedure names and SQL function names see the Informix Guide to SQL Syntax SPL Expressions You can use any SQL expression in a stored procedure except for an aggregate expression The complete syntax and notes for SQL expressions are described in Chapter 1 of the Informix Guide to SQL Syntax The following examples contain SQL expressions varl varl var2 5 read_address Miller read_address lastname Miller get_duedate acct_num 10 UNITS DAY fname 1 5 lname 415 get_phonenum cust_name Assigning Values to Variables The following ways can assign a value to a procedure variable e Using a LET statement e Using a SELECT INTO statement e Using a CALL statement with a procedure that has a RETURNING clause e Using an EXECUTE PROCEDURE INTO statement Use the LET statement to assign a value to one or more variables The following example illustrates several forms of the LET statement LET a b a LET a b c d LET a b SELECT fname lname FROM customer WHERE customer_num 101 LET a b read_name 101 Creating and Using Stored Procedures 14 21 Program Flow Control Use the SELECT statement to assign a value directly from the database to a variable The statement in the following example accomplishes the same task as the third LET statement in the previous example SELECT fname lname into
262. cess See Disk access sequential Sequential cursor definition of 1 149S 5 23T use of 1 1495 with FETCH 1 195S SERIAL data type description of 3 19R 9 7T generated number in SQLERRD 5 12T in ALTER TABLE 1 175 in INSERT 1 2515 inserting a starting value 4 8T inserting values 3 19R resetting values 3 19R syntax 1 425S treatment by dbschema 5 34R with stored procedures 2 85 Server See Database server SET clause 1 125S 4 14T SET CONNECTION statement syntax and use 1 346S with concatenation operator 1 432S SET CONSTRAINTS statement syntax and use 1 349S use with CREATE TRIGGER 1 131S SET DEBUG FILE TO statement syntax and use 1 351S with TRACE 2 425 SET DESCRIPTOR statement syntax 1 353S the VALUE option 1 355S with concatenation operator 1 4325 X Open mode 1 3575 Set difference 3 53T SET EXPLAIN statement interpreting output 1 361S 13 29T MERGE JOIN information 1 362S optimizer access paths 1 361S output examples 1 362S SORT SCAN information 1 3625 syntax 1 360S writes query plan 13 12T Set intersection 3 51T SET ISOLATION statement controlling the effect of locks 4 28T default database levels 1 368S definition of isolation levels 1 367S effects of isolation 1 368S restrictions 7 9T syntax 1 366S SET keyword syntax in UPDATE 1 383S use in UPDATE 1 386S 4 12T Index 39 SET LOCK MODE statement controlling the effect of locks 4 28T description of 7 13T kernel locking 1 370S setting wait period 1 371S synta
263. changing it so that it performs the following actions e Reads fewer rows e Avoids a sort sorts fewer rows or sorts on a simpler key Reads rows sequentially instead of nonsequentially The way to achieve these ends is not always obvious The specific methods depend on the details of the application and the database design The follow ing paragraphs suggest a general approach followed by some techniques that apply in limited circumstances Optimizing Your Queries 13 27 Making Queries Faster Preparing a Test Environment First select a single query that is too slow Then set up an environment in which you can take predictable repeatable timings of that query Without this environment you can never be sure whether a change helps If you are using a multiuser system or a network so that system load varies widely from hour to hour you may need to perform your experiments at the same time each day to obtain repeatable results Preferably you should exe cute tests when the system load is consistently light so that you are truly measuring only your query If the query is embedded in a complicated program consider extracting the SELECT statement and executing it interactively or embedding it in a simpler program If the real query takes many minutes or hours to complete it may be a good idea to prepare a scaled down database in which you can run tests more quickly This can be helpful but you must be aware of the following po
264. ck board 84 00 case 12 case 311 SHM water gloves 48 00 box 4 pairs box 312 SHM racer goggles 96 00 box 12 box 312 HRO racer goggles 72 00 box 12 box 313 SHM swim cap 72 00 box 12 box 313 ANZ swim cap 60 00 box 12 box Query Result 3 34 Composing Advanced SELECT Statements 3 41 Set Operations Note that no logical limit exists to the number of subqueries a SELECT statement can have but the size of any statement is physically limited when considered as a character string However this limit is probably larger than any practical statement you are likely to compose Perhaps you want to check whether information has been entered correctly in the database One way to find errors in a database is to write a query that returns output only when errors exist A subquery of this type serves as a kind of audit query as shown in Query 3 35 SELECT FROM items WHERE total_price quantity SELECT unit_price FROM stock WHERE stock stock_num items stock_num AND stock manu_code items manu_code Query 3 35 Query Result 3 35 returns only those rows for which the total price of an item on an order is not equal to the stock unit price times the order quantity Assuming that no discount has been applied such rows must have been entered incorrectly in the database item_num order_num stock_num manu_code quantity total_price 1 1004 1 HRO 1 960 00 2 1006 5 NRG 5 190 00 Query Result 3 35 Query 3 35 returns rows only w
265. clause or try selecting a subset of rows into a temporary table and searching only them Avoiding Difficult Regular Expressions The MATCHES and LIKE keywords support wildcard matches technically known as regular expressions Some regular expressions are more difficult than others for the database server to process A wildcard in the initial position as in the following example find customers whose first names do not end in y forces the database server to examine every value in the column as shown in the following example SELECT FROM customer WHERE fname NOT LIKE y An index cannot be used with such a filter so the table in this example must be accessed sequentially If a difficult test for a regular expression is essential avoid combining it with a join If necessary process the single table applying the test for a regular expression to select the desired rows Save the result in a temporary table and join that table to the others Regular expression tests with wildcards in the middle or at the end of the operand do not prevent the use of an index when one exists 13 32 Optimizing Your Queries Making Queries Faster Avoiding Noninitial Substrings A filter based on a noninitial substring of a column also requires every value in the column to be tested as shown in the following example SELECT FROM customer WHERE zipcode 4 5 gt 50 An index cannot be used to evaluate such a filter
266. codes ISAM error codes To generate a listing of traced values first use the SQL statement SET DEBUG FILE to name the file that is to contain the traced output When you create your procedure include the TRACE statement in one of its forms Creating and Using Stored Procedures 14 11 Creating and Using Stored Procedures 14 12 Figure 14 7 The following ways specify the form of TRACE output TRACE ON traces all statements except SQL statements The contents of variables are printed before being used Procedure calls and returned values are also traced TRACE PROCEDURE traces only the procedure calls and returned values TRACE expression prints a literal or an expression If necessary the value of the expression is calculated before being sent to the file Figure 14 7 shows how you can use the TRACE statement with a version of the read_address procedure Several of the SPL statements shown in this example have not been discussed but the entire example demonstrates how the TRACE statement can help you monitor execution of the procedure CREATE PROCEDURE read_many lastname CHAR 15 RETURNING CHAR 15 CHAR 15 CHAR 20 CHAR 15 CHAR 2 CHAR 5 DEFINE p_lname p_fname p_city CHAR 15 DEFINE p_add CHAR 20 DEFINE p_state CHAR 2 DEFINE p_zip CHAR 5 DEFINE lcount i INT LET lcount 1 TRACE ON Every expression will be traced from here on TRACE Foreach starts A trace statement with a
267. come larger and the response time begins to degrade you must turn to practical solutions The first step is to understand and take advantage of the tools that INFORMIX OnLine Dynamic Server offers It permits you to arrange your tables on the hardware for maximum benefit Then one step at a time and always measuring you can begin complicating the structure of the data model and the programs that use it 10 36 Tuning Your Data Model Chapter Granting and Limiting Access to Your Database Chapter Overview 3 Controlling Access to Databases 4 Securing Database Files 4 Multiuser Systems 4 Single User Systems 4 Securing Confidential Data 5 Granting Privileges 5 Database Level Privileges 5 Connect Privilege 6 The Users and the Public 6 Resource Privilege 7 Database Administrator Privilege 7 Ownership Rights 7 Table Level Privileges 7 Access Privileges 8 Index Alter and References Privileges 8 Privileges in the System Catalog 9 Column Level Privileges 10 Procedure Level Privileges 12 Automating Privileges 13 Automating with INFORMIX 4GL 13 Automating with a Command Script 14 Controlling Access to Data Using Stored Procedures 15 Restricting Reads of Data 16 Restricting Changes to Data 16 Monitoring Changes to Data 17 Restricting Object Creation 18 Using Views 19 Creating Views 20 Duplicate Rows from Views 22 Restrictions on Views 22 When the Basis Changes 22 Modifying Through a View 23 Deleting Through a View
268. could execute a statement such as the following one GRANT UPDATE emp_key emp_name hire_date dept_num ON hr_data TO marvin_t This statement gives certain users the ability to maintain the nonsensitive columns but denies them authorization to change performance ratings or sal aries The person in the MIS department who assigns computer user ids is the beneficiary of a statement such as the following one GRANT UPDATE user_id ON hr_data TO eudora_b Granting and Limiting Access to Your Database 11 11 Granting Privileges On behalf of all users who are allowed to connect to the database but who are not authorized to see salaries or performance reviews you execute statements such as the following one to permit them to see the nonsensitive data GRANT SELECT emp_key emp_name hire_date dept_num user id ON hr_data TO george_b john_s These users can perform queries such as the following one SELECT COUNT FROM hr_data WHERE dept_num IN 32 33 34 However any attempt to execute a query such as the following one produces an error message and no data SELECT performance_level FROM hr_data WHERE emp_name LIKE Smythe Procedure Level Privileges You can apply the Execute privilege on a procedure to authorize nonowners to run a procedure If you create a procedure in a database that is not ANSI compliant the default procedure level privilege is Public you do not need to grant the E
269. ction can be written for another database this one uses familiar column names The function declares scan_ord a cursor to scan all rows in the orders table It is declared with the FOR UPDATE clause which states that the cursor can modify data If the cursor opens properly the function begins a transaction and then loops over rows of the table For each row it uses an embedded SELECT statement to determine how many rows of the table have the order number of the current row This step fails without the correct isolation level as described in Chapter 7 Programming for a Multiuser Environment In the demonstration database with its unique index on this table the count returned to dup_cnt is always 1 However if it is greater the function deletes the current row of the table reducing the count of duplicates by one Clean up functions of this sort are sometimes needed but they generally need more sophisticated design This one deletes all duplicate rows except the last one delivered by the database server That ordering has nothing to do with the contents of the rows or their meanings You can improve the func tion in Figure 6 2 by adding perhaps an ORDER BY clause to the cursor dec laration However you cannot use ORDER BY and FOR UPDATE together A better approach is sketched later in An Insert Example on page 6 12 Using INSERT You can embed the INSERT statement in programs Its form and use ina program are the same
270. cture lt BYTE value gt cat_advert Ultimate in Puncture Protection Tires Designed for In City Riding description bicycle tires unit_price 88 00 unit box unit_descr 4 box Query Result 2 75 Note that Query Result 2 75 includes a TEXT column cat_descr a BYTE column cat_picture and a VARCHAR column cat_advert Multiple Table Join A multiple table join connects more than two tables on one or more associ ated columns it can be an equi join or a natural join Composing Simple SELECT Statements 2 77 Multiple Table SELECT Statements Query 2 76 creates an equi join on the catalog stock and manufact tables and retrieves the following row SELECT FROM catalog stock manufact WHERE catalog stock_num stock stock_num AND stock manu_code manufact manu_code AND catalog_num 10025 Query 2 76 Query Result 2 76 retrieves the rows shown in Query 2 76 catalog_num 0025 stock_num 06 manu_code PRC cat_descr Hard anodized alloy with pearl finish 6mm hex bolt hardware Available in lengths of 90 140mm in 10mm increments cat_picture lt BYTE value gt cat_advert ProCycle Stem with Pearl Finish stock_num 06 manu_code PRC description bicycle stem unit_price 23 00 unit each unit_descr each manu_code PRC manu_name ProCycle lead_time 9 Query Result 2 76 Note that the manu_code is repeated three times once for each table and stock_num is repeated twice Because of the considerable du
271. currency symbols for columns that contain money values Just specify the numeric value of the amount The database server can convert between numeric and character data types You can give a string of numeric characters for example 0075 6 as the value of a numeric column The database server converts the numeric string to a number An error occurs only if the string does not represent a number You can specify a number or a date as the value for a character column The database server converts that value to a character string For example if you specify TODAY as the value for a character column a character string repre senting today s date is used The format used is specified by the DBDATE environment variable Listing Specific Column Names You do not have to specify values for every column Instead you can list the column names after the table name and then supply values for only those col umns you named The following example shows a statement that inserts a new row into the stock table INSERT INTO stock stock_num description unit_price manu_code VALUES 115 tyre pump 114 SHM Statements That Modify Data Notice that only the data for the stock number description unit price and manufacturer code is provided The database server supplies the following values for the remaining columns enerates a serial number for an unlisted serial column e Jt t 1 ber fi listed 1 col e It generates a defaul
272. cursor The code in Figure 6 4 calls next_cust repeatedly When it returns non null data the PUT statement sends the returned data to the row buffer When the buffer fills the rows it contains are automatically sent to the database server The loop normally ends when next_cust has no more data to return Then the FLUSH statement writes any rows that remain in the buffer after which the transaction terminates Examine the INSERT statement in Figure 6 3 once more The statement by itself not part of a cursor definition inserts a single row into the customer table In fact the whole apparatus of the insert cursor can be dropped from the example code and the INSERT statement can be written into Figure 6 4 where the PUT statement now stands The difference is that an insert cursor causes a program to run somewhat faster 6 10 Modifying Data Through SQL Programs Using INSERT Status Codes After PUT and FLUSH When a program executes a PUT statement the program should test whether the row is placed in the buffer successfully If the new row fits in the buffer the only action of PUT is to copy the row to the buffer No errors can occur in this case However if the row does not fit the entire buffer load is passed to the database server for insertion and an error can occur The values returned into the SQL Communications Area give the program the information it needs to sort out each case SOLCODE is set after every PUT statement to z
273. cust_calls Query 3 18 username rowid zenda 257 zenda 258 zenda 259 zenda S13 zenda 514 zenda 515 zenda 769 Query Result 3 18 You also can use the USER function in a WHERE clause when you select the rowid Composing Advanced SELECT Statements 3 19 Creating Advanced Joins Query 3 19 returns the rowid for only those rows inserted or updated by the user who performs the query SELECT rowid FROM cust_calls WHERE user_id USER Query 3 19 For example if the user riche used Query 3 19 the output would be as shown in Query Result 3 19 rowid 258 259 Query Result 3 19 Using the DBSERVERNAME Function With INFORMIX OnLine Dynamic Server you can add the DBSERVERNAME keyword or its synonym SITENAME to a query to find out where the current database resides Query 3 20 finds the database server name and the user name as well as the rowid and the tabid which is the serial interval table identifier for system catalog tables SELECT DBSERVERNAME server tabid rowid USER username FROM systables WHERE tabid gt 105 OR rowid lt 260 ORDER BY rowid Query 3 20 3 20 Composing Advanced SELECT Statements Creating Advanced Joins Query 3 20 assigns display labels to the DBSERVERNAME and USER expressions and returns the 10 rows from the systables system catalog table as shown in Query Result 3 20 server tabid rowid username manatee 1 257 zenda manatee 2 258 zenda manatee 3 259 ze
274. customer Query 2 69 Composing Simple SELECT Statements 2 67 Single Table SELECT Statements The output from this stored procedure query is shown in Query Result 2 69 customer_num lname n_orders L01 Pauli L02 Sadler L03 Currie L04 Higgins LO5 Vector L06 Watson LO7 Ream 108 Quinn 109 iller L10 Jaeger L11 Keyes 112 Lawson 113 Beatty 114 Albertson ETS Grant 116 Parmelee L17 Sipes 118 Baxter L19 Shorter L20 Jewell L21 Wallack L22 O Brian L23 Hanlon L24 Putnum L25 Henry 126 Neelie 127 Satifer 128 Lessor OrRPrFPORPRFRPRRRFRFRFRFONFRFOOFEFNDTAONOHOOF Query Result 2 69 You can use stored procedures to encapsulate operations that you frequently perform in your queries For example the condition in Query 2 70 contains a procedure conv_price that converts the unit price of a stock item to a different currency and adds any import tariffs SELECT stock_num manu_code description FROM stock WHERE conv_price unit_price ex_rate 1 50 tarif 50 00 lt 1000 Query 2 70 2 68 Composing Simple SELECT Statements Multiple Table SELECT Statements Multiple Table SELECT Statements You can select data from two or more tables by naming these tables in the FROM clause Add a WHERE clause to create a join condition between at least one related column in each table This creates a temporary composite table in which each pair of rows that satisfies the join condition is linked to form a si
275. d all of the statement blocks that follow the ON EXCEPTION statement It is not valid in the statement block that contains the ON EXCEPTION statement The pseudocode in Figure 14 15 shows where the exception is valid within the procedure That is if error 201 occurs in any of the indicated blocks the action labeled a201 occurs Creating and Using Stored Procedures 14 29 Exception Handling CREATE PROCEDURE scope DEFINE i INT BEGIN begin statement block A EXCEPTION IN 201 do action a201 D EXCEPTION EGIN statement block aa do action a201 valid here DWH lo D EGIN statement block bb do action a201 valid here W EI D ILE i lt 10 do something a201 is valid here D WHILE H I GI we ial Qu H zZ begin statement block B do something a201 is NOT valid here END END PROCEDURE Figure 14 15 Pseudocode showing the ON EXCEPTION statement is valid within a procedure User Generated Exceptions You can generate your own error using the RAISE EXCEPTION statement as shown in the following pseudocode example In this example the ON EXCEPTION statement uses two variables esql and eisam to hold the error numbers returned by the database server If an error occurs and the SQL error 14 30 Creating and Using Stored Procedures Exception Handling number is 206 the action defined in the IF clause is taken If any other SQL error is
276. d outside the model These are user assigned keys Sometimes more than one column or group of columns can be used as the primary key All columns or groups that qualify to be primary keys are called candidate keys All candidate keys are worth noting because their property of uniqueness makes them predictable in a SELECT operation When you select the columns of a candidate key you know the result can contain no duplicate rows Sometimes that allows you to predict the uniqueness of the rows returned It always means that the result of a SELECT operation can be a table in its own right with the selected candidate key as its primary key Composite Keys Some entities lack features that are reliably unique Different people can have identical names different books can have identical titles You can usually find a composite of attributes that work as a primary key For example it is rare for people to have identical names and identical addresses or for different books to have identical titles authors and publication dates Building Your Data Model 8 23 Translating E R Data Objects Into Relational Constructs System Assigned Keys A system assigned primary key is usually preferable to a composite key A system assigned key is a number or code that is attached to each instance of an entity when it is first entered into the database The easiest system assigned keys to implement are serial numbers because the database server can generate t
277. d throughout the book emphasizing the following topics What makes a database different from a collection of files What terms are used to describe the main components of a database What language is used to create query and modify a database What are the main parts of the software that manages a database and how do these parts work with each other Databases What and Why A database is a collection of information but so is a simple computer file What makes a database so special There must be reasons otherwise people would not spend so much money effort and computer time on databases Two fun damental differences exist First a database comprises not only data but also a plan or model of the data Second a database can be a common resource used concurrently by many people The Data Model The principal difference between information collected in a database and information in a file is in the way the data is organized A flat file is organized physically certain items precede or follow other items But the contents of a database are organized according to a data model A data model is a plan or map that defines the units of data and specifies how each unit is related to the others Introducing Database Features and SQL 1 3 Databases What and Why For example a number can appear in either a file or a database In a file it is simply a number that occurs at a certain point in the file A number in a data
278. del supports three fundamental oper ations two of which are illustrated in Figure 1 5 All three operations are defined in more detail with many examples in Chapter 2 Composing Sim ple SELECT Statements and Chapter 3 Composing Advanced SELECT Statements To select from a table is to choose certain rows leaving others aside One selection that could be made on the stock table is select all rows in which the manufacturer code is HRO and the unit price is between 100 00 and 200 00 To project from a table is to choose certain columns leaving others aside One projection that can be made from the stock table is show me the stock_num unit_descr and unit_price columns only A table contains information about only one entity when you want informa tion about multiple entities you must join their tables You can join tables in many ways The join operation is the subject of Chapter 3 Composing Advanced SELECT Statements stock Table stock num manu_code description unit_price unit unit_descr 1 HRO baseball gloves 250 00 case 10 gloves case 1 HSK baseball gloves 800 00 case 10 gloves case 1 SMT baseball gloves 450 00 case 10 gloves case 2 HRO baseball 126 00 case 24 case SELECTION 3 HSK baseball bat 240 00 case 12 case 4 HSK football 960 00 case 24 case 4 HRO football 480 00 case 24 case P O J E C T O N Figure 1 5 Illustration of selection and projection Introducing Database Features and
279. del were invented and developed at IBM in the early and middle 1970s Once IBM proved that it was possible to implement practical relational databases and that SQL was a usable language for manip ulating them other vendors began to provide similar products for non IBM computers For reasons of performance or competitive advantage or to take advantage of local hardware or software features each of these SQL implementations differed in small ways from each other and from the IBM version of the lan guage To ensure that the differences remained small a standards committee was formed in the early 1980s 1 14 Introducing Database Features and SQL Structured Query Language Committee X3H2 sponsored by the American National Standards Institute ANSI issued the SQL1 standard in 1986 This standard defines a core set of SQL features and the syntax of statements such as SELECT Informix SQL and ANSI SOL The SQL version that is supported by Informix products is highly compatible with standard SQL it is also compatible with the IBM version of the lan guage However it does contain extensions to the standard that is extra options or features for certain statements and looser rules for others Most of the differences occur in the statements that are not in everyday use For exam ple few differences occur in the SELECT statement which accounts for 90 percent of the SQL use for a typical person However the extensions do exist and t
280. der of the customer table is customer number order if a clustered index is on that column It is approximately that order if customer numbers are SERIAL values generated by the database server However if the physical order is random with respect to customer numbers each search of the index on orders might lead to a different page of index keys so that an index page is read for almost every row Note that when NLS is enabled indexes built on NCHAR or NVARCHAR columns are sorted using a country specific comparison value For example the Spanish double character Il may be treated as a single unique character instead of a pair of l s The Sort Merge Join Technique The sort merge table join provides a cost effective alternative to constructing a temporary index for a nested loop join It is considered by the optimizer only when the join is based on an equality filter and no index exists that can accomplish the join The sort merge join does not change the fundamental strategy of the optimizer Rather it provides a richer set of alternatives to nested loop joins using temporary indexes and alters the way the ORDER BY and GROUP BY paths are analyzed The path chosen by the optimizer is displayed in the out put when the SET EXPLAIN ON statement is issued as described in Chapter 1 of the Informix Guide to SQL Syntax and in Reading the Plan on page 13 12 of this manual Making Queries Faster In general you can speed up a query by
281. der_num 1009 AND orders order_num items order_num GROUP BY orders order_num orders order_date Although the join to the items table reads only three or four additional pages that might be too much time for an interactive program One solution is to add an order total column to the orders table 10 30 Tuning Your Data Model Denormalizing The costs of derived data are in disk space complexity and data integrity The disk space devoted to an order total column is wasted because the same information is stored twice Also the presence of the column makes the rows of the table wider fewer of them occur in a page and querying the table becomes slower Most important any program that updates the base attributes must be changed to also update the derived column Inevitably times occur when the derived column is wrong when it does not contain the right derived value Derived data is not reliable data In the example of a derived order price the unreliability occurs while an order is being entered When rows are added to the items table times occur when the order total in orders is not equal to the sum of the corresponding rows from items In general before you allow derived data to appear in the database you must define its accuracy as care fully as possible actually you should define as closely as possible the conditions under which the derived column is unreliable Adding Redundant Data A correct data model avoids re
282. derstand the details of these statements are best understood after a discussion on the use of cur sors from within programs Cursors are covered in Chapter 5 Programming with SQL and Chapter 6 Modifying Data Through SQL Programs Also see Chapter 7 Programming for a Multiuser Environment for more information about locking Data Replication 4 28 Modifying Data Data replication in the broadest sense of the term is when database objects have more than one representation at more than one distinct site For exam ple a database that is copied to a database server on a different machine so that reports can be run against the data without disturbing client applications using the original database is one way data can be replicated The following list describes the advantages of data replication Clients accessing replicated data locally as opposed to remote data that is not replicated experience improved performance because they do not have to use network services e Clients at all sites experience improved availability with replicated data because if local replicated data is unavailable a copy of the data is still available albeit remotely These advantages do not come without a cost Data replication obviously requires more storage for replicated data than for unreplicated data and updating replicated data can take more processing time than updating a single object Data replication can actually be im
283. disk operations during a query However costs are associated with indexes Space Costs of Indexes The first cost of an index is disk space An estimating method is given in Estimating Index Pages on page 10 16 Loosely an index contains a copy of every unique data value in the indexed columns plus a 4 byte pointer for every row in the table This information can add many pages to the table space requirements it is easy to have as many index pages as row pages Time Costs of Indexes The second cost of an index is time while the table is modified The descriptions that follow assume that approximately two pages must be read to locate an index entry That is the case when the index consists of a root page one intermediate level and leaf pages and the root page is already in a buffer The index for a very large table has two intermediate levels so roughly three pages are read when an entry is looked up Presumably one index has been used to locate the row being altered Its index pages are found in the page buffers However the pages for any other indexes that need altering must be read from disk Under these assumptions index maintenance adds time to different kinds of modifications as shown in the following list e When you delete a row from a table its entries must be deleted from all indexes The entry for the deleted row must be looked up two or three pages in and the leaf page must be rewritten one page out for a
284. display database data Chapter 3 Composing Advanced SELECT Statements discusses making advanced queries to retrieve and display database data Chapter 4 Modifying Data describes the statements you use to insert delete or update data and introduces the concepts of database privileges maintaining data integrity and archiving data Chapter 5 Programming with SQL discusses calling the database server retrieving rows and embedding data Chapter 6 Modifying Data Through SQL Programs provides an in depth look at INSERT DELETE and UPDATE statements and using these statements in SQL programs Chapter 7 Programming for a Multiuser Environment provides a complete discussion on concurrency isolation levels and locking Part II Designing and Managing Databases This part contains overview chapters about designing and managing databases Read these chapters to understand the entity relationship data model for databases and how to create and tune a database Chapter 8 Building Your Data Model describes the components of a data model and provides a step by step procedure for building one Chapter 9 Implementing Your Data Model tells you how to define database data types and create a database Chapter 10 Tuning Your Data Model discusses many of the details that help you set up an efficient database model including disk storage cal culating table sizes managing
285. dundancy by keeping any attribute only in the table for the entity it describes If the attribute data is needed in a different context you make the connection by joining tables But joining takes time If a frequently used join affects performance you can eliminate it by duplicating the joined data in another table In the demonstration database the manufact table contains the names of manufacturers and their delivery times In a real database it would contain many other attributes of a supplier such as address sale representative name and so on The contents of manufact are primarily a supplement to the stock table Suppose that a time critical application frequently refers to the delivery lead time of a particular product but to no other column of manufact For each such reference the database server must read two or three pages of data to perform the lookup You can add anew column lead_time to the stock table and fill it with copies of the lead_time column from the corresponding rows of manufact That eliminates the lookup which speeds up the application As with derived data redundant data takes space and poses an integrity risk In the example there is not one extra copy of each manufacturer s lead time there are many Each manufacturer can appear in stock many times The programs that insert or update a row of manufact must be changed to update multiple rows of stock as well Tuning Your Data Model 10 31 Maximizin
286. e FROM customer state WHERE customer state state code AND customer_num 105 However be careful when you define views that are based on joins Such views are not modifiable that is you cannot use them with UPDATE DELETE or INSERT statements Modifying through views is covered beginning on page 11 23 The following example restricts the rows that can be seen in the view CREATE VIEW no_cal_cust AS SELECT FROM customer WHERE NOT state CA This view exposes all columns of the customer table but only certain rows The following example is a view that restricts users to rows that are relevant to them CREATE VIEW my_calls AS SELECT FROM cust_calls WHERE user_id USER All the columns of the cust_calls table are available but only in those rows that contain the user ids of the users who execute the query Granting and Limiting Access to Your Database 11 21 Using Views Duplicate Rows from Views It is possible for a view to produce duplicate rows even when the underlying table has only unique rows If the view SELECT statement can return duplicate rows the view itself can appear to contain duplicate rows You can prevent this problem in two ways One way is to specify DISTINCT in the select list in the view However that makes it impossible to modify through the view The alternative is to always select a column or group of columns that is constrained to be unique You can be sure only unique ro
287. e lead_time stock_num manu_code description unit_price unit unit_descr manu_name lead_time stock_num manu_code description unit_price unit unit_descr manu_name lead_time stock_num manu_code description unit_price unit unit_descr Query Result 2 74 Smith 3 1 SMT baseball gloves 450 00 case 10 gloves case Smith 3 5 SMT tennis 25 00 each each racquet Smith 3 6 SMT tennis 36 00 case 24 cans case ball Anza 5 5 ANZ tennis racquet 19 80 each each All joins are associative that is the order of the joining terms in the WHERE clause does not affect the meaning of the join 2 76 Composing Simple SELECT Statements Multiple Table SELECT Statements Both of the statements in Query 2 75 create the same natural join SELECT catalog description unit_price unit unit_descr FROM catalog stock WHERE catalog stock_num stock stock_num AND catalog manu_code stock manu_code AND catalog_num 10017 SELECT catalog description unit_price unit unit_descr FROM catalog stock WHERE catalog_num 10017 AND catalog manu_code stock manu_code AND catalog stock_num stock stock_num Query 2 75 Each statement retrieves the row shown in Query Result 2 75 catalog_num 10017 stock_num 101 manu_code PRC cat_descr Reinforced hand finished tubular Polyurethane belted Effective against punctures Mixed tread for super wear and road grip cat_pi
288. e manufacturer code No lock is placed Program B issues a DELETE statement for that row It succeeds Program B deletes all rows of stock that use manufacturer code HRO Programming for a Multiuser Environment 7 11 Setting the Isolation Level 4 Program B ends Program A not aware that its copy of the Hero row is now invalid inserts a new row of stock using the manufacturer code HRO 6 Program A ends At the end a row occurs in stock that has no matching manufacturer code in manufact Furthermore Program B apparently has a bug it did not delete the rows it was supposed to delete The use of the Cursor Stability isolation level prevents these effects It is possible to rearrange the preceding scenario so that it fails even with Cursor Stability All that is required is for Program B to operate on tables in the reverse sequence to Program A If Program B deletes from stock before it removes the row of manufact no degree of isolation can prevent an error Whenever this kind of error is possible it is essential that all programs involved use the same sequence of access Because Cursor Stability locks only one row at a time it restricts concurrency less than does a table lock or database lock Repeatable Read Isolation The Repeatable Read isolation level asks the database server to put a lock on every row the program examines and fetches The locks that are placed are shareable for an ordinary cursor and promotable fo
289. e Aluminum for High School and Collegia Athletes 10007 4 HSK Quality Pigskin with Joe Namath Signature 10008 4 HRO Highest Quality Football for High School and Collegiate Competitions Query Result 2 23 Note that although the catalog table includes a column with the BYTE data type that column is not included in this SELECT statement because the out put would show only the words lt BYTE value gt by the column name You can display TEXT and BYTE values by using the PROGRAM attribute when using forms in INFORMIX SQL or INFORMIX 4GL or by writing a 4GL or an SQL API to do so Composing Simple SELECT Statements Single Table SELECT Statements Excluding a Range of Rows In Query 2 24 by using the keywords NOT BETWEEN the condition excludes rows that have the character range 94000 through 94999 in the zipcode column as shown in Query Result 2 24 SELECT fname lname company city state FROM customer WHERE zipcode NOT BETWEEN 94000 AND 94999 ORDER BY state Query 2 24 fname iname company city state Fred Jewell Century Pro Shop Phoenix AZ Frank Lessor Phoenix University Phoenix AZ Eileen Neelie Neelie s Discount Sp Denver co Jason Wallack City Sports Wilmington DE Marvin Hanlon Bay Sports Jacksonville FL James Henry Total Fitness Sports Brighton MA Bob Shorter The Triathletes Club Cherry Hill NJ Cathy O Brian The Sporting Life Princeton NJ Kim Satifer Big Blue Bike Shop Blue Isla
290. e As part of an INSERT statement to produce new rows e As part of an UPDATE statement to update information The SELECT statement is the primary way to query on information in a database It is your key to retrieving data in a program report screen form or spreadsheet This chapter shows how you can use the SELECT statement to query on and retrieve data in a variety of ways from a relational database It discusses how to tailor your statements to select columns or rows of information from one or more tables how to include expressions and functions in SELECT state ments and how to create various join conditions between relational database tables This chapter introduces the basic methods for retrieving data from a relational database More complex uses of SELECT statements such as sub queries outer joins and unions are discussed in Chapter 3 of this manual The syntax and usage for the SELECT statement are described in detail in Chapter 1 of the Informix Guide to SQL Syntax Most of the examples in this chapter come from the nine tables in the stores6 demonstration database which is installed with the software for your Infor mix SQL API In the interest of brevity the examples may show only part of the data that is retrieved for each SELECT statement See Appendix A in the Informix Guide to SQL Reference for information on the structure and contents of the stores6 database For emphasis keywords are shown in uppercase letters in
291. e is added to the voice entity to distinguish car phones home phones and office phones A voice number can be associated with only one voice type Building Your Data Model 8 15 Diagramming Your Data Objects The hours a fax machine is attended is added to the fax entity Whether a modem supports 300 1 200 or 2 400 baud rates is added to the modem entity Listing Your Attributes For now simply list the attributes for the telephone directory example with the entities with which you think they belong Your list should look something like Figure 8 6 name address voice fax modem fname street vce_num fax_num mdm_num Iname city vce_type operfrom b300 bdate state opertill b1200 anniv zipcode b2400 email child1 child2 child3 Figure 8 6 Attributes for the telephone directory example About Entity Occurrences An additional data object that you need to know about is the entity occurrence Each row in a table represents a specific single occurrence of the entity For example if customer is an entity a customer table represents the idea of customer in it each row represents one specific customer such as Sue Smith Keep in mind that entities will become tables attributes will become columns and rows will become entity occurrences Diagramming Your Data Objects At this point you have already discovered and understood the entities and relationships in your database That is the
292. e is almost a sequential scan Clustering and reclustering take a lot of space and time You can avoid some clustering by building the table in the desired order in the first place The physical order of rows is their insertion order so if the table is initially loaded with ordered data no clustering is needed Denormalizing The entity relationship data model described in Chapter 8 Building Your Data Model produces tables that contain no redundant or derived data tables that are well structured by the tenets of relational theory Sometimes to meet extraordinary demands for high performance you might have to modify the data model in ways that are undesirable from a theoretical standpoint This section describes some modifications and their associated costs Shorter Rows for Faster Queries As a general principle tables with shorter rows yield better performance than ones with longer rows This is because disk I O is performed in pages not in rows The shorter the rows of a table the more rows occur on a page The more rows per page the fewer I O operations it takes to read the table sequentially and the more likely it is that a nonsequential access can be satisfied from a buffer The entity relationship data model put all the attributes of one entity into a single table for that entity For some entities this can produce rows of awk ward length You can shorten the rows As the rows get shorter query performance should i
293. e items table that is the values before and after the effect of the triggering statement The REFERENCING clause enables you to do this The REFERENCING clause lets you create two prefixes that you can combine with a column name one to reference the old value of the column and one to reference its new value These prefixes are called correlation names You can create one or both correlation names depending on your requirements You indicate which one you are creating with the keywords OLD and NEW The following REFERENCING clause creates the correlation names pre_upd and post_upd to refer to the old and new values in a row REFERENCING OLD AS pre_upd NEW AS post_upd The following triggered action creates a row in log_record when quantity is updated in a row of the items table The INSERT statement refers to the old values of the item_num and order_num columns and to both the old and new values of the quantity column FOR EACH ROW INSERT INTO log_record VALUES pre_upd item_num pre_upd order_num USER CURRENT pre_upd quantity post_upd quantity The correlation names defined in the REFERENCING clause apply to all rows affected by the triggering statement Creating and Using Triggers 15 9 Using Triggered Actions If you refer to a column name in the triggering table without using a correla tion name the database server makes no special effort to search for the col umn in the definition of the triggering ta
294. e name of the directory in which your Informix products are installed Set INFORMIXSERVER to the name of the default database server The name of the default database server must exist in the INFORMIXDIR etc sql hosts file For a full description of environment variables see Chapter 4 of the Informix Guide to SQL Reference For more information about sqlhosts see the INFORMIX OnLine Dynamic Server Administrator s Guide or INFORMIX SE Administrator s Guide 2 Create a new directory for the SQL command files Create the directory by entering mkdir dirname 3 Make the new directory the current directory by entering cd dirname 8 Introduction New Features in Informix Version 6 0 Products That Use SQL 4 Create the demonstration database and copy over the sample command files by entering the following command To create the database without logging enter dbaccessdemo6 dbname To create the demonstration database with logging enter dbaccessdemo6 log dbname If you are using INFORMIX OnLine Dynamic Server by default the data for the database is put into the root dbspace If you wish you can specify a dbspace for the demonstration database To create a demonstration database in a particular dbspace enter dbaccessdemo6 dbspacename If you are using INFORMIX SE a subdirectory called dbname dbs is created in your current directory and the database files associated with stores6 are placed there You will see both data
295. e new data as part of an SOL command to insert a row and passes this command to the database server for execution Several types of applications exist Some allow you to access the database interactively using SQL others present the stored data in different forms related to its use The Database Server The database server is the program that manages the contents of the database as they are stored on disk The database server knows how tables rows and columns are actually organized in physical computer storage The database server also interprets and executes all SQL commands 1 16 Introducing Database Features and SQL The Database Software Interactive SOL To carry out the examples in this book and to experiment with SOL and database design for yourself you need a program that lets you execute SQL statements interactively DB Access and INFORMIX SQL are two such pro grams They assist you in composing SQL statements then they pass your SQL to the database server for execution and display the results to you Alternatively you may use a Wingz spreadsheet on a workstation or personal computer Wingz with its optional DataLink extension can talk to a database server Using the Wingz language HyperScript you can write SQL state ments and have rows of data returned to your spreadsheet for display Reports and Forms After you perfect a query to return precisely the data in which you are inter ested you need to format the d
296. e of the business rules for the example shown in this chapter Later when you normalize your data model some of the entities may expand or become other data objects See Normalizing Your Data Model on page 8 29 for additional information Pruning Your List of Entities When the list of entities seems complete prune it by making sure that each one has the following qualities e Itis significant List only entities that are important to the users of the database and worth the trouble and expense of computer tabulation e It is generic List only types of things not individual instances For instance symphony might be an entity but Beethoven s Fifth would be an entity instance or entity occurrence It is fundamental List only entities that exist independently without needing something else to explain them Anything you could call a trait a feature or a description is not an entity For example a part number is a feature of the fundamental entity called part Also do not list things that you can derive from other entities for example avoid any sum average or other quantity that you can calculate in a SELECT expression e Itis unitary Be sure that each entity you name represents a single class that it cannot be broken down into subcategories each with its own features In plan ning the telephone directory model see The Telephone Directory Example on page 8 6 an apparently simple entity the telep
297. e programs have access to a database concurrently and when at least one of them can modify data all programs must allow for the possibility that another program can change the data even as they read it The database server provides a mechanism of locks and isolation levels that usually allow programs to run as if they were alone with the data Programming for a Multiuser Environment 7 19 Summary 7 20 Programming for a Multiuser Environment Section II Designing and Managing Databases Building Your Data Model Chapter Overview 3 Why Build a Data Model 3 Entity Relationship Data Model Overview 3 Identifying and Defining Your Principal Data Objects 4 Discovering Entities 4 Choosing Possible Entities 5 Pruning Your List of Entities 5 The Telephone Directory Example 6 Diagramming Your Entities 8 Defining the Relationships 8 Connectivity 8 Existence Dependency 9 Cardinality 9 Discover the Relationships 10 Diagramming Your Relationships 14 Identifying Attributes 14 How to Identify an Attribute 15 Selecting Attributes for Your Entities 15 Listing Your Attributes 16 About Entity Occurrences 16 Diagramming Your Data Objects 16 How You Read Entity Relationship Diagrams 18 The Telephone Directory Example 18 What s Next 19 Translating E R Data Objects Into Relational Constructs 20 Rules for Defining Tables Rows and Columns 20 Placing Constraints on Columns 21 Determining Keys for Tables 22 Primary Keys 22 Forei
298. e temporary table in this form as shown in the following example SELECT FROM cust_with_balance WHERE postcode LIKE 98__ _ Each query reads the temporary table sequentially but the table has fewer rows than the primary table No nonsequential disk accesses are performed No sort is required because the physical order of the table is the desired order The total effort should be considerably less than before One possible disadvantage exists Any changes made to the primary table after the temporary table has been created are not reflected in the output This is not a problem for some applications but it may be for some Substituting Sorting for Nonsequential Access Nonsequential disk access is the slowest kind SQL hides this fact and makes it easy to write queries that access huge numbers of pages nonsequentially Sometimes you can improve a query by substituting the sorting ability of the database server for nonsequential access The following example demonstrates this and also demonstrates how to make numerical estimates of the cost of a query plan Imagine a large manufacturing firm whose database includes three tables shown in schematic form in Figure 13 6 Table diagrams in this form are described in Chapter 8 Building Your Data Model Not all the columns are shown The first table part contains the parts used in the products of the company Optimizing Your Queries 13 37 Making Queries Faster
299. eaf page to be read in addition to the page containing the row The number of pages read is approx imately r index height 1 where r is the number of rows to be looked up Although it is costly this kind of access is still a bargain because the alterna tive is to perform each look up by reading the entire orders table with disk costs proportional to r The other way the database server uses an index is to read it sequentially It does this to fetch the rows of a table in a specific order other than the physical order For this kind of access the database server reads the leaf pages in sequence treating them as a list of rows in key sequence Because the index pages are read only once the total of disk operations is proportional to r i i is the number of leaf pages in the index The Cost of Small Tables One conclusion you can draw from the preceding paragraphs is that small tables are never slow A table is small if it occupies so few pages that it can be retained entirely in the page buffers Any table that fits in four or fewer pages is certainly small in this sense In the stores6 database the state table that relates abbreviations to names of states has a total size less than 1 000 bytes it fits in at most two pages It can be included in any query at little cost No matter how it is used even if it is read sequentially many times it costs two disk accesses at most The Cost of NLS Functionality The sorting and i
300. easure ments such as The report runs in 2 hours 38 minutes or The average update takes 13 seconds but during peak hours it takes as long as 49 seconds Without numbers you cannot set meaningful goals When you have specific measurements you can obtain agreement on numeric goals for performance Without numbers you cannot measure and demonstrate your progress You need measurements to detect and demonstrate small improvements and to choose between alternative solutions Manual Timing You can obtain repeatable measurements with a hand operated stopwatch With practice most people can obtain timings that are repeatable within two tenths of a second Manual timing is useful if you are measuring only a few events that are at least several seconds long Very short events should be measured over several cycles of averaging to reduce the error in measurement Time from Operating System Commands Your operating system probably has a command that displays the time You can package an operation to be timed between two time commands in a command script Time from the Programming Language Most programming languages have a library function for the time of day If you have access to the source code you can insert statements to measure the time of specific actions For example if the application is written in 13 6 Optimizing Your Queries Optimizing Techniques INFORMIX 4GL you can use the CURRENT function to
301. eate the following view CREATE VIEW hr_public AS SELECT emp_key emp_name hire_date dept_num user_id FROM hr_data Users who are given the Select privilege for this view can see nonsensitive data and update nothing For the clerks in the Human Resources department who must enter new rows you create a different view as shown in the following example CREATE VIEW hr_enter AS SELECT emp_key emp_name hire_date dept_num FROM hr_data You grant these users both Select and Insert privileges on this view Because you the creator of both the table and the view have the Insert privilege on the table and the view you can grant the Insert privilege on the view to others who have no privileges on the table On behalf of the clerk in the MIS department who enters or updates new user ids you create still another view as shown in the following example CREATE VIEW hr_MIS AS SELECT emp_key emp_name user_id FROM hr_data This view differs from the previous view in that it does not expose the department number and date of hire Finally the managers need access to all columns and need the ability to update the performance review data for their own employees only These requirements can be met by creating a table hr_data that contains a department number and a computer user id for each employee Let it be a Granting and Limiting Access to Your Database 11 29 Summary rule that the managers are members of the dep
302. ecting Specific Columns The previous section showed how to select and order all data from a table However often all you want to see is the data in one or more specific col umns Again the formula is to use the SELECT and FROM clauses specify the columns and table and perhaps order the data in ascending or descending order with an ORDER BY clause If you want to find all the customer numbers in the orders table you would use a statement such as the one in Query 2 12 SELECT customer_num FROM orders Query 2 12 2 18 Composing Simple SELECT Statements Single Table SELECT Statements Query Result 2 12 shows how the statement simply selects all data in the customer_num column in the orders table and lists the customer numbers on all the orders including duplicates customer_num 101 104 104 104 104 106 106 1 a PRPRPPRPREPR NAY DUNF CO 19 120 121 122 123 124 126 127 Query Result 2 12 The output includes several duplicates because some customers have placed more than one order Sometimes you want to see duplicate rows in a projec tion At other times you want to see only the distinct values not how often each value appears You can cause duplicate rows to be suppressed by including the keyword DISTINCT or its synonym UNIQUE at the start of the select list as shown in Query 2 13 SELECT UNIQUE customer_num FROM orders SELECT DISTINCT customer_num FROM orders
303. ed in Chapter 10 Tuning Your Data Model Embedding Grant and Revoke Privileges One task related to data definition is done repeatedly the granting and revoking of privileges The reasons for this are discussed in Chapter 11 Granting and Limiting Access to Your Database Because privileges must be granted and revoked frequently and because this might be done by per sons who are not skilled in SQL it can be useful to package the GRANT and REVOKE statements in programs to give them a simpler more convenient user interface 5 34 Programming with SQL Figure 5 9 Embedding Data Definition Statements The GRANT and REVOKE statements are especially good candidates for dynamic SQL Each statement takes the following parameters e A list of one or more privileges e A table name The name of a user You probably need to supply at least some of these values based on program input from the user command line parameters or a file but none can be supplied in the form of a host variable The syntax of these statements does not allow host variables at any point The only alternative is to assemble the parts of a statement into a character string and prepare and execute the assembled statement Program input can be incorporated into the prepared statement as characters Figure 5 9 shows a function in INFORMIX 4GL that assembles a GRANT statement from the function parameters and then prepares and executes it FUNCTI
304. ed into total_price is returned by the RETURN statement at the conclusion of the stored procedure The total_price column is updated for each row that the triggering statement affects Tracing Triggered Actions 15 12 If a triggered action does not behave as you expect place it in a stored procedure and use the SPL TRACE statement to monitor its operation Before starting the trace you must direct the output to a file with the SET DEBUG FILE TO statement Figure 15 2 shows TRACE statements that have been added to the stored procedure items_pct The SET DEBUG FILE TO statement directs the trace output to the file usr mydir trig trace The TRACE ON statement begins tracing the statements and variables within the procedure Creating and Using Triggers Figure 15 2 Tracing Triggered Actions REATE PROCEDURE items_pct mac CHAR 3 EFINE tp MONEY EFINE mc_tot MONEY EFINE pct DECIMAL ET DEBUG FILE TO usr mydir trig trace RACE begin trace nNUUOAa 5 TRACE ON LET tp SELECT SUM total_price FROM items LET mc_tot SELECT SUM total_price FROM items WHERE manu_code mac LET pct mc_tot tp F pct gt 10 THEN RAISE EXCEPTION 745 END IF TRACE OFF END PROCEDURE CREATE TRIGGER items_ins INSERT ON items REFERENCING NEW AS post_ins FOR EACH ROW EXECUTE PROCEDURE items_pct post_ins manu_code w m Using a stored procedure to trace a trigg
305. ed matrix for an telephone directory Other decisions reflected in the matrix is that no relationship exists between a fax number and a modem number between a voice number and a fax or between a voice number and a modem number You might disagree with some of these decisions for example why a relationship between voice numbers and modem numbers is not supported For the sake of our example these are our business rules Diagramming Your Relationships For now save the matrix that you created in this section You will learn how to create an entity relationship diagram in Diagramming Your Data Objects on page 8 16 Identifying Attributes Entities contain attributes which are characteristics or modifiers qualities amounts or features An attribute is a fact or nondecomposable piece of information about an entity Later when you represent an entity as a table its attributes are added to the model as new columns 8 14 Building Your Data Model Identifying and Defining Your Principal Data Objects How to Identify an Attribute Before you can identify your attributes you must identify your entities After you determine your entities ask yourself what characteristics do you need to know about each entity For example in an address entity you probably need information about street city and zipcode Each of these characteristics of the address entity become attributes Selecting Attributes for Your Entities I
306. ed order number for each row in the table To access a row of data in the orders table you can use the following SELECT statement SELECT FROM orders WHERE order_num 1001 Using the order number in the WHERE clause of this statement enables you to access a row easily because the order number uniquely identifies that row If the table allowed duplicate order numbers it would be almost impossible to access one single row because all other columns of this table allow duplicate values Refer to Chapter 8 Building Your Data Model for more information on primary keys and entity integrity Semantic Integrity 4 18 Modifying Data Semantic integrity ensures that data entered into a row reflects an allowable value for that row This means that the value must be within the domain or allowable set of values for that column For example the quantity column of the items table permits only numbers If a value outside the domain can be entered into a column the semantic integrity of the data is violated Data Integrity Semantic integrity is enforced using the following constraints e Data type The data type defines the types of values that you can store in a column For example the data type SMALLINT allows you to enter values from 32 767 to 32 767 into a column e Default value The default value is the value inserted into the column when an explicit value is not specified For example the user_id column of the cus
307. ee Data type conversion AVG function as aggregate function 2 53T syntax in expression 1 462S use in expression 1 464S B Bachman C R 8 17T Backslash as escape character with LIKE 1 410S as escape character with MATCHES 1 411S Backup See Archive BEFORE keyword 1 116S BEGIN WORK statement locking in a transaction 1 35S specifies start of a transaction 4 24T syntax 1 358 BETWEEN keyword syntax in Condition segment 1 405S use in Condition segment 1 408S in SELECT 1 327S BETWEEN keyword used to test for equality in WHERE clause 2 29T BETWEEN operator 2 32T Binary Large Object BLOB choosing location for 10 18T disk storage for 10 4T 10 6T effect of isolation on retrieval 1 3685 estimating disk space for 10 17T in a LOAD statement 1 257S in an UNLOAD statement 1 379S See also BYTE data type See also TEXT data type blobspace 10 4T 10 18T BLOB See Binary Large Object Boolean expression and logical operator 2 36T in Condition segment 1 404S Bourne shell how to set environment variables 4 5R profile file 4 4R BUFFERED keyword syntax in SET LOG 1 372S BUFFERED LOG keywords syntax in CREATE DATABASE 1 57S use in CREATE DATABASE 1 598 Buffered logging 1 575 9 22T Building your data model 8 3T to 8 33T BYTE data type choosing location for 10 18T considerations for UNLOAD statement 1 379S description of 3 5R 9 19T disk storage for 10 4T estimating disk space for 10 17T inserting data 3 5R requiremen
308. either the name of a statement or the name of a cursor that was declared FOR a statement name and releases the space allocated to the prepared statement If more than one cursor is defined on the statement freeing the statement does not free the cursor Programming with SQL 5 33 Embedding Data Definition Statements Quick Execution Embedding For simple statements that do not require a cursor or host variables you can combine the actions of the PREPARE EXECUTE and FREE statements into a single operation The EXECUTE IMMEDIATE statement shown in the follow ing example takes a character string and in one operation prepares it executes it and frees the storage exec sql execute immediate drop index my_temp_index This makes it easy to write simple SQL operations However because no USING clause is allowed the EXECUTE IMMEDIATE statement cannot be used for SELECT statements Data Definition Statements Data definition statements the SQL statements that create databases and modify the definitions of tables are not usually put into programs The rea son is that they are rarely performed a database is created once but is queried and updated many times The creation of a database and its tables is generally done interactively using DB Access or INFORMIX SQL These tools can also be driven from a file of statements so that the creation of a database can be done with one operating system command This is discuss
309. eleting Through a View A modifiable view can be used with a DELETE statement as if it were a table The database server deletes the proper row of the underlying table Updating a View You can use a modifiable view with an UPDATE statement as if it were a table However a modifiable view can still contain derived columns that is col umns that are produced by expressions in the select list of the CREATE VIEW statement You cannot update derived columns sometimes called virtual columns When a column is derived from a simple arithmetic combination of a column with a constant value for example order_date 30 the database server can in principle figure out how to invert the expression in this case by sub tracting 30 from the update value and perform the update However much more complicated expressions are possible most of which cannot easily be inverted Therefore the database server does not support updating any derived column 11 24 Granting and Limiting Access to Your Database Figure 11 8 Using Views Figure 11 8 shows a modifiable view that contains a derived column and an UPDATE statement that can be accepted against it CREATE VIEW call_response user_id received resolved duration AS SELECT user_id call_dtime res_dtime res_dtime call_dtime FROM cust_calls WHERE user_id USER UPDATE call_response SET resolved TODAY WHERE resolved IS NULL A modifiable view and an UPDATE statement T
310. ely entered or it is not entered at all Archives and Logs By using transactions you can ensure that the database is always in a consistent state and that your modifications are properly recorded on disk But the disk itself is not perfectly safe It is vulnerable to mechanical failures and to flood fire and earthquake The only safeguard is to keep multiple copies of the data These redundant copies are called archive copies The transaction log also called the logical log complements the archive copy of a database Its contents are a history of all modifications that occurred since the last time the database was archived If it should ever be necessary to restore the database from the archive copy the transaction log can be used to roll the database forward to its most recent state Modifying Data 4 25 Archives and Logs Archiving with INFORMIX SE If a database is stored in operating system files INFORMIX SE archive copies are made using the normal methods for making backup copies in your operating system Only two special considerations exist for databases The first is a practical consideration A database can grow to great size It may become the largest file or set of files in the system It can also be awkward or very time consuming to make a copy of it You may need a special procedure for copying the database separate from the usual backup procedures and the job may not be done too frequently The second conside
311. ements end with a semicolon The same is true of INFORMIX ESQL C where the corresponding DELETE statement is written as shown in the fol lowing example EXEC SQL delete FROM items WHERE order_num onum In INFORMIX ESQL C an SQL statement can be introduced with either a leading dollar sign or the words EXEC SQL These differences of syntax are trivial the essential points in all languages an SQL API INFORMIX 4GL or SPL are described in the following list e You can embed SQL statements in a source program as if they were executable statements of the host language e You can use program variables in SQL expressions the way literal values are used If you have programming experience you can immediately see the possibilities In the example the order number to be deleted is passed in the variable onum That value comes from any source that a program can use it can be read from a file the program can prompta user to enter it or it can be read from the database The DELETE statement itself can be part of a subrou tine in which case onum can be a parameter of the subroutine the subroutine can be called once or repetitively Programming with SQL 5 7 Calling the Database Server In short when you embed SQL statements in a program you can apply all the power of the host language to them You can hide the SQL under a multitude of interfaces and you can embellish its functions in a multitude of ways Calling the Dat
312. en ordered yet by performing a subquery on the items table SELECT stock FROM stock WHERE NOT EXISTS SELECT FROM items WHERE stock stock_num items stock_num AND stock manu_code items manu_code Query 3 34 It returns the rows shown in Query Result 3 34 stock_num manu_code description unit_price unit unit_descr 01 PRC bicycle tires 88 00 box 4 box 02 SHM bicycle brakes 220 00 case 4 sets case 02 PRC bicycle brakes 480 00 case 4 sets case 05 PRC bicycle wheels 53 00 pair pair 06 PRC bicycle stem 23 00 each eac 07 PRC bicycle saddle 70 00 pair pair 08 SHM crankset 45 00 each eac 09 SHM pedal binding 200 00 case 4 pairs case 10 ANZ helmet 244 00 case 4 case 10 HRO helmet 260 00 case 4 case 12 SHM 12 spd assmbld 549 00 each eac 13 SHM 18 spd assmbld 685 90 each eac 201 KAR golf shoes 90 00 each eac 202 NKL metal woods 174 00 case 2 sets case 203 NKL irons wedge 670 00 case 2 sets case 205 NKL 3 golf balls 312 00 case 24 case 205 HRO 3 golf balls 312 00 case 24 case 301 NKL running shoes 97 00 each eac 301 HRO running shoes 42 50 each eac 301 PRC running shoes 75 00 each eac 301 ANZ running shoes 95 00 each eac 302 HRO ice pack 4 50 each eac 303 KAR socks 36 00 box 24 pairs box 305 HRO first aid kit 48 00 case 4 case 306 PRC tandem adapter 160 00 each eac 308 PRC twin jogger 280 00 each eac 309 SHM ear drops 40 00 case 20 case 310 SHM kick board 80 00 case 10 case 310 ANZ ki
313. enecks are developing It also comes with utility pro grams to analyze its use of disk storage In addition OnLine provides the sysmaster tables that contain information about an entire OnLine database server which might manage many databases For more information about the sysmaster tables see the INFORMIX OnLine Dynamic Server Administra tor s Guide 1 10 Introducing Database Features and SQL Important Database Terms Chapter 10 Tuning Your Data Model contains an overview of the INFORMIX OnLine Dynamic Server disk storage methods as part of the nec essary background information to the main topic All the details of using and managing OnLine are contained in the INFORMIX OnLine Dynamic Server Administrator s Guide Important Database Terms You should know two sets of terms before beginning the next chapter One set of terms describes the database and the data model the other set describes the computer programs that manage the database The Relational Model Tables Figure 1 4 Informix databases are relational databases In technical terms that means that the data model by which an Informix database is organized is based on the relational calculus devised by E F Codd In practical terms it means that all data is presented in the form of tables comprising rows and columns A database is a collection of information grouped into one or more tables A table is an array of data items organized into rows and columns
314. ent 1 2785 parameterizing for SQL identifiers 1 279S preparing GRANT 11 13T question mark as placeholder 1 273S releasing resources with FREE 1 208S restrictions with SELECT 1 276S statement identifier use 1 274S syntax 1 273S valid statement text 1 275S with concatenation operator 1 4328 Prepared statement describing returned values with DESCRIBE 1 162S executing 1 184S prepared object limit 1 274S valid statement text 1 275S See also PREPARE statement PREVIOUS keyword syntax in FETCH 1 194S use in FETCH 1 196S Primary ke definition of 8 22T Index 33 34 Index restrictions with 8 22T Primary key constraint 1 225 composite 8 23T data type conversion 1 288 defining column as 1 93S definition of 4 19T dropping 1 32S enforcing 1 86S modifying a column with 1 285 referencing 1 22S requirements for 1 205 1 935 rules of use 1 315 1 945 PRIMARY KEY keywords in ALTER TABLE 1 295 in ALTER TABLE statement 1 205 in CREATE TABLE 1 915 1 925 Primary site 12 20T Printing specifying print program with DBPRINT 4 24R PRIOR keyword syntax in FETCH 1 1945 use in FETCH 1 196S Privilege Alter 1 236S 11 8T and views 11 27T to 11 30T ANSI compliant databases 1 12R automating grants of 11 13T column level 11 10T Connect 1 2325 11 6T DBA 1 2335 11 7T default for stored procedures 14 14T default for table using CREATE TABLE 1 85S Delete 1 236S 11 8T 11 28T displaying 4 16T displaying with the INFO statement 1 2425 enc
315. ent of the SQLERRD array to the character offset into the file The particular fields of the SQLCA for each product are shown in the following table ESQL C ESQL FORTRAN ESQL COBOL sqlca sqlcode sqlcod SQLCODE OF SQLCA SQLCODE sqlca sqlerrd 4 sqlca sqlerr 5 SQLERRD 5 OF SQLCA Figure 14 3 shows how to trap for a syntax error when you are creating a procedure It also shows how to display a message and character position where the error occurred include lt stdio h gt Sinclude sqlca Sinclude sqlda Sinclude datetime Program to create a procedure from procfile in pwd main long char_num database play Screate procedure from procfile if sqlca sqlcode 0 printf nSqlca sqlcode ld n sqlca sqlcode char_num sqlca sqlerrd 4 printf nError in creating read_address Check character position ld n char_num Checking for failure when creating a procedure using ESQL C In Figure 14 3 if the CREATE PROCEDURE FROM statement fails the program displays a message in addition to the character position at which the syntax error occurred Creating and Using Stored Procedures 14 7 Creating and Using Stored Procedures Looking at Compile Time Warnings If the database server detects a potential problem but the procedure is syntactically correct the database server generates a warning and places it in a listing file You can examine this file to check for potential pro
316. ent variable 4 56R 12 14T termcap file and TERMCAP environment variable 4 56R selecting with INFORMIXTERM 4 39R Terminal handling and TERM environment variable 4 55R and TERMCAP environment variable 4 56R and TERMINFO environment variable 4 56R terminfo directory and TERMINFO environment variable 4 56R selecting with INFORMIXTERM 4 39R TERMINFO environment variable 4 56R TEXT data type choosing location for 10 18T description of 3 21R 9 17T disk storage for 10 4T estimating disk space for 10 17T inserting values 3 21R requirements for LOAD statement 1 257S restrictions with aggregate functions 3 21R with GROUP BY 3 21R 3 7T with IN clause 3 21R with LIKE or MATCHES 3 21R 2 37T with ORDER BY 3 21R with relational expression 2 29T selecting a column 3 22R syntax 1 425S use in Boolean expression 3 21R used for performance 10 27T with control characters 3 21R with LENGTH function 2 64T with stored procedures 2 95 2 135 Text editor specifying with DBEDIT 4 18R TEXT value displaying 2 11T Third normal form 8 32T Time function restrictions with GROUP BY 1 334S use in SELECT 1 314S Time representing with NLS 1 15R TO CLUSTER keywords in ALTER INDEX 1 12S TO keyword in expression 1 462S in GRANT 1 231S TODAY function syntax in Condition segment 1 405S in expression 1 436S in INSERT 1 250S use in ALTER TABLE 1 188 in constant expression 1 4395 2 63T 4 8T in CREATE TABLE 1 888 in INSERT 1 252S TP XA
317. ents The following keywords introduce a subquery in the WHERE clause of a SELECT statement e AIL e ANY e IN EXISTS You can use any of the relational operators with ALL and ANY to compare something to every one of ALL or to any one of ANY the values that the subquery produces You can use the keyword SOME in place of ANY The operator IN is equivalent to ANY To create the opposite search condition use the keyword NOT or a different relational operator The EXISTS operator tests a subquery to see if it found any values that is it asks if the result of the subquery is not null See Chapter 1 in the Informix Guide to SQL Syntax for the complete syntax used in creating a condition with a subquery See also Chapter 13 Optimizing Your Queries of this manual for information on performance implications for correlated and uncorrelated subqueries Using ALL Use the keyword ALL preceding a subquery to determine whether a comparison is true for every value returned If the subquery returns no val ues the search condition is true If it returns no values the condition is true of all of the zero values Composing Advanced SELECT Statements 3 33 Subqueries in SELECT Statements Query 3 27 lists the following information for all orders that contain an item for which the total price is less than the total price on every item in order number 1023 SELECT order_num stock_num manu_code total_price FROM ite
318. ents for LOAD statement 1 257S syntax 1 425S used for performance 10 26T using as default value 1 195 1 895 versus NVARCHAR data type 1 19R with LENGTH function 2 64T VARCHAR value displaying 2 11T Variable default values in SPL 2 1185 2 125 define in SPL 2 75 global in SPL 2 10S 14 17T in SPL 14 16T local in SPL 2 125 14 17T scope of SPL variable 2 8S unknown values in IF 2 25S with same name as a keyword 14 19T View creating a view 1 136S 11 20T creating synonym for 1 80S deleting rows in 11 24T description of 11 19T display description with dbschema 34R dropped when basis is dropped 11 22T dropping 1 183S effect of changing basis 11 23T effect on performance 13 33T inserting rows in 11 25T modifying 11 23T to 11 27T naming with NLS 1 15R null inserted in unexposed columns 11 25T privilege when accessing 11 28T privilege when creating 1 137S privileges 11 27T to 11 30T privileges with GRANT 1 239S produces duplicate rows 11 22T restrictions with UNION operator 1 3445 system catalog table 2 33R updatable 1 139S updating 1 384S updating duplicate rows 11 25T using CHECK OPTION 11 25T virtual column 1 1375S 11 24T with SELECT notation 1 136S View Name segment 1 510S Ww WAIT keyword in the SET LOCK MODE statement 1 370S WARNING keyword in the WHENEVER statement 1 398S Warnings with stored procedures at compile time 14 8T WEEKDAY function as time function 2 56T 2 60T syntax in expression 1 454S
319. equest and creates a temporary light gray arrows connection between the client and SE This temporary connection for example 3 1 enables the client and INFOR MIX SE database server to establish a direct connection 3 Then sqlexecd removes itself from the loop leaving the client attached to the SE database server Environment Variables The Informix administrator must make sure that each user sets the correct environment variables The following list shows the most important environment variables used by INFORMIX OnLine Dynamic Server and INFORMIX SE e PATH INFORMIXDIR INFORMIXSERVER TERM e DBPATH The INFORMIXDIR environment variable must be set to the full pathname of the directory where the Informix files reside The PATH environment variable must include the full pathname of the directory where the executables for INFORMIX SE and or INFORMIX OnLine Dynamic Server reside These two environment variables are required After the Informix administrator has specified them you usually do not change them The INFORMIXSERVER environment variable is the name of the default database server It is also a required variable You may choose to change INFORMIXSERVER when you change applications The TERM or TERMCAP and or INFORMIXTERM environment variable enables the clients to recognize and communicate with your terminal These variables are system and terminal dependent To set them you may need the assistance of your syste
320. er 1 of the Informix Guide to SQL Syn tax For information on building data models using primary and foreign keys refer to Chapter 8 Building Your Data Model Data Integrity Using the ON DELETE CASCADE Option You can maintain referential integrity when deleting rows from a primary key for a table by using the ON DELETE CASCADE option in the REFERENCES clause of the CREATE TABLE and ALTER TABLE statements This option allows you to delete a row from a parent table and its corresponding rows in matching child tables with a single delete command Locking During Cascading Deletes During deletes locks are held on all qualifying rows of the parent and child tables When you specify a delete the delete requested from the parent table occurs before any referential actions are performed What Happens to Multiple Children Tables If you have a parent table with two child constraints one child with cascading deletes specified and one child without cascading deletes and you attempt to delete a row from the parent table that applies to both child tables then the DELETE statement fails and no rows are deleted from either the parent or child tables Logging Must Be Turned On You must turn logging on in your current database for cascading deletes to work Logging and cascading deletes are discussed in Transaction Logging on page 4 24 Example Say you have two tables with referential integrity rules applied a parent table
321. er_num C customer_num then let Sum 0 for each row in the items table do read the row into I if IT order_num O order_num then let Sum Sum I total_price end if end for prepare an output row from C I and Sum end if end for end for A query plan in pseudocode 13 22 Optimizing Your Queries Time Costs of a Query This procedure reads the following rows e All rows of the customer table once e All rows of the orders table once for each row of the customer table e All rows of the items table once for each row of orders that appears in the output every row of orders should appear once This is not the only possible query plan another merely reverses the roles of customer and orders for each row of orders it reads all rows of customer looking for a matching customer_num It reads the same number of rows but in a different sequence A Join with Column Filters In the preceding example no difference exists in the amount of work that the two possible query plans need to do The presence of a column filter changes things A column filter is a WHERE expression that reduces the number of rows that a table contributes to a join The following example shows the preceding query with a filter added SELECT C customer_num O order_num SUM I total_price FROM customer C orders O items I WHERE C customer_num O customer_num AND O order_num I order_num AND O paid_date IS NULL GROUP BY C customer_num O order_num
322. er_num O order_num SUM I total_price FROM customer C orders O items I WHERE C customer_num O customer_num AND O order_num I order_num GROUP BY C customer_num O order_num Estimated Cost 102 Estimated of Rows Returned 1 Temporary Files Required For GROUP BY 1 pubs o SEQUENTIAL SCAN 2 pubs c INDEX PATH 1 Index Keys customer_num Key Only Lower Index Filter pubs c customer_num pubs o customer_num 3 pubs i INDEX PATH 1 Index Keys order_num Lower Index Filter pubs i order_num pubs o order_num Typical output produced by the optimizer with SET EXPLAIN ON The optimizer also reveals its estimate of the number of rows that the query produces In Figure 13 1 the optimizer incorrectly estimates 1 In this exam ple the estimate is incorrect because the optimizer has no way to estimate the number of groups the GROUP BY clause produces In the body of the explanation the optimizer lists the order in which tables are accessed and the method or access path by which it reads each table The following breakdown clarifies the plan 1 The orders table is read first Because no filter exists on the orders table all of its rows must be read that is reading the table in physical order is the least costly approach 2 For each row of orders a search is made for matching rows in the customer table The search uses the index on customer_num The notation Key Only means that because
323. ered action Creating and Using Triggers 15 13 Generating Error Messages Figure 15 3 shows sample trace output from the items_pct procedure as it appears in the file usr mydir trig trace The output reveals the values of procedure variables procedure arguments return values and error codes trace expression begin trace trace on expression select sum total_price from items evaluates to 18280 77 let tp 18280 77 expression select sum total_price from items where manu_code mac evaluates to 3008 00 let mc_tot 3008 00 expression mc_tot tp evaluates 0 16 let pct 0 1 expression evaluates expression evaluates raise exception Oy TI exception looking for handler SQL error 745 ISAM error 0 error string exception no appropriate handler Figure 15 3 Trace output from the items pct stored procedure See Chapter 14 Creating and Using Stored Procedures for more information on using the TRACE statement to diagnose logic errors in stored procedures Generating Error Messages When a trigger fails because of an SQL statement the database server returns the SQL error number that applies to the specific cause of the failure When the triggered action is a stored procedure you can generate error messages for other error conditions by using one of two reserved error num bers The first one is error number 745 which has a generalized and fixed error message The seco
324. erformed on the table the database server executes the SQL statements that make up the triggered action The trigger event can be an INSERT DELETE or UPDATE statement When you define an UPDATE trigger event you can name one or more columns in the table to activate the trigger If you do not name any columns then an update of any column in the table activates the trigger You can create only one INSERT and one DELETE trigger per table but you can create multiple UPDATE triggers as long as the triggering columns are mutually exclusive In the following excerpt of a CREATE TRIGGER statement the trigger event is defined as an update of the quantity column in the items table CREATE TRIGGER upqty UPDATE OF quantity ON items an UPDATE trigger event Notice that this portion of the statement identifies the table on which you create the trigger If the trigger event is an insert or delete only the type of statement and the table name are required as shown in the following example CREATE TRIGGER ins_qty INSERT ON items an INSERT trigger event Creating and Using Triggers 15 5 How to Create a Trigger Defining the Triggered Actions The triggered actions are the SQL statements that are performed when the trigger event occurs The triggered actions can consist of INSERT DELETE UPDATE and EXECUTE PROCEDURE statements In addition to specifying what actions are to be performed however you must also specify when
325. ero if no error occurs and to a negative error code if an error occurs The third element of SQLERRD is set to the number of rows actually inserted into the table It is set to zero if the new row is merely moved to the buffer to the count of rows that are in the buffer if the buffer load is inserted without error or to the count of rows inserted before an error occurs if one does occur Read the code Figure 6 4 once again to see how SQLCODE is used First if the OPEN statement yields an error the loop is not executed because the WHILE condition fails the FLUSH operation is not performed and the transaction rolls back Second if the PUT statement returns an error the loop ends because of the WHILE condition the FLUSH operation is not performed and the transaction rolls back This can occur only if the loop generates enough rows to fill the buffer at least once otherwise the PUT statement cannot generate an error The program might end the loop with rows still in the buffer possibly without inserting any rows At this point the SQL status is zero and the FLUSH operation occurs If the FLUSH operation produces an error code the transaction rolls back Only when all inserts are successfully performed is the transaction committed Rows of Constants The insert cursor mechanism supports one special case where high performance is easy to obtain This is the case in which all of the values listed in the INSERT statement are c
326. ers who have few or no table privileges to have DBA privileges when they execute the proce dure In the procedure users can carry out very specific tasks with their tem porary DBA privilege The DBA privileged feature allows you to accomplish the following tasks e You can restrict how much information individual users can read from a table e You can restrict all the changes made to the database and ensure that entire tables are not emptied or changed accidentally e You can monitor an entire class of changes made to a table such as deletions or insertions e You can restrict all object creation data definition to occur within a stored procedure so that you have complete control over how tables indexes and views are built Granting and Limiting Access to Your Database 11 15 Controlling Access to Data Using Stored Procedures Restricting Reads of Data The procedure in Figure 11 3 hides the SQL syntax from users but it requires that users have the Select privilege on the customer table If you want to restrict what users can select you can write your procedure to work in the following environment You are the DBA of the database The users have the Connect privilege to the database They do not have the Select privilege on the table e Your stored procedure or set of stored procedures is created using the DBA keyword e Your stored procedure or set of stored procedures reads from the table for users If
327. ers1 purchl 004 8006 004 8006 004 8006 005 2865 005 2865 005 2865 007 278693 007 278693 007 278693 007 278693 007 278693 007 278693 012 278701 012 278701 013 B77930 017 DM354331 018 S22942 018 S22942 019 255709 019 255709 019 255709 023 KF2961 Query Result 3 10 You can join a table to itself more than once The maximum number of shipl 05 30 05 30 05 30 06 09 06 09 06 09 06 05 06 05 06 05 06 05 06 05 06 05 06 29 06 29 07 10 07 13 07 13 07 13 07 16 07 16 07 16 07 30 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 orders2 purch2 B77897 W2286 w9925 B77897 W2286 w9925 B77836 4745 B77897 MA003 W2286 w9925 B77897 W2286 B77897 B77897 B77897 W2286 B77897 W2286 w9925 B77897 self joins depends on the resources available to you Composing Advanced SELECT Statements ship2 07 03 07 6 07 30 07 03 07 6 07 30 06 01 06 21 07 03 07 07 6 6 07 30 07 03 07 6 07 03 07 03 07 03 07 6 07 03 07 6 07 30 07 03 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 993 3 13 Creating Advanced Joins The self join in Query 3 11 creates a list of those items in the stock table that are supplied by three manufacturers By including the last two conditions
328. ery 2 19 Composing Simple SELECT Statements 2 25 Single Table SELECT Statements The collation order for the results of this query may vary depending on whether NLS is activated and the settings for the LANG and LC_COLLATE environment variables as well as how uppercase versus lowercase letters are handled by the particular system Query Result 2 19a and Query Result 2 19b show two sample sets of output num ro nom 13612 Azevedo 13606 Dupr 13607 Hammer 13602 H mmerle 13604 LaFor t 13610 LeMaitre 13613 Llanero 13603 Monta a 13611 Oatfield 13609 Tiramis 13600 da Sousa 13615 di Girolamo 13601 lesund 13608 taix 13605 tker 13614 verst Query Result 2 19a 2 26 Composing Simple SELECT Statements pr nom Edouardo Freire Mich le Fran oise Gerhard Greta Jean No l H lo se Gloria Dolores Jos Antonio Emily Paolo Alfredo Jo o Louren o Antunes Giuseppe Sverre mile Hans J rgen Per Anders Single Table SELECT Statements Query Result 2 19a follows the standard ASCII sorting order which ranks capital letters before lowercase letters and moves the names that start with a capitalized foreign character Alesund Etaix Otker and verst to the end of the list num ro nom pr nom 13601 Alesund Sverre 13612 Azevedo Edouardo Freire 13600 da Sousa Joao Louren o Antunes 13615 di Girolamo Giuseppe 13606 Dupr ich le Fran oise 13608 Etaix Emile 13607 Hammer Gerhard
329. es 14 17T placement of 2 85 syntax 2 75 DELETE keyword syntax in GRANT 1 235S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 302S Delete privilege 1 235S 11 8T 11 28T DELETE REFERENCING clause and FOR EACH ROW section 1 121S correlation name 1 119S syntax 1 119S DELETE statement all rows of table 4 4T and end of data 6 14T applied to view 11 24T as triggering statement 1 1125 cascading 1 160S coordinated deletes 6 6T count of rows 6 4T CURRENT OF clause 1 161S description of 4 4T embedded 5 6T 6 3T to 6 8T in trigger event 1 111S in triggered action 1 122S number of rows 5 12T preparing 5 30T privilege for 1 235S 11 6T 11 8T syntax 1 159S time to update indexes 10 20T transactions with 6 5T using subquery 4 6T WHERE clause restricted 4 6T with Condition segment 1 404S with cursor 1 152S 6 7T with select for update 1 340S within a transaction 1 159S Delete cascading See Cascading deletes Delimiter for DATETIME values 3 9R for INTERVAL values 3 15R for LOAD input file 1 258S specifying with UNLOAD 1 380S Delimiter form of FILE and INSERT statements 5 24R DELIMITER keyword in LOAD 1 258S in UNLOAD 1 380S Demonstration database copying Intro 10R Intro 135 8T installation script Intro 9R Intro 12S 7T map of A 6R overview Intro 9R Intro 12S 7T structure of tables A 2R tables in A 2R to A 6R See also stores6 database Denormalizing 10 26T Derived data introduced
330. es a null value Null values can be stored in the database but the data types supported by programming languages do not recognize a null state A program must have some way of recognizing a null item to avoid processing it as data Indicator variables meet this need in the SQL APIs An indicator variable is an additional variable that is associated with a host variable that might receive a null item When the database server puts data in the main variable it also Programming with SQL 5 15 Retrieving Single Rows puts a special value in the indicator variable to show whether the data is null In the following INFORMIX ESQL C example a single row is selected and a single value is retrieved into the host variable op_date exec sql select paid_date into op_date op_d_ind from orders where order_num S the_order if op_d_ind lt 0 data was null rstrdate 01 01 1900 op_date Because the value might be null an indicator variable named op_d_ind is associated with the host variable It must be declared as a short integer elsewhere in the program Following execution of the SELECT statement the program tests the indicator variable for a negative value A negative number usually 1 means that the value retrieved into the main variable is null If that is the case this program uses a C function to assign a default value to the host variable The function rstrdate is part of the INFORMIX ESQL C product The syntax y
331. es how to invoke the utility to access modify and retrieve information from Informix database servers When errors occur you can look them up by number and learn their cause and solution in the Informix Error Messages manual If you prefer you can look up the error messages in the on line message file described in the section ASCII and PostScript Error Message Files later in this Introduction How to Use This Manual How to Use This Manual This manual assumes that you are using INFORMIX OnLine Dynamic Server as your database server Features and behavior specific to INFORMIX SE are noted throughout the manual Other conventions used in this manual for typographical format and example code are described in the following sections Typographical Conventions Informix product manuals use a standard set of conventions to introduce new terms illustrate screen displays describe command syntax and so forth The following typographical conventions are used throughout this manual italics New terms emphasized words and variables are printed in italics boldface Database names table names column names filenames utilities and other similar terms are printed in boldface computer Information that the product displays and information that you enter are printed in a computer typeface KEYWORD All keywords appear in uppercase letters information that if ignored could cause harm to your This symbol indicates a warning
332. escribed in the following list 1 Drop the table if it exists 2 Create the table without specifying any unique constraints 3 Load all rows into the table 4 Alter the table to apply the unique constraints 5 Create the non unique indexes If you cannot guarantee that the loaded data satisfies all unique constraints you must create the unique indexes before you load the rows It saves time if the rows are presented in the correct sequence for at least one of the indexes if you have a choice make it the one with the largest key This minimizes the number of leaf pages that must be read and written 10 24 Tuning Your Data Model Managing Indexes Clustered Indexes The term clustered index is a misnomer The index is nothing special it is the table that is modified so that its rows are physically ordered to agree with the sequence of entries in the index Do not confuse the clustered index with an optical cluster which is a method for storing logically related blobs together on an optical volume For information on optical clusters see the INFORMIX OnLine Optical User Manual When you know that a table is ordered by a certain index you can take advantage of the knowledge to avoid sorting You can also be sure that when the table is searched on that column it is read effectively in sequential order instead of nonsequentially These points are covered in Chapter 13 Optimizing Your Queries In the stores6 datab
333. escription of 4 27T 7 3T Dirty Read isolation 1 367S 7 10T effect on performance 7 3T isolation level 7 9T kinds of locks 7 6T lock duration 7 8T lock scope 7 6T maximizing 10 32T 10 35T Repeatable Read isolation 1 3675 7 12T SERIAL values 9 7T table lock 7 7T Condition segment ALL ANY SOME subquery 1 415S boolean expressions 1 405S comparison condition 1 405S description of 1 404S join conditions 1 331S null values 1 405S relational operators in 1 407S subquery in SELECT 1 413S syntax 1 404S use of functions in 1 405S wildcards in searches 1 410S with BETWEEN keyword 1 408S with ESCAPE keyword 1 411S with EXISTS keyword 1 414S with IN keyword 1 408S with IS keyword 1 409S with MATCHES keyword 1 409S with NOT keyword 1 410S Configuring a database server 12 15T CONNECT keyword in GRANT 1 2325 in REVOKE 1 303S Connect privilege 1 2325 1 303S 11 6T CONNECT statement and INFORMIXSERVER environment variable 4 37R 1 46S connection context 1 45S connection identifiers 1 45S database environment 1 49S DEFAULT option 1 465 implicit connections 1 465 opening a database 12 16T syntax 1 445 use 1 44S USER clause 1 52S WITH CONCURRENT TRANSACTION option 1 475 CONNECT TO statement with concatenation operator 1 4325 Connecting to data 12 12T Index 7 8 Index Connection context 1 45S dormant 1 169S identifiers 1 45S setting the INFORMIXCONRETRY environment variable 4 34R
334. estions for increasing concurrency among multiple programs INFORMIX OnLine Dynamic Server Disk Storage OnLine manages disk storage directly To the greatest extent possible it bypasses the host operating system and works with the raw disk space The extent to which this is possible depends on the operating system Tuning Your Data Model 10 3 INFORMIX OnLine Dynamic Server Disk Storage device 0x7d blobspace rasters device x7r dbspace root dbspace temps Figure 10 1 The relationship between chunks and dbspaces Its methods of disk management are not complicated However several terms are used for different amounts of space in varying contexts the chunk the dbspace or blobspace the page the extent and the tblspace Chunks and Pages The basic unit of physical storage is the chunk A chunk is a unit of disk storage that is dedicated to OnLine Usually it is a physical device that is a disk drive However a chunk can be part of one disk or simply a file In any case a chunk is a unit of space that can be identified to the operating system as being in the exclusive control of OnLine The page is the basic unit of disk input output I O All space in every chunk is divided into pages All I O is done in units of whole pages The size of a page is the same in all chunks used for tables It is set when an OnLine system is installed Dbspaces and Blobspaces A space always comprises one or more complete chunks O
335. eturned by the SELECT statement e Calculated values the VALUES clause only permits constants because the select list can contain expressions Modifying Data 4 9 Statements That Modify Data For example suppose a follow up call is required for every order that has been paid for but not shipped The INSERT statement in the following exam ple finds those orders and inserts a row in cust_calls for each order INSERT INTO cust_calls customer_num call_descr SELECT customer_num order_num FROM orders WHERE paid_date IS NOT NULL AND ship_date IS NULL This SELECT statement returns two columns The data from these columns in each selected row is inserted into the named columns of the cust_calls table Then an order number from order_num a serial column is inserted into the call description which is a character column Remember that the database server allows you to insert integer values into a character column It automat ically converts the serial number to a character string of decimal digits Restrictions on the Insert Selection 4 10 Modifying Data The following list contains the restrictions on the SELECT statement for insert ing rows It cannot contain an INTO clause It cannot contain an INTO TEMP clause e It cannot contain an ORDER BY clause Itcannot refer to the table into which you are inserting rows The INTO INTO TEMP and ORDER BY clause restrictions are minor The INTO clause is not usef
336. eve remarkable time savings in this way Even if no time is saved the necessary study of the application and the query at least make it clear where the time is being spent 13 42 Optimizing Your Queries Creating and Using Stored Procedures Chapter Overview 3 Introduction to Stored Procedures and SPL 3 What You Can Do with Stored Procedures 3 Relationship Between SQL and a Stored Procedure 4 Creating and Using Stored Procedures 4 Creating a Procedure Using DB Access 5 Creating a Procedure Using anSQL API 5 Commenting and Documenting a Procedure 6 Diagnosing Compile Time Errors 6 Finding Syntax Errors in a Procedure Using DB Access 6 Finding Syntax Errors in a Procedure Using an SQL API 7 Looking at Compile Time Warnings 8 Generating the Text or Documentation 8 Looking at the Procedure Text 9 Looking at the Procedure Documentation 9 Executing a Procedure 9 Executing a Stored Procedure Dynamically 11 Debugging a Procedure 11 Re creating a Procedure 13 Privileges on Stored Procedures 13 Privileges Necessary at Creation 14 Privileges Necessary at Execution 14 Owner Privileged Procedures 15 DBA Privileged Procedures 15 Privileges and Nested Procedures 16 Revoking Privileges 16 Variables and Expressions 16 Variables 16 Format of Variables 16 Global and Local Variables 17 Defining Variables 17 Data Types for Variables 17 Using Subscripts with Variables 18 Scope of Variables 18 Variable Keyword Ambiguity 19 SPL Ex
337. evels of merge the sort must use a factor that depends on the number of sort keys that can be held in memory When all the keys can be held in memory m 1 and the disk work is proportional to 2n In other words the rows are read sorted in memory and written When building an index only index pages are written For tables from moderate to large sizes rows are sorted in batches that fit in memory and then the batches are merged When m 2 the rows are read sorted and written in batches Then the batches are read again and merged and written again resulting in disk work proportional to 4n For extremely large tables the batches must be broken into batches The disk work is then pro portional to 6n In short as table size increases there are sudden discontinuous changes in the amount of disk work in a sort from 2n to 4n to 6n The table size at which these steps occur depends on many factors only one of which key size is in your control The best way to reduce the cost of sorting is to find a way to sort fewer rows because the factor n dominates both expressions When that is not possible look for ways to sort on fewer and nar rower columns Not only does this reduce the factors c and w it also defers the step to the next merge level Sorting involves writing information temporarily to disk You can direct the disk writes to occur in a dbspace managed by INFORMIX OnLine Dynamic Server or an operating system file Writ ing to a db
338. events such as these using the locking and isolation level features of the database server How Locks Work The INFORMIX OnLine Dynamic Server database server supports a complex flexible set of locking features that is described in this section Some of these locking features work differently on an INFORMIX SE database server See Chapter 1 of the Informix Guide to SQL Reference for a summary of the differences between locking in SE and OnLine database servers Programming for a Multiuser Environment 7 5 How Locks Work Kinds of Locks INFORMIX OnLine Dynamic Server supports the following three kinds of locks which it uses in different situations shared A shared lock reserves its object for reading only It prevents the object from changing while the lock remains More than one program can place a shared lock on the same object exclusive An exclusive lock reserves its object for the use of a single program It is used when the program intends to change the object An exclusive lock cannot be placed where any other kind of lock exists Once one has been placed no other lock can be placed on the same object promotable A promotable lock establishes the intent to update It can only be placed where no other promotable or exclusive lock exists Promotable locks can exist with shared locks They are promoted to an exclusive lock Lock Scope You can apply locks to entire databases entire tables disk pages single ro
339. ex 41 42 Index SQL SELECT and LC_COLLATE 4 51R SQL UNLOAD and DBDELIMITER 4 18R SQL UPDATE STATISTICS and DBUPSPACE 4 30R Statement identifier associating with cursor 1 148S definition of 1 2745 releasing 1 274S syntax in DECLARE 1 145S in DESCRIBE 1 162S in EXECUTE 1 1845S in FREE 1 2075 in PREPARE 1 2735 use in DECLARE 1 154S in FREE 1 2085 in PREPARE 1 2745 Statement types 1 5S Statement variable name definition 1 190S Static SQL 5 5T STATUS FOR keywords in INFO statement 1 2445 STATUS variable 4GL 5 11T Status displaying with INFO statement 1 2445 stock table in stores6 database columns in A 4R STOP keyword in the WHENEVER statement 1 398S 1 402S Storage device 12 6T Stored procedure altering 14 13T as triggered action 1 128S 15 10T branching 14 22T BYTE and TEXT data types 2 95 2 138 checking references 1 1295 comments in 14 6T creating from an embedded language 14 5T creating from DB Access 14 5T cursors with 2 205 DBA privileged use with triggers 1 129S 14 13T debugging 2 425 14 11T default privileges 14 14T DEFINE statement 14 17T definition of 14 3T displaying contents 14 9T displaying documentation 14 9T executing 14 9T general programming 1 17T granting privileges on 1 237S 11 12T 14 15T handling multiple rows 2 398 header 2 8S 14 25T in SELECT statements 1 315S 2 67T in WHEN condition 1 122S introduction to 14 3T looping 14 23T name confusion with SQL functio
340. examples specifies the manatee table created by the owner bubba which resides in an ANSI compliant database named syzygy For more information on defining external tables see Chapter 1 in the Informix Guide to SQL Syntax Composing Simple SELECT Statements 2 37 Single Table SELECT Statements Each statement in Query 2 29 retrieves all the rows that have the single word helmet in the description column SEL ti O20 FROM syzygy bubba manatee ERE description helmet RDER BY mfg_code a I SEL GI O20 FROM syzygy bubba manatee HERE description LIKE helmet RDER BY mfg_code x I SEL LE Oza FROM syzygy bubba manatee HERE description MATCHES helmet RDER BY mfg_code Query 2 29 stock_no mfg_code description unit_price unit unit_type 991 ANT helmet 222 00 case 4 case 991 BKE helmet 269 00 case 4 case 991 JSK helmet 311 00 each 4 case 991 PRM helmet 234 00 case 4 case 991 SHR helmet 245 00 case 4 case Query Result 2 29 Using a Single Character Wildcard The statements in Query 2 30 illustrate the use of a single character wildcard in a WHERE clause Further they demonstrate a query on an external table The stock table is in the external database sloth which beside being outside the current stores6 database is on a separate database server called meerkat 2 38 Composing Simple SELECT Statements Single Table SELEC
341. ey all have been dropped 11 22 Granting and Limiting Access to Your Database Using Views When a table is renamed any views in the same database that depend on it are modified to use the new name When a column is renamed views in the same database that depend on that table are updated to select the proper col umn However the names of columns in the views themselves are not changed For an example of this recall the following view on the customer table CREATE VIEW name_only AS SELECT customer_num fname lname FROM customer Now suppose that the customer table is changed in the following way RENAME COLUMN customer lname TO surname To select last names of customers directly you must now select the new column name However the name of the column as seen through the view is unchanged The following two queries are equivalent SELECT fname surname FROM customer SELECT fname lname FROM name_only When you alter a table by dropping a column views are not modified If they are used error 217 Column not found in any table in the query occurs The reason views are not dropped is that you can change the order of columns in a table by dropping a column and then adding a new column of the same name If you do this views based on that table continue to work They retain their original sequence of columns INFORMIX OnLine Dynamic Server permits you to base a view on tables and views in external dat
342. ey or update it with a different primary key you destroy the meaning of any rows that contain that value as a foreign key Referential integrity is the logical dependency of a foreign key on a primary key The integrity of a row that contains a foreign key depends on the integrity of the row that it references the row that contains the matching primary key Modifying Data 4 19 Data Integrity By default INFORMIX OnLine Dynamic Server does not allow you to violate referential integrity and gives you an error message if you attempt to delete rows from the parent table before you delete rows from the child table You can however use the ON DELETE CASCADE option to cause deletes from a parent table to trip deletes on child tables See Using the ON DELETE CASCADE Option on page 4 21 customer Table detail customer_num fname Iname 103 Philip Currie 106 George Watson orders Table detail order_num order_date customer_num 1002 05 21 1993 101 1003 05 22 1993 104 1004 05 22 1993 106 cust_calls Table detail customer_num call_dtime user_id 106 1993 06 12 8 20 maryj 110 1993 07 07 10 24 riche 119 1993 07 01 15 00 riche Figure 4 1 Referential integrity in the stores6 database 4 20 Modifying Data You can define primary and foreign keys and the relationship between them using the CREATE TABLE and ALTER TABLE statements For more informa tion on these statements refer to Chapt
343. f data from a table Whenever data is exchanged over a network delays are inevitable in the following situations e Ifthe network is busy the sender must wait its turn to transmit Such delays are typically less than a millisecond But in a heavily loaded net work they can increase exponentially to tenths of seconds and more The responder may be handling requests from more than one sender so when the request arrives it may be queued for a time that can range from milliseconds to seconds When the responder acts on the request it incurs the time costs of disk access and in memory operations as described in the preceding topics e Transmission of the response is again subject to network delays The important point about network access is its extreme variability In the best case when neither the network nor the responder is busy transmission and queueing delays are insignificant and the responder sends a row almost as quickly as a local database server could do it Furthermore when the sender asks for a second row the page is likely still to be in the responder page buffers Unfortunately as network load increases all these factors tend to worsen at the same rate Transmission delays rise in both directions The queue at the responder gets longer And the odds of a page remaining in the responder buffer become worse Thus network access costs can change quite suddenly from very low to extremely high The optimizer that
344. f join 1 333S 3 11T sort merge 13 27T subservient table 3 21T two table join 1 332S Join column See Foreign key Join condition See Condition segment Journal updates 10 33T Index 25 26 Index K Key lock 7 8T Keywords using in triggered action 1 123S Key candidate See Candidate key Key composite 8 23T Key foreign See Foreign key Key primary 8 22T Key primary See Primary key constraint Korn shell how to set environment variables 4 5R profile file 4 4R L Label 2 49T 3 48T LANG environment variable 1 16R 4 49R Language supplement for added NLS functionality 1 22R LAST keyword syntax in FETCH 1 1945 use in FETCH 1 196S Latency 13 17T LC_COLLATE environment variable 1 16R 4 50R LC_CTYPE environment variable 1 16R 4 51R LC_MONETARY environment variable 1 17R 4 52R LC_NUMERIC environment variable 1 17R 4 53R LC_TIME environment variable 1 17R 4 53R LENGTH field setting with SET DESCRIPTOR 1 357S with DATETIME and INTERVAL types 1 358S with DECIMAL and MONEY types 1 358S LENGTH function in expression 1 314S on TEXT 2 64T on VARCHAR 2 64T syntax in expression 1 443S 1 453S use in expression 1 4535 2 63T LET statement assigning values 14 21T executing a procedure 14 9T syntax 2 28S LIKE keyword syntax in Condition segment 1 405S use in SELECT 1 328S wildcard characters 1 328S LIKE keyword used to test for equality in WHERE clause 2 29T LIKE relational operator 2 37T LIKE te
345. f this kind shown in Query 2 3 returns some of the rows and some of the columns in a table SELECT UNIQUE city state zipcode FROM customer WHERE state NJ Query 2 3 Composing Simple SELECT Statements 2 7 Introducing the SELECT Statement Joining Query Result 2 3 contains a subset of the rows and a subset of the columns in the customer table city state zipcode Cherry Hill NJ 08002 Princeton NJ 08540 Query Result 2 3 A join occurs when two or more tables are connected by one or more columns in common creating a new table of results Query 2 4 uses a subset of the items and stock tables to illustrate the concept of a join as shown in Figure 2 1 2 8 Composing Simple SELECT Statements Introducing the SELECT Statement SELECT unique item_num order_num FROM items stock WHERE items stock_num stock stock_num stock stock_num description items Table example item_num order_num stock_num 1 1001 stock Table example stock_num manu_code description HRO baseball gloves baseball gloves HRO baseball HSK football 5 NRG tennis racquet 2 1002 3 3 1003 5 1 1005 5 LD OOO item_num order_num stock_num description 1 1001 K g baseball gloves 1 1002 4 football 3 1003 5 tennis racquet 1 1005 5 tennis racquet Figure 2 1 Example of a join between two tables Query 2 4
346. ferenced objects In addition the database server verifies that you have the necessary privileges on the referenced objects If you execute a procedure that only references objects that you own no privilege conflicts occurs If you do not own the referenced objects and you execute a procedure that contains say SELECT statements for example you need the Select privilege on the appropriate tables to run the procedure without generating errors If the owner has the necessary privileges with the WITH GRANT option those privileges are automatically conferred to you when the owner issues a GRANT EXECUTE statement Unqualified objects created in the course of the procedure are owned by the owner of the procedure not the user running the procedure For example the following example shows lines in an owner privileged stored procedure that create two tables If this procedure is owned by tony and a user marty runs the procedure the first table gargantuan is owned by tony The second table tiny is owned by libby The table gargantuan is an unqualified name there fore tony owns the table gargantuan The table tiny is qualified by the owner libby so libby owns the table tiny CREATE PROCEDURE tryit CREAT CREAT ABLE gargantuan coll INT col2 INT col3 INT ABLE libby tiny coll INT col2 INT col3 INT c 22 END PROCEDURE DBA Privileged Procedures When you execute a DBA privileged procedu
347. ffer is full This reduces the amount of communication between the program and the data base server and it lets the database server insert the rows with less difficulty As a result the insertions go faster The minimum size of the insert buffer is set for any implementation of embedded SQL you have no control over it it is typically 1 or 2 kilobytes The buffer is always made large enough to hold at least two rows of inserted values It is large enough to hold more than two rows when the rows are shorter than the minimum buffer size Modifying Data Through SQL Programs 6 9 Using INSERT Inserting with a Cursor Figure 6 4 The code in Figure 6 3 prepares an insert cursor for use The continuation shown in Figure 6 4 shows how the cursor can be used For simplicity this example assumes that a function named next_cust returns either information about a new customer or null data to signal the end of input WHENEVER ERROR CONTINUE do not terminate on error BEGIN WORK OPEN new_custs WHILE status 0 CALL next_cust RETURNING the_company the_fname the_lname IF the_company IS NULL THEN EXIT WHILE END IF PUT new_custs END WHILE t F IF status 0 THEN no problem in a PUT LUSH new_custs write any last rows END IF IF status 0 THEN no problem writing COMMIT WORK make it permanent ELSE ROLLBACK WORK retract any changes END IF Continuing Figure 6 3 the 4GL code that uses the insert
348. for distributed database processing Advantages and Disadvantages of Distributed Databases You may find distributed databases useful because operations that use databases are often naturally distributed into separate pieces either organi zationally geographically or both A distributed database system includes the following advantages Local data can be kept locally where it is most easily maintained and most frequently used e Data from remote sites is available to all users e Duplicate copies can be maintained for safety of the data A distributed database system has the following disadvantages e Management of the distributed system is more involved than management of a single host system Network access is slower than local access Distributed Databases Using Multiple Vendor Servers You need INFORMIX TP XA if you use database management systems from multiple vendors to store your data and you want to use one application to access the data INFORMIX TP XA is a library of functions that allows the INFORMIX OnLine Dynamic Server database server to act as a resource man ager in a distributed transaction processing DTP environment that follows an interface standard which was defined by the X Open Company The terminology used by the XA standard is different from the terminology used by Informix products and documentation A transaction manager acts as an intermediary and relays requests from a user interface to a resource
349. for each row in the orders table do read the row into O if O paid_date is null and O customer_num C customer_num then let Sum 0 for each row in the items table do read the row into I if I order_num O order_num then let Sum Sum I total_price end if end for prepare an output row from C I and Sum end if end for The alternative query plan in pseudocode Because the filter is not applied in the first step shown in Figure 13 4 this plan reads the following rows e All rows of the customer table once e All rows of the orders table once for every row of customer e All rows of the items table pdnull times The query plans in Figure 13 3 and Figure 13 4 produce the same output although in different sequences They differ in that one reads a table pdnull times and the other reads a table SELECT COUNT x FROM customer times The choice the optimizer makes between them could make a difference of thousands of disk accesses in a real application Optimizing Your Queries 13 25 Time Costs of a Query Using Indexes Figure 13 5 The preceding examples do not use indexes or constraints which is unrealistic Almost all tables have one or more indexes or constraints and their presence makes a difference in the query plan Figure 13 5 shows the outline of a query plan for the previous query as it might be constructed using indexes Also see The Structure of an Index on page 13 20 for each row in the c
350. formix products 1 22R functionality listed 1 15R installation notes for language supplement 1 22R Index 29 N N N N N N N N N N 30 Index LANG environment variable 4 49R LC_COLLATE environment variable 4 50R LC_CTYPE environment variable 4 51R LC_MONETARY environment variable 4 52R LC_NUMERIC environment variable 4 53R LC_TIME environment variable 4 53R NCHAR data type 3 17R NVARCHAR data type 3 18R populating with dbimport 5 18R setting environment variables 1 16R 4 44R specifying a language environment 25 viewing characteristics of 1 18R LS Database description of 1 16T LS database versus non NLS database 1 19R ondecomposable attributes 8 15T onsequential access See Disk access nonsequential ormal form 8 29T ormalization benefits 8 29T first normal form 8 29T of data model 8 29T rules 8 29T rules summary 8 32T second normal form 8 31T third normal form 8 32T OT CLUSTER keywords syntax in ALTER INDEX 1 12S use in ALTER TABLE 1 13S OT FOUND keywords in the WHENEVER statement 1 398S 1 400S OT IN keywords use in Condition subquery 1 4145 OT keyword syntax in Condition segment 1 404S 1 405S with BETWEEN keyword 1 3275 with IN keyword 1 329S use in Condition segment 1 410S with LIKE MATCHES keywords 1 328S NOT logical operator 2 36T NOT NULL keywords syntax in ALTER TABLE 1 178 in CREATE TABLE 1 888 use in ALTER TABLE 1 278 in CREATE TABLE 1 908 9 24T wi
351. ften a space contains exactly one chunk so that the space and the chunk are identical However when a space comprises more than one chunk OnLine makes the multiple chunks appear to be a single sequence of pages A space is either a dbspace or a blobspace depending on its use If a space contains databases and tables it is a dbspace If it is dedicated to holding blobs the TEXT and BYTE data types it is a blobspace Chunks are assigned to a space when it is created Chunks also can be added to a space later 10 4 Tuning Your Data Model INFORMIX OnLine Dynamic Server Disk Storage One dbspace the root dbspace is created first and always exists It is the most important space because it holds the control information that describes all other spaces and chunks Parts of a single database can appear in two or more dbspaces However a single table is always completely contained in one dbspace Disk Mirroring Individual spaces can be mirrored The chunks of a mirrored space are paired with other chunks of equal size Whenever a page is written to one of the chunks it is also written to the mirror chunk When one chunk suffers a hard ware failure the database server uses its mirror to continue processing with out interruption When the broken chunk is restored to service or when a substitute chunk is assigned OnLine automatically brings it back to equality with the working chunk and continues operations When any dbspaces are
352. g Concurrency The integrity risk is simply that the redundant copies of the data might not be accurate If a lead time is changed in manufact the stock column is out dated until it too is updated As with derived data you should take pains to define the conditions under which the redundant data might be wrong Maximizing Concurrency 10 32 Some databases are used by only one program at a time others are used concurrently by multiple programs The following factors make concurrent programs inherently slower than doing the same amount of work serially e Multiple programs interfere with the use of buffers and disk drives The pages read for one program might be driven from the buffers used by a query from the next program and might have to be read again Disk I O for one query displaces the disk access arm slowing the sequential access of another program e Programs that modify data lock pages delaying all other programs that use the same data Easing Contention Contention is inevitable between programs using the same resources You can deal with it in the following ways 1 Make programs use fewer resources either by making them do less work or by making them work more efficiently 2 Arrange the resources better for instance by allocating tables to dbspaces to minimize contention 3 Supply more resources more memory more and faster disk drives and more and faster computers The first point is the subject of Ch
353. g Single Rows The declaration of the receiving variable avg_price in the previous example of ESQL C code is not shown It could be any one of the following definitions int avg_price double avg_price char avg_price 16 dec_t avg_price typedef of decimal number structure The data type of each host variable used in a statement is noted and passed to the database server along with the statement The database server does its best to convert column data into the form used by the receiving variables Almost any conversion is allowed although some conversions cause a loss of precision The results of the preceding example differ depending on the data type of the receiving host variable as described in the following list FLOAT The database server converts the decimal result to FLOAT possibly truncating some fractional digits If the magnitude of a decimal exceeds the maximum magnitude of the FLOAT format an error is returned INTEGER The database server converts the result to integer truncating fractional digits if necessary If the integer part of the converted number does not fit the receiving variable an error occurs CHARACTER The database server converts the decimal value to a character string If the string is too long for the receiving variable it is truncated The second field of SQLAWARN is set to W and the value in the SQLSTATE variable is 01000 Dealing with Null Data What if the program retriev
354. g Your Queries In cases where the active set is entirely generated and saved in a temporary table the database server can take quite some time to open the cursor After ward it can tell the program exactly how many rows the active set contains This information is not made available however One reason is that you can 5 24 Programming with SQL Retrieving Multiple Rows never be sure which method the optimizer uses If it can avoid sorts and temporary tables it does but very small changes in the query in the sizes of the tables or in the available indexes can change its methods The Active Set for a Sequential Cursor The database server wants to tie up as few resources as possible in maintaining the active set of a cursor If it can do so the database server never retains more than the single row that is fetched next It can do this for most sequential cursors On each fetch it returns the contents of the current row and locates the next one The Active Set for a Scroll Cursor All the rows in the active set for a scroll cursor must be retained until the cursor closes because the database server cannot be sure which row the program will ask for next Most frequently the database server implements the active set of a scroll cursor as a temporary table The database server might not fill this table immediately however unless it created a temporary table to process the query Usually it creates the temporary table when t
355. g and Using Stored Procedures Figure 14 4 Figure 14 5 The read_address procedure returns values therefore if you are executing a procedure from an SQL API or from another procedure you must use an INTO clause with host variables to receive the data For example executing the read_address procedure in an ESQL C program is accomplished with the code segment shown in Figure 14 4 include lt stdio h gt Sinclude sqlca Sinclude sqlda Sinclude datetime Program to execute a procedure in the database named play main char lname 16 fname 16 address 21 char city 16 state 3 zip 6 connect to play SEXECUTE PROCEDURE read_address Putnum INTO Slname fname Saddress city S state zip if sqlca sqlcode 0 printf nFailure on execute Executing a procedure using ESQL IC If you are executing a procedure within another procedure you can use the SPL statements CALL or LET to run the procedure To use the CALL statement with the read_address procedure you can use the code shown in Figure 14 5 CREATE PROCEDURE address_list DEFINE p_lname p_fname p_city CHAR 15 DEFINE p_add CHAR 20 DEFINE p_state CHAR 2 DEFINE p_zip CHAR 5 CALL read_address Putnum RETURNING p_fname p_lname p_add p_city p_state p_zip use the returned data some way END PROCEDURE Calling a procedure inside another procedure with the CALL statement Figure 14
356. g no change e Audit information that allows an erroneous update to be traced back to the transaction that entered the row It is usually much faster to insert a new row in an update journal than actually to perform the update on one or more base tables For one thing the journal has at most one index to update but the base tables usually have several For another locking delays are almost nil because inserting a row in a table with no indexes requires only a lock on the inserted row Another p rogram can insert its row even before the first program commits its transaction Also because no updates are performed on the primary tables their pages are not locked This allows query programs to run without delays After peak usage hours perhaps after close of business you run a batch program to validate and apply the updates row by row as they were inserted You obviously would want to take pains to see that no update is forgotten or applied twice regardless of possible system failures Tuning Your Data Model 10 33 Maximizing Concurrency One way to update the base table is to use two cursors The first cursor is a hold cursor it is used to scan the rows of the journal See Hold Cursors in Chapter 7 For each row of the journal the program goes through the following steps 1 Issue the BEGIN WORK statement 2 Fetch the rows from the tables being updated using an update cursor This locks only these rows 3 Val
357. g rules while you define the tables of a formal data model Rows must stand alone Each row of a table is independent and does not depend on any other row of the same table As a consequence the order of the rows in a table is not significant in the model The model should still be correct even if all the rows of a table are shuffled into random order After the database is implemented you can tell the database server to store rows in a certain order for the sake of efficiency but that does not affect the model 8 20 Building Your Data Model Translating E R Data Objects Into Relational Constructs Rows must be unique In every row some column must contain a unique value If no single column has this property the values of some group of columns taken as a whole must be different in every row e Columns must stand alone The order of columns within a table has no meaning in the model The model should still be correct even if the columns are rearranged After the database is implemented programs and stored queries that use an asterisk to mean all columns are dependent on the final order of columns but that does not affect the model Column values must be unitary A column can contain only single values never lists or repeating groups Composite values must be broken into separate columns For example if you decide to treat a person s first and last names as separate values as shown in the examples in this c
358. gative value returned ETURN 10 x END Breaking out of nested loop with a RAISE EXCEPTION statement Remember that a BEGIN END block is a single statement When an error occurs somewhere inside a block and the trap is outside the block when exe cution resumes the rest of the block is skipped and execution resumes at the next statement Unless you set a trap for this error somewhere in the block the error condition is passed back to the block that contains the call and back to any blocks that contain the block If no ON EXCEPTION statement exists that is set to handle the error execution of the procedure stops creating an error for the program or procedure that is executing the procedure Creating and Using Stored Procedures Summary Summary Stored procedures provide many opportunities for streamlining your database process including enhanced database performance simplified applications and limited or monitored access to data See the Informix Guide to SQL Syntax for syntax diagrams of SPL statements Creating and Using Stored Procedures 14 33 Summary 14 34 Creating and Using Stored Procedures Creating and Using Triggers Chapter Overview 3 When to Use Triggers 3 How to Create a Trigger 4 Assigning a Trigger Name 5 Specifying the Trigger Event 5 Defining the Triggered Actions 5 A Complete CREATE TRIGGER Statement 6 Using Triggered Actions 7 Using BEFORE and AFTER Triggered Actions 7 Using FOR
359. ging Indexes on page 10 19 However any user with Resource privileges can build additional indexes Use the CREATE INDEX statement to make an index An index consumes disk space proportional to the width of the key values and the number of rows See The Structure of an Index on page 13 20 Also the database server must update the index whenever rows are inserted deleted or updated this slows these operations If necessary you can use the DROP INDEX statement to release the index after a series of queries thus freeing space and making table updates easier 13 34 Optimizing Your Queries Making Queries Faster Using Unions to Avoid Sequential Access Certain forms of WHERE clauses force the optimizer to use sequential access even when indexes exist on all the tested columns The following query forces sequential access to the orders table SELECT FROM orders WHERE customer_num 104 AND order_num gt 1001 OR order_num 1008 The key element is that two or more separate sets of rows are retrieved The sets are defined by relational expressions that are connected by OR In the following example one set is selected by this test customer_num 104 AND order_num gt 1001 The other set is selected by the test shown in the following example order_num 1008 The optimizer uses a sequential access path even though indexes exist on the customer_num and order_num columns You can speed
360. gle Table SELECT Statements Using Variable Text Searches Figure 2 3 You can use the keywords LIKE and MATCHES for variable text queries based on substring searches of CHARACTER fields Include the keyword NOT to indicate the opposite condition The keyword LIKE is the ANSI standard whereas MATCHES is an Informix extension Variable text search strings can include the wildcards listed in Figure 2 3 with LIKE or MATCHES Symbol Meaning LIKE evaluates to zero or more characters a evaluates to a single character escapes special significance of next character MATCHES i evaluates to zero or more characters 2 evaluates to a single character except null evaluates to single character or range of values X escapes special significance of next character Wildcards used with LIKE and MATCHES You cannot test a TEXT or BYTE column with LIKE or MATCHES Using Exact Text Comparisons The following examples include a WHERE clause that searches for exact text comparisons by using the keyword LIKE or MATCHFS or the relational oper ator Unlike earlier examples these examples illustrate how to query on an external table in an ANSI compliant database An external table is a table that is not in the current database You can access only external tables that are part of an ANSI compliant database Whereas the database used previously in this chapter was the demonstration database called stores6 the FROM clause in the following
361. gn Keys Join Columns 24 Adding Keys to the Telephone Directory Diagram 25 Resolving Your Relationships 26 Resolving m n Relationships 26 Resolving Other Special Relationships 28 Normalizing Your Data Model 29 First Normal Form 29 Second Normal Form 31 Third Normal Form 32 Summary of Normalization Rules 32 Summary 33 8 2 Building Your Data Model Chapter Overview The first step in creating a database is to construct a data model a precise complete definition of the data to be stored This chapter contains a cursory overview of one method of doing this The following chapters describe how to implement a data model once you design it To understand the material in this chapter you should have a basic understanding of SQL and relational database theory Why Build a Data Model You may already have an idea of a database If you use some type of formal notation to build your data model you can help your design in two ways It makes you think through the data model completely A mental model often contains unexamined assumptions formalizing the design reveals these points e Itis easier to communicate your design to other people A formal statement makes the model explicit so that others can return comments and suggestions in the same form Entity Relationship Data Model Overview Different books present different formal methods of modeling data Most methods force you to be thorough and precise If you have alread
362. h instance of the identifier is a variable Qualify the column name with the table name to use the identifier Creating and Using Stored Procedures 14 19 Variables and Expressions as acolumn name In the following example the procedure variable Iname is the same as the column name In the following SELECT statement customer Iname is a column name and Iname is a variable name CREATE PROCEDURE table_test iw EFINE lname CHAR 15 LET lname Miller SELECT customer lname FROM customer INTO lname WHERE customer_num 502 Variables and SQL Functions If you use the same identifier for a procedural variable as for an SQL function the database server assumes that an instance of the identifier is a variable and disallows the use of the SOL function You cannot use the SQL function within the block of code in which the variable is defined The following example shows a block within a procedure in which the variable called user is defined This definition disallows the use of the USER function while in the BEGIN END block CREATE PROCEDURE user_test DEFINE name CHAR 10 DEFINE name2 CHAR 10 LET name user the SQL function BEGIN DEFINE user CHAR 15 disables user function LET user Miller LET name user assigns Miller to variable name END LET name2 user SQL function again 14 20 Creating and Using Stored Procedures Variables and Expressions Pro
363. h procedure calls compiler program Overview of processing a program with embedded SQL statements The converted source program then passes through the programming language compiler The compiler output becomes an executable program after it is linked with a library of SQL API procedures When the program runs the SQL API library procedures are called they set up communications with the database server to carry out the SQL operations Whereas SQL APIs products allow you to embed SQL in the host language some languages have SQL as a natural part of their statement set INFORMIX 4GL incorporates the SQL language as a natural part of the fourth generation language it supports Informix Stored Procedure Language SPL also uses SQL as a natural part of its statement set You use INFORMIX 4GL or an SQL API product to write application programs You use SPL to write procedures that are stored with a database and are called from an application program 5 4 Programming with SQL SQL in Programs Static Embedding You can introduce SQL statements into a program in two ways The simpler and more common way is by static embedding which means that the SQL statements are written as part of the source program text The statements are static because they are a fixed part of the source text Dynamic Statements Some applications require the ability to compose SQL statements in response to user input For example a program might have to select diffe
364. hapter they must be in separate columns not in a single name column e Each column must have a unique name Two columns within the same table cannot share the same name However you may have columns that contain similar information For example the name table in the telephone directory example contains col umns for children s names You can name each column child1 child2 and so on e Each column must contain data of a single type A column must contain information of the same data type For example a column identified as an integer must contain only numeric information not characters from a name If your previous experience is only with data organized as arrays or sequential files these rules might seem unnatural However relational data base theory shows that you can represent all types of data using only tables rows and columns that follow these rules With a little practice these rules become automatic Placing Constraints on Columns When you define your table and columns with the CREATE TABLE statement you constrain each column These constraints specify whether you want the column to contain characters or numbers the form that you want dates to Building Your Data Model 8 21 Translating E R Data Objects Into Relational Constructs use and other constraints A domain describes the constraints on and identifies the set of valid values attributes may assume The domain characteristics of a column can consist
365. hat creates a conflict Thousands of Informix customers have embedded Informix style SQL in programs and stored queries They rely on Informix to keep its language the same Other customers require the ability to use databases in a way that conforms exactly to the ANSI standard They rely on Informix to change its language to conform Informix resolved the conflict with the following compromise The Informix version of SQL with its extensions to the standard is avail able by default e You can ask any Informix SQL language processor to check your use of SQL and post a warning flag whenever you use an Informix extension This resolution is fair but makes the SQL documentation more complicated Wherever a difference exists between Informix and ANSI SQL the Informix Guide to SOL Syntax describes both versions Because you probably intend to use only one version you will have to ignore the version you do not need ANSI Compliant Databases You can designate a database as ANSI compliant by using the MODE ANSI keywords when you create it Within such a database certain characteristics of the ANSI standard apply For example all actions that modify data auto matically take place within a transaction which means that the changes are made in their entirety or not at all Differences in the behavior of ANSI compliant databases are noted where appropriate in the Informix Guide to SQL Syntax Introducing Database Features and SQL 1 15
366. hat the ship_instruct ship_weight and ship_charge columns are queried only in one program In that case you can move them out to a companion table 10 28 Tuning Your Data Model Denormalizing Division by Frequency of Update Updates take longer than queries and the updating programs lock index pages and rows of data slowing down the programs that only query If cer tain attributes of an entity are updated frequently and many others are changed only rarely or not at all and if many queries select the latter and do not need the former you can split the volatile columns to a companion table The updating programs contend for the use of that table and the query programs use the primary table Costs of Companion Tables Splitting a table consumes extra disk space and adds complexity Two copies of the primary key occurs for each row one copy in each table Two primary key indexes also exist You can use the methods described in earlier sections to estimate the number of pages added You must modify existing programs reports and forms that use SELECT because fewer columns are returned Programs reports and forms that use attributes from both tables must perform a join to bring them together In this case when you insert or delete a row two tables are altered instead of one If you do not coordinate the alteration of the two tables by making them within a single transaction for example you lose semantic integrity Sp
367. he cursor is opened Then the first time a row is fetched the database server copies it into the tem porary table and returns it to the program When a row is fetched for a second time it can be taken from the temporary table This scheme uses the fewest resources in the event that the program abandons the query before it fetches all the rows Rows that are never fetched are not created or saved The Active Set and Concurrency When only one program is using a database the members of the active set cannot change This is the situation in most desktop workstations and it is the easiest situation to think about But some programs must be designed for use in a multiprogramming system where two three or dozens of different programs can work on the same tables simultaneously When other programs can update the tables while your cursor is open the idea of the active set becomes less useful Your program can see only one row of data at a time but all other rows in the table can be changing In the case of a simple query when the database server holds only one row of the active set any other row can change The instant after your program fetches a row another program can delete the same row or update it so that if it is examined again it is no longer part of the active set Programming with SQL 5 25 Retrieving Multiple Rows When the active set or part of it is saved in a temporary table stale data can present a problem That is
368. he duration column of the view cannot be updated because it represents an expression the database server cannot even in principle decide how to dis tribute an update value between the two columns named in the expression But as long as no derived columns are named in the SET clause the update can be performed as if the view were a table A view can return duplicate rows even though the rows of the underlying table are unique You cannot distinguish one duplicate row from another If you update one of a set of duplicate rows for example by using a cursor to update WHERE CURRENT you cannot be sure which row in the underlying table receives the update Inserting into a View You can insert rows into a view provided that the view is modifiable and contains no derived columns The reason for the second restriction is that an inserted row must provide values for all columns and the database server cannot tell how to distribute an inserted value through an expression An attempt to insert into the call_response view shown in Figure 11 8 would fail When a modifiable view contains no derived columns you can insert into it as if it were a table However the database server uses null as the value for any column that is not exposed by the view If such a column does not allow nulls an error occurs and the insert fails Using WITH CHECK OPTION It is possible to insert into a view a row that does not satisfy the conditions of the view tha
369. he procedure select the data column from the sysprocbody system catalog table The following SELECT statement reads the read_address procedure text SELECT data FROM informix sysprocbody WHERE datakey T find text lines AND procid SELECT procid FROM informix sysprocedures WHERE informix sysprocedures procname read_address Looking at the Procedure Documentation If you want to view only the documenting text of the procedure use the fol lowing SELECT statement to read the documentation string The documenta tion lines found in the following example are those in the DOCUMENT clause of the CREATE PROCEDURE statement SELECT data FROM informix sysprocbody WHERE datakey D find documentation lines AND procid SELECT procid FROM informix sysprocedures WHERE informix sysprocedures procname read_address Executing a Procedure You can execute a procedure in several ways You can use the SQL statement EXECUTE PROCEDURE or either the LET or CALL SPL statement In addition you can dynamically execute procedures as described in the section Executing a Stored Procedure Dynamically on page 14 11 The read_address procedure returns the fullname and address of a customer To run read_address on a customer called Putnum using EXECUTE PROCEDURE enter the following statement EXECUTE PROCEDURE read_address Putnum Creating and Using Stored Procedures 14 9 Creatin
370. he select list requested every column You also can create an equi join with additional constraints one where the comparison condition is based on the inequality of values in the joined col umns These joins use a relational operator other than in the comparison condition specified in the WHERE clause When columns in the joined tables have the same name the columns must be preceded by the name of a specific table and a period as shown in Query 2 73 SELECT order_num order_date ship_date cust_calls FROM orders cust_calls WHERE call_dtime gt ship_date AND cust_calls customer_num orders customer_num ORDER BY customer_num Query 2 73 Composing Simple SELECT Statements 2 73 Multiple Table SELECT Statements Query 2 73 joins on the customer_num column and then selects only those rows where the call_dtime in the cust_calls table is greater than or equal to the ship_date in the orders table It returns the rows shown in Query Result 2 73 order_num order_date 0 ship_date 0 customer_num call_dtime 004 5 22 1993 5 30 1993 06 993 06 12 08 20 user_id mary call_code D call_descr Order received okay but two of the cans of res_dtime res_descr i E order_num order_date 0 ship_date 0 customer_num call_dtime user_id Hes call_code L call_descr O res_dtime res_descr Cc Y N order_num order_date 0 ship_date 0 customer_num call_dtime user_id m call_code I call_descr R
371. he table The stock table has col umns for the following facts about items of merchandise stock numbers manufacturer codes descriptions prices and units of measure Each row of a table stands for one instance of the subject of the table which is one particular example of that entity Each row of the stock table stands for one item of merchandise that is sold by the sporting goods store Tables Rows and Columns You now understand that the relational model of data is a very simple way of organizing data to reflect the world using the following simple correspond ing relationships table entity A table represents all that the database knows about one subject or kind of thing column attribute A column represents one feature characteristic or fact that is true of the table subject row instance A row represents one individual instance of the table subject Some rules apply about how you choose entities and attributes but they are important only when you are designing a new database Database design is covered in Chapters 8 through 11 The data model in an existing database already is set To use the database you need to know only the names of the tables and columns and how they correspond to the real world 1 12 Introducing Database Features and SQL Important Database Terms Operations on Tables Because a database is really a collection of tables database operations are operations on tables The relational mo
372. hem automatically Informix offers the SERIAL data type for serial numbers However the people who use the database might not like a plain numeric code Other codes can be based on actual data for example an employee identification code could be based on the person s initials com bined with the digits of the date they were hired In the telephone directory example a system assigned primary key is used for the name table Foreign Keys Join Columns Figure 8 11 A foreign key is simply a column or group of columns in one table that contains values that match the primary key in another table Foreign keys are used to join tables in fact most of the join columns referred to earlier in this book are foreign key columns Figure 8 11 shows the primary and foreign keys of the customer and order tables from the stores6 database customer orders customer_num order_num customer_num lt primary key foreign key Primary foreign keys in the customer order relationships Foreign keys are noted wherever they appear in the model because their presence can restrict your ability to delete rows from tables Before you can delete a row safely either you must delete all rows that refer to it through foreign keys or you must define the relationship using special syntax that allows you to delete rows from primary key and foreign key columns with a single delete command The database server disallows dele
373. hen errors occur If information is correctly inserted into the database no rows are returned Set Operations The standard set operations union intersection and difference let you manipulate database information These three operations enable you to use SELECT statements to check the integrity of your database after you perform an update insert or delete They can be useful when you transfer data to a history table for example and want to verify that the correct data is in the history table before you delete it from the original table 3 42 Composing Advanced SELECT Statements Union Set Operations The union operation uses the UNION keyword or operator to combine two queries into a single compound query You can use the UNION keyword between two or more SELECT statements to unite them and produce a tempo rary table containing rows that exist in any or all of the original tables Note that you cannot use a UNION operator inside a subquery or in the definition of a view Figure 3 1 illustrates the union set operation SELECT DISTINCT stock_num manu_code FROM stock WHERE unit_price lt 25 00 F quantity UNION SELECT stock_num manu_code preter Taa than unit_price lt 25 00 EROM items than 3 or equal to3 less than Ae ara 25 00 qualifies qualifies unit_price greater than os or equal to qualifies 25 00 Figure 3 1 The union set operation The UNION keyword selects all row
374. his means that rows sorted on a SERIAL column are returned in the order in which they were created That cannot be said of any other data type You can specify the initial value in a SERIAL column in the CREATE TABLE statement This makes it possible to generate different subsequences of system assigned keys in different tables The stores6 database uses this tech nique In stores6 the customer numbers begin at 101 and the order numbers start at 1001 As long as this small business does not register more than 899 customers all customer numbers have three digits and order numbers have four A SERIAL column is not automatically a unique column If you want to be perfectly sure no duplicate serial numbers occur you must apply a unique constraint see Using CREATE TABLE on page 9 24 However if you define the table using the interactive schema editor in DB Access or INFORMIX SQL it automatically applies a unique constraint to any SERIAL column The SERIAL data type has the following advantages It provides a convenient way to generate system assigned keys Itproduces unique numeric codes even when multiple users are updating the table e Different tables can use different ranges of numbers It has the following disadvantages Only one SERIAL column is permitted in a table Itcan produce only arbitrary numbers then again arbitrary numeric codes might not be acceptable to the database users 9 8 Implementing You
375. hiving a database with audit trails 1 292S manipulating audit trail file 1 293S syntax 1 2925 Recursion in a stored procedure 14 24T Recursive relationship 8 11T 8 28T Redundant data introduced for performance 10 31T Redundant relationship 8 29T REFERENCES FOR keywords in INFO statement 1 243S REFERENCES keyword in ALTER TABLE 1 215 in CREATE TABLE 1 948 1 96S syntax in GRANT 1 235S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 302S References privilege definition of 1 236S displaying with the INFO statement 1 243S REFERENCING clause DELETE REFERENCING clause 1 119S INSERT REFERENCING clause 1 118S UPDATE REFERENCING clause 1 120S Index 35 using referencing 1 1255 15 9T Referential constraint and a DELETE trigger 1 1125 data type restrictions 1 965 definition of 1 215 1 945 4 19T dropping 1 32S enforcing 1 86S modifying a column with 1 285 rules of use 1 945 Referential integrity 4 19T defining primary and foreign keys 8 24T Regular expression effect on performance 13 32T evaluating with NLS 1 15R Relational calculus See also relational model Relational database defined 1 11T Relational model attribute 8 14T denormalizing 10 26T description of 1 11T 8 3T to 8 33T entity 8 4T join 2 8T many to many relationship 8 11T normalizing data 8 29T one to many relationship 8 11T one to one relationship 8 11T projection 2 6T resolving relationships 8 26T rules for defining tables rows and columns 8
376. hone num ber turns out to consist of three categories each with different features Building Your Data Model 8 5 Identifying and Defining Your Principal Data Objects These choices are neither simple nor automatic To discover the best choice of entities you must think deeply about the nature of the data you want to store Of course that is exactly the point of making a formal data model The following section describes the example shown in this chapter in further detail The Telephone Directory Example Suppose that you create a database that computerizes a personal telephone directory The database model must record the names addresses and telephone numbers of people and organizations that its user deals with for business and pleasure The first step is to define the entities and the first thing you might do is look carefully at a page from a telephone directory to see what entities are there PHONE NAME PHONE 503 776 3428 o jv Catherine Morgan 206 789 5396 7 E ADDRESS Q i w 429 Bridge Way Seattle WA 98103 NAME PHONE e Norman Dearborn 206 598 818 ADDRESS 1 l Morganthaler Industries 12558 E 10th Ave Seattle WA O 9 98102 FAX 206 598 6872 Thomas Morrison 503 256 6031 ADDRESS ne O i YV 866 Gage Rd Klamath Falls OR 97601 Figure 8 1 Part of a page from a telephone directory 8 6 Bu
377. icate rows from query results Sort retrieved data with the ORDER BY clause and the DESC keyword Select and order data containing foreign characters Use the BETWEEN IN MATCHES and LIKE keywords and various rela tional operators in the WHERE clause to create a comparison condition Create comparison conditions that include values exclude values find a range of values with keywords relational operators and subscripting and find a subset of values Perform variable text searches using exact text comparisons variable length wildcards and restricted and unrestricted wildcards Use the logical operators AND OR and NOT to connect search conditions or Boolean expressions in a WHERE clause Use the ESCAPE keyword to protect special characters in a query Search for null values with the IS NULL and IS NOT NULL keywords in the WHERE clause Use arithmetic operators in the SELECT clause to perform computations on number fields and display derived data Use substrings and subscripting to tailor your queries Assign display labels to computed columns as a formatting tool for reports Use the aggregate functions COUNT AVG MAX MIN and SUM in the SELECT clause to calculate and retrieve specific data Include the time functions DATE DAY MDY MONTH WEEKDAY YEAR CURRENT and EXTEND plus the TODAY LENGTH and USER functions in your SELECT statements Include stored procedures in your SELECT statements 2 84 Composing S
378. id value The use of rowid in a SELECT statement is discussed in Chapter 3 Composing Advanced SELECT Statements A rowid value specifies the physical location of the row and its page The database server simply reads the page incurring the costs already noted The Cost of Indexed Access An additional cost is associated with finding a row through an index The index itself is stored on disk and its pages must be read into memory The database server uses indexes in two ways One way is to look up a row given a key value This is the kind of look up used when you join two tables as shown in the following statement SELECT company order_num FROM customer orders WHERE customer customer_num orders customer_num One table probably customer is read sequentially Its value of customer_num is used to search the index on the customer_num column of orders When a match is found that row of orders is read An index look up works down from the root page to a leaf page See The Structure of an Index on page 13 20 The root page because it is used so often is almost always found in a page buffer The odds of finding a leaf page in a buffer depend on the size of the index the odds become poorer as the size of the table increases 13 18 Optimizing Your Queries Time Costs of a Query If a table is very large so that the number of index leaf pages is much larger than the buffer space almost every search causes a l
379. idate the update information from the journal against the data in the target rows 4 Apply the updates to the target tables Update the journal row in some way to mark it as finished Issue the COMMIT WORK statement or the ROLLBACK WORK statement if an error is found You run a different program to drop and re create the journal table only after every journal row is validated applied and marked The obvious disadvantage of an update journal is that the base tables do not reflect the most current data If it is essential that updates be instantly visible the journal scheme does not work The great advantages of reduced I O and reduced locking delays during peak hours are a powerful argument in favor of an update journal Deferred updates are accepted in many applications For example no bank promises to know your account balance more precisely than as of the close of business the preceding day and for exactly this reason the bank records transactions in a journal during the day and applies the updates overnight 10 34 Tuning Your Data Model Maximizing Concurrency Isolating and Dispersing Updates If updates really must be performed interactively during peak hours you must find a different way to isolate queries from updates Splitting Tables to Isolate Volatile Columns This idea was covered in an earlier section If it is necessary to perform updates during peak hours examine the structure of the tables Can you sep
380. ies the Informix client server product that you use and or to a textbook on computer networks Database Management System Configurations A relational database management system RDBMS includes all of the components necessary to create and maintain a relational database An Infor mix RDBMS has several pieces the user interface the database server and the data itself It is easiest to think of these pieces as all being located in the same computer but many other arrangements are possible In some arrangements the application and the database server are on different computers and the data is distributed across several others The client applications of an RDBMS do not need to be modified to run on a network The communications tools handle the tasks of locating and attach ing to the database servers To the application a database on a networked computer appears no different than a database on the computer where the application resides A Single User Configuration Figure 12 1 shows a diagram of a simple database management system on a single computer The organization in Figure 12 1 is one you would typically find on a personal computer running the DOS operating system It is unusual to have a single user situation on a UNIX system but you certainly can One example of a single user UNIX system would be a desktop workstation in a development environment 12 4 Understanding Informix Networking Database Management System Configurations
381. igure 8 5 on page 8 14 Verify for yourself that the relationships are the same in both figures 8 18 Building Your Data Model Diagramming Your Data Objects A matrix such as Figure 8 5 is a useful tool when you are first designing your model because in filling it out you are forced to think of every possible rela tionship However the same relationships appear in a diagram such as Figure 8 10 and this type of diagram may be easier to read when you are reviewing an existing model name Iname fname bdate address anniv street email city child1 state child2 PO OH zipcode child3 y Q voice Q fax Q modem vce_num fax_num mdm_num vce_type operfrom b300 opertill b1200 b2400 Figure 8 10 Preliminary entity relationship diagram of the Telephone Directory Example What s Next Subsequent sections describe the following tasks e How to translate the entities relationships and attributes into relational constructs e How to resolve the entity relationship data model e How to normalize the entity relationship data model Chapter 9 Implementing Your Data Model shows you how to create a database from the entity relationship data model Building Your Data Model 8 19 Translating E R Data Objects Into Relational Constructs Translating E R Data Objects Into Relational Constructs All the data objects you have learned about so far entities relationships a
382. igure 12 4 An example of local loopback Advantages and Disadvantages of Local Loopback Local loopback allows you to test network operations without requiring an actual remote machine but it is not as fast as a local IPC connection How ever unlike IPC shared memory communication local loopback is not vul nerable to corruption due to memory addressing errors or overindexed data arrays See Advantages and Disadvantages of Local Multiuser Systems on page 12 7 Distributed Databases Although a network lets you separate the application from the data the application still is limited to the contents of a single database With most database servers you only can query or modify tables in the current database A distributed database has information on multiple databases organized so that it appears as a single database to the user The data can be maintained by a variety of database servers and located on computers supported by different operating systems and communication networks 12 10 Understanding Informix Networking Database Management System Configurations The INFORMIX OnLine Dynamic Server database server allows you to query data in multiple databases anywhere on the network When the INFORMIX TP XA feature is added to INFORMIX OnLine Dynamic Server you can create global transactions that span multiple computer systems and even multiple XA compliant database systems from different vendors INFORMIX SE does not provide
383. ilding Your Data Model Identifying and Defining Your Principal Data Objects The physical form of the existing data can be misleading Do not let the layout of pages and entries in the telephone directory mislead you into trying to specify an entity that represents one entry in the bobok some kind of alpha betized record with fields for name number and address Remember it is not the medium you want to model it is the data At first glance the entities recorded in a telephone directory include the following items e Names of persons and organizations e Addresses Telephone numbers Do these entities meet the earlier criteria They are clearly significant to the model and are generic Are they fundamental A good test is to ask if an entity can vary in number independently of any other entity After thinking about it you realize that a telephone directory sometimes lists people who have no number or current address people who move or change jobs A telephone directory also can list both addresses and numbers that are used by more than one person All three of these entities can vary in number independently that strongly suggests they are fundamental not dependent Are they unitary Names can be split into personal names and corporate names After thinking about it you decide that all names should have the same features in this model that is you do not plan to record different infor mation about a company than you wou
384. imple SELECT Statements Summary This chapter also introduced simple join conditions that enable you to select and display data from two or more tables The section Multiple Table SELECT Statements described how to perform the following actions Create a Cartesian product e Constrain a Cartesian product by including a WHERE clause with a valid join condition in your query Define and create a natural join and an equi join Join two or more tables on one or more columns e Use aliases as a shortcut in multiple table queries Retrieve selected data into a separate temporary table with the INTO TEMP clause to perform computations outside the database The next chapter explains more complex queries and subqueries self joins and outer joins the GROUP BY and HAVING clauses and the UNION INTERSECTION and DIFFERENCE set operations Composing Simple SELECT Statements 2 85 Summary 2 86 Composing Simple SELECT Statements Chapter Composing Advanced SELECT Statements Chapter Overview 3 Using the GROUP BY and HAVING Clauses 4 Using the GROUP BY Clause 4 Using the HAVING Clause 9 Creating Advanced Joins 11 Self Joins 11 Outer Joins 21 Simple Join 22 Simple Outer Join on Two Tables 24 Outer Join for a Simple Join to a Third Table 26 Outer Join for an Outer Join to a Third Table 28 Outer Join of Two Tables to a Third Table 30 Subqueries in SELECT Statements 32 Using ALL 33 Using ANY 34 Single
385. impractical 1456 rows as shown in Query Result 2 71 customer_num fname lname company addressl address2 city state zipcode phone code sname customer_num fname lname company addressl address2 city state zipcode phone code sname customer_num fname lname company addressl address2 city state zipcode phone code sname Query Result 2 71 2 70 Composing Simple SELECT Statements 101 Ludwig Pauli All Sports Supplies 213 Erstwild Court Sunnyvale CA 94086 408 789 8075 AK Alaska 101 Ludwig Pauli All Sports Supplies 213 Erstwild Court Sunnyvale CA 94086 408 789 8075 HI Hawaii 101 Ludwig Pauli All Sports Supplies 213 Erstwild Court Sunnyvale CA 94086 408 789 8075 CA California Multiple Table SELECT Statements Note that some of the data displayed in the concatenated rows is inaccurate For example although the city and state from the customer table indicate an address in California the code and sname from the state table might be for a different state Creating a Join Equi Join Conceptually the first stage of any join is the creation of a Cartesian product To refine or constrain this Cartesian product and eliminate meaningless rows of data include a WHERE clause with a valid join condition in your SELECT statement This section illustrates equi joins natural joins and multiple table joins Additional complex forms such as self joins and outer jo
386. in INFORMIX OnLine Dynamic Server as an enhancement to referential integrity Previously when you attempted to delete a row from a parent table without deleting rows from associated child tables first the delete was disallowed Now you can specify the ON DELETE CASCADE option on either the CREATE TABLE or ALTER TABLE statements or on DB Access menus to allow deletes from a parent table to cause deletes on child tables New Features in Informix Version 6 0 Products That Use SQL Enhanced CREATE INDEX statement You can now use the FILLFACTOR option on the CREATE INDEX statement to create indexes that provide for expansion of the index at a later time or to create compacted indexes Enhanced Arithmetic Functions You can now use certain trigonometric and algebraic functions in your SQL statements The new functions include ABS MOD POW ROOT SQRT COS SIN TAN ACOS ASIN ATAN ATAN2 EXP LOGN and LOG10 Enhanced Error Handling You can now use a new statement to retrieve standard and multiple diagnostic information about your SQL statements The GET DIAGNOS TICS statement is compliant with X Open and ANSI ISO specifications and provides a standard method for detecting and handling error messages The GET DIAGNOSTICS statement is used with a new error handling status variable called SQLSTATE New DBINFO Function The DBINFO function allows you to find the following information o The dbspace name for a given table o The last se
387. in a SELECT statement An alias is a word that immediately follows the name of a table in the FROM clause You can use it wherever the table name would be used for instance as a prefix to the column names in the other clauses SELI ECT s stock_num s manu_code s description s unit_price s unit c catalog_num c cat_descr c cat_advert m lead_time FROM stock s catalog c manufact m WHERE s stock_num c stock_num AND s manu_code c manu_code AND s manu_code m manu_code AND s manu_code IN HRO HSK AND s stock_num BETWEEN 100 AND 301 ORDER BY catalog_num Query 2 78a Composing Simple SELECT Statements 2 79 Multiple Table SELECT Statements The associative nature of the SELECT statement allows you to use an alias before you define it In Query 2 78a the aliases s for the stock table c for the catalog table and m for the manufact table are specified in the FROM clause and used throughout the SELECT and WHERE clauses as column prefixes Compare the length of Query 2 78a with Query 2 78b which does not use aliases SELECT stock stock_num stock manu_code stock description stock unit_price stock unit catalog catalog_num catalog cat_descr catalog cat_advert manufact lead_time FROM stock catalog manufact WHERE stock stock_num catalog stock_num AND stock manu_code catalog manu_code AND stock manu_code manufact manu_code AND stock manu_code IN HRO HSK AND stock stock_n
388. in one or more existing rows of a table This statement takes two fundamentally different forms One lets you assign specific values to col umns by name the other lets you assign a list of values that might be returned by a SELECT statement to a list of columns In either case if you are Modifying Data 4 11 Statements That Modify Data updating rows and some of the columns have data integrity constraints the data you change must be within the constraints placed on those columns For more information refer to Database Privileges on page 4 15 Selecting Rows to Update Either form of the UPDATE statement can end with a WHERE clause that determines which rows are modified If you omit it all rows are modified The WHERE clause can be quite complicated to select the precise set of rows that need changing The only restriction on it is that the table that you are updating cannot be named in the FROM clause of a subquery The first form of an UPDATE statement uses a series of assignment clauses to specify new column values as shown in the following example UPDATE customer SET fname Barnaby lname Dorfler WHERE customer_num 103 The WHERE clause selects the row to be updated In the stores6 database the customer customer_num column is the primary key for that table so this statement can update no more than one row You can also use subqueries in the WHERE clause Suppose that the Anza Corporation issues a
389. indexes and maximizing concurrency e Chapter 11 Granting and Limiting Access to Your Database details how you can ensure data security by granting privileges and using stored procedures and views e Chapter 12 Understanding Informix Networking discusses networks and how you can best set up a database to work over a network Part III Using Advanced SQL This part contains advanced SQL chapters such as how to optimize your queries how to create and use stored proce dures and how to create and use triggers Read these chapters if you need better performance in your database Chapter 13 Optimizing Your Queries defines techniques to refine and optimize your queries introduces and explains the query Optimizer and discusses the time costs of various operations e Chapter 14 Creating and Using Stored Procedures describes how to create and use stored procedures Chapter 15 Creating and Using Triggers describes how to create and use triggers Informix Welcomes Your Comments A reader response card is provided with this manual Please use this card to tell us what you like or dislike about this manual To help us with future ver sions of the manual please tell us about any corrections or clarifications that you would find useful Return this card to Informix Software Inc Technical Publications Department 4100 Bohannon Drive Menlo Park CA 94025 If you prefer to share your com
390. ing Single Rows 5 13 Data Type Conversion 5 14 Dealing with Null Data 5 15 Dealing with Errors 5 16 Retrieving Multiple Rows 5 19 Declaring a Cursor 5 20 Opening a Cursor 5 20 Fetching Rows 5 21 Cursor Input Modes 5 23 The Active Set of a Cursor 5 24 Using a Cursor A Parts Explosion 5 26 Dynamic SQL 5 28 Preparing a Statement 5 29 Executing Prepared SQL 5 31 Dynamic Host Variables 5 33 Freeing Prepared Statements 5 33 Quick Execution 5 34 Embedding Data Definition Statements 5 34 Embedding Grant and Revoke Privileges 5 34 Summary 5 37 Modifying Data Through SQL Programs Chapter Overview 6 3 Using DELETE 6 3 Direct Deletions 6 4 Deleting with a Cursor 6 7 Using INSERT 6 8 Using an Insert Cursor 6 8 Rows of Constants 6 11 An Insert Example 6 12 Using UPDATE 6 14 Using an Update Cursor 6 15 Cleaning up a Table 6 16 Summary 6 17 Programming for a Multiuser Environment Chapter Overview 7 3 Concurrency and Performance 7 3 Locking and Integrity 7 3 Locking and Performance 7 3 Concurrency Issues 7 4 How Locks Work 7 5 Kinds of Locks 7 6 Lock Scope 7 6 The Duration of a Lock 7 8 Locks While Modifying 7 9 Setting the Isolation Level 7 9 Dirty Read Isolation 7 10 Committed Read Isolation 7 10 Cursor Stability Isolation 7 11 Repeatable Read Isolation 7 12 Setting the Lock Mode 7 13 Waiting for Locks 7 13 Not Waiting for Locks 7 14 Waiting a Limited Time 7 14 Handling a Deadlock 7 14 Handling External Dead
391. ing a statement the database server determines whether the user has the necessary privileges The information is in the system catalog see Privileges in the System Catalog on page 11 9 The database server looks first for privileges granted specifically to the requesting user If it finds such a grant it uses that information It then checks to see if less restrictive privileges have been granted to PUBLIC If so the database server uses the less restrictive privileges If there has been no grant to that user the database server looks for privileges granted to public If it finds a relevant one it uses that Thus you can set a minimum level of privilege for all users by granting privileges to public You can override that in specific cases by granting higher individual privileges to users The Connect privilege is necessary before users can access a database Ordinarily in a database that does not contain highly sensitive or private data you give the GRANT CONNECT TO PUBLIC privilege shortly after reating the database If you do not grant the Connect privilege to public the only users who can access the database through the database server are those to whom you spe cifically grant the Connect privilege If limited users should have access this is your means of providing it to them and denying it to all others 11 6 Granting and Limiting Access to Your Database Granting Privileges Resource Privilege The Resource pri
392. ing any computer performance problem Follow the procedure to help avoid over looking possible solutions including the nontechnical ones that sometimes provide the best answer to performance problems Verifying the Problem Before you begin optimizing SQL statements be sure the problem lies with the program How much more effective can the user be if you make the program faster If the answer is not much look elsewhere for a solution 13 4 Optimizing Your Queries Optimizing Techniques Considering the Total System Consider the entire system of programs computers and users within an organization You might find a better solution by changing schedules or man aging resources differently If you are using INFORMIX OnLine Dynamic Server you might want to make sure that your system is tuned for efficiency Maybe the problem operation would be faster if it were done at a different time on a different machine or with different jobs running at the same time or maybe not But you need to consider these possibilities before you decide the best solution For information on tuning your INFORMIX OnLine Dynamic Server system see the INFORMIX OnLine Dynamic Server Administrator s Guide Understanding the Application Learn all about the application as a whole A database application usually has many parts such as saved queries screen forms report specifications and programs Consider them together with the user s procedures
393. ing paragraphs For the cat_descr column the text of a description is at most a double spaced page which is 250 words or approximately 1 500 characters so typage 1 A description exists for every entry so nnpart 1 0 Thus totpage 1 x 5 000 x 1 0 5 000 pages of data The cat_picture column contains line art in a computer readable form Examining several of these pictures reveals that they vary widely in size but a typical file contains about 75 000 bytes of data Thus typage 38 The marketing department estimates that they want to store a picture with one entry in four nnpart 0 25 Therefore totpage 38 x 5 000 x 0 25 47 500 pages of data After a table is built and loaded you can check the use of blobpages with the oncheck utility ptT option Locating Blob Data When you create a BYTE or TEXT column on magnetic disk you have the option of locating the data of the column in the tblspace or in a blobspace You can also store blob data on optical media although this discussion does not apply to blobs stored in this way In the following example a TEXT value is located in the tblspace and a BYTE value is located in a blobspace named rasters CREATE TABLE examptab pic_id SERIAL pic_desc TEXT IN TABLE pic_raster BYTE IN rasters A TEXT or BYTE value is always stored apart from the rows of the table Only a 56 byte descriptor is stored with the row However the value itself occupies a
394. ing two tables to a third three to a fourth and so on Optimizing Your Queries 13 11 The Query Optimizer The optimizer adds any final work to the completed join plans For example if the query contains an ORDER BY or GROUP BY clause and a plan does not produce rows in ordered sequence the optimizer adds to the plan an estimate of the cost of sorting the output Sorting is discussed in Time Cost of a Sort on page 13 15 Finally the optimizer selects a plan that appears to promise the least amount of work and passes it to the main part of the database server to be executed Reading the Plan The choice the optimizer makes does not have to remain a mystery you can determine exactly what query plan it chooses Execute the statement SET EXPLAIN ON before you execute a query Beginning with the next query the optimizer writes an explanation of its query plan to a particular file the name of the file and its location depend on the operating system in use A typical explanation is shown in Figure 13 1 After repeating the query the optimizer shows its estimate of the work to be done 102 in Figure 13 1 in arbitrary units A single disk access is one unit and other actions are scaled to that This query plan was chosen over others because the estimated cost for its execution was the lowest among all the plans considered 13 12 Optimizing Your Queries Figure 13 1 The Query Optimizer QUERY SELECT C custom
395. inition of that structure is not within the file it is in the programs that create or use the file For exam ple a document file as stored by a word processing program may contain very detailed structures describing the format of the document However only the word processing program can decipher the contents of the file because the structure is defined within the program not within the file A data model however is contained in the database it describes It travels with the database and is available to any program that uses the database The model defines not only the names of the data items but also their data types so a program can adapt itself to the database For example a program can find out that in the current database a price item is a decimal number with eight digits two to the right of the decimal point then it can allocate storage for a number of that type How programs work with databases is the subject of Chapter 5 Programming with SQL and Chapter 6 Modifying Data Through SQL Programs Querying Data Another difference between a database and a file is the way you can interrogate them You can search a file sequentially looking for particular val ues at particular physical locations in each line or record That is you might ask a file What records have numbers under 20 in the fifth field Figure 1 2 illustrates this type of search 1 6 Introducing Database Features and SQL Figure 1 2 Databases
396. ins are covered in Chapter 3 Composing Advanced SELECT Statements An equi join is a join based on equality or matching values This equality is indicated with an equal sign in the comparison operation in the WHERE clause as shown in Query 2 72 SELECT FROM manufact stock WHERE manufact manu_code stock manu_code Query 2 72 Composing Simple SELECT Statements 2 71 Multiple Table SELECT Statements Query 2 72 joins the manufact and stock tables on the manu_code column retrieving only those rows for which the values for the two columns are equal as shown in Query Result 2 72 manu_code SMT manu_name Smith lead_time 3 stock_num 1 manu_code SMT description baseball gloves unit_price 450 00 unit case unit_descr 10 gloves case manu_code SMT manu_name Smith lead_time S stock_num 5 manu_code SMT description tennis racquet unit_price 25 00 unit each unit_descr each manu_code SMT manu_name Smith lead_time 3 stock_num 6 manu_code SMT description tennis ball unit_price 36 00 unit case unit_descr 24 cans case manu_code ANZ manu_name Anza lead_time 5 stock_num 5 manu_code ANZ description tennis racquet unit_price 19 80 unit each unit_descr each Query Result 2 72 2 72 Composing Simple SELECT Statements Multiple Table SELECT Statements Note that in this equi join Query Result 2 72 includes the manu_code column from both the manufact and stock tables because t
397. ion must have an entry in the INFORMIXDIR etc sqlhosts file and corresponding entries in the etc hosts and etc services files These files are described in detail in the INFORMIX OnLine Dynamic Server Administrator s Guide and INFORMIX SE Administrator s Guide etc hosts INFORMIXDIR etc sqlhosts address of serverA serverA serverB serverC Pe etc services protocol for serverA Figure 12 7 Connectivity Information for Networks Understanding Informix Networking 12 15 Accessing Tables SQL Connection Statements Before it can do anything else the client application must open a database by executing a CONNECT statement or a DATABASE statement The CONNECT statement is preferred because it conforms with both ANSI and X Open standards that attempt to specify uniform syntax for networked and non networked environments Here is an example of the CONNECT statement CONNECT TO databasename servernam If the servername is omitted from the statement the application connects to the default database server specified by the INFORMIXSERVER environment variable If the databasename is omitted the application connects to the database server servername but does not open a database Before you can use a database you must issue a DATABASE CREATE DATABASE or START DATABASE statement Notice that the CONNECT statement does not give any information about the location of the database server
398. ion the opportunity to access data from several computers Response from a database server using network communication is not as fast as response from a database server using local IPC communication because of the extra computing required to prepare the data for network communica tion and because of the transmit time A network is somewhat more difficult to configure and maintain than a local system that uses IPC communication Single Machine Configuration Using Network Communication Figure 12 4 shows a configuration that behaves as if there were multiple sites residing on one machine In this configuration which is known as local loop back all the components are on the same computer but the connections are made as if they were connected through a network Because the connections use network software the database server appears to the application as a remote site The dashed line indicates the division between the two sites The database administrator configures the system to provide local or local loopback connections or both The software for the client application and the software for the database server can be stored in the same directory or the software can be stored in two separate directories Understanding Informix Networking 12 9 Database Management System Configurations Be computer server site application B 0o databases network 1 database connection server F
399. ions that either must be accomplished completely or not at all The database server guarantees that operations per formed within the bounds of a transaction are either completely and perfectly committed to disk or the database is restored to the state it was in before the transaction started The transaction is not merely protection against unforeseen failures it also offers a program a way to escape when the program detects a logical error This is discussed further in Chapter 6 Modifying Data Through SQL Programs Modifying Data 4 23 Interrupted Modifications Transaction Logging The database server can keep a record of each change that it makes to the database during a transaction If something happens to cancel the transac tion the database server automatically uses the records to reverse the changes Many things can make a transaction fail The program that issues the SQL statements can crash or be terminated or there might be a hardware or software failure in any other component of the system As soon as the data base server discovers that the transaction failed which might be only after the computer and the database server are restarted it returns the database to the state it was in before the transaction began using the records from the transaction The process of keeping records of transactions is called transaction logging or simply logging The records of the transactions called log records are stored in a
400. ir rowids finding the pair shown in Query Result 3 13 rowid customer_num 515 116 769 116 Query Result 3 13 You can write the last condition in Query 3 13 as shown in the following example AND x rowid y rowid AND NOT x rowid y rowid 3 16 Composing Advanced SELECT Statements Creating Advanced Joins Another way to locate duplicate values is with a correlated subquery as shown in Query 3 14 SELECT x customer_num x call_dtime FROM cust_calls x WHERE 1 lt SELECT COUNT FROM cust_calls y WHERE x customer_num y customer_num Query 3 14 Query 3 14 locates the same two duplicate customer_num values as Query 3 13 and returns the rows shown in Query Result 3 14 customer_num call_dtime 116 1992 11 28 13 34 116 1992 12 21 11 24 Query Result 3 14 You can use the rowid shown earlier in a self join to locate the internal record number associated with a row in a database table The rowid is in effect a hidden column in every table The sequential values of rowid have no special significance and may vary depending on the location of the phys ical data in the chunk Your rowid may vary from the example shown See Chapter 13 Optimizing Your Queries in this manual for a discussion of performance issues and the rowid value The use of rowid is also discussed in detail in the INFORMIX OnLine Dynamic Server Administrator s Guide Composing Advanced SELECT Statements 3 17 Creating
401. is compared to a column in another table a join expression the database server can use the index to find matching values provided that the query plan calls for reading rows from the other table first The following join expression is an example WHERE customer customer_num orders customer_num If rows of customer are read first values of customer_num can be looked up in an index on orders customer_num Whether an index can be used in processing an ORDER BY clause If all the columns in the clause appear in one index in the same sequence the database server can use the index to read the rows in their ordered sequence thus avoiding a sort Whether an index can be used in processing a GROUP BY clause If all the columns in the clause appear in one index in the same sequence the database server can read groups with equal keys from the index without needing a sort 13 10 Optimizing Your Queries The Query Optimizer Selecting Table Access Paths The optimizer next chooses what it estimates to be the most efficient way of accessing each table named in the query It has the following choices e To read the rows of the table sequentially e To read one of the indexes for the table and read the rows to which the index points e To create and use a temporary index e To perform a sort merge The choice between the first two options depends in large part on the presence of a filter expression When any filter exists
402. iteral INTERVAL INTERVAL Field Qualifier segment 1 485S INTO keyword choice of location 5 22T in FETCH statement 5 22T in SELECT 1 318S mismatch signalled in SQLAWARN 5 12T restrictions in INSERT 4 10T restrictions in prepared statement 5 29T retrieving multiple rows 5 20T retrieving single rows 5 13T syntax in FETCH 1 194S in SELECT 1 310S use in FETCH 1 199S in SELECT 1 318S INTO TEMP keywords description of 2 83T restrictions in view 11 22T syntax in SELECT 1 310S use in SELECT 1 3415 with UNION operator 1 3445 IS keyword in Condition segment 1 409S with WHERE keyword 1 327S IS NULL keywords 1 327S ISAM error code 2 315 2 36S 5 12T Isolation level Committed Read 1 367S 7 10T Cursor Stability 1 367S 7 11T default in ANSI compliant database 1 13R definitions 1 367S description of 7 9T Dirty Read 1 3675 7 10T in external tables 1 368S Repeatable Read 1 3675 7 12T setting 7 9T use with FETCH statement 1 201S items table in stores6 database columns in A 3R ITYPE field SET DESCRIPTOR statement 1 357S setting with SET DESCRIPTOR 1 359S with X Open programs 1 213S J Join associative 2 76T creating 2 71T definition of 2 8T dominant table 3 21T effect of large join on optimization 13 36T equi join 2 71T in Condition segment 1 331S multiple table join 1 332S 2 77T natural 2 75T nested outer 3 28T nested simple 3 25T outer 3 21T outer join 1 333S restrictions in modifiable view 11 24T sel
403. ition to the Informix set of manuals the following on line files located in the INFORMIXDIR release directory may supplement the information in this manual Documentation describe features not covered in the manual or that Notes have been modified since publication The file containing the Documentation Notes for this product is called SQLTDOC 6 0 Release Notes describe feature differences from earlier versions of Informix products and how these differences may affect current prod ucts The file containing the Release Notes for Version 6 0 of Informix database server products is called SERVERS_6 0 Machine Notes describe any special actions required to configure and use Informix products on your machine Machine notes are named for the product described for example the machine notes file for INFORMIX OnLine Dynamic Server is ONLINE_6 0 Please read these files because they contain vital information about application and performance issues ASCII and PostScript Error Message Files A number of Informix products also provide on line Help files that walk you through each menu option To invoke the Help feature simply press CTRL W wherever you are in your Informix product ASCII and PostScript Error Message Files Informix software products provide ASCII files that contain all the Informix error messages and their corrective actions To access the error messages in the ASCII file Informix provides scripts that let you display e
404. ivilege on a database can create a stored procedure Once the stored procedure is created it is stored in an executable format in the data base as an object of the database You can use stored procedures to perform any function you can perform in SQL as well as to expand what you can accomplish with SQL alone You write a stored procedure using SQL and SPL statements SPL statements can be used only inside the CREATE PROCEDURE and CREATE PROCEDURE FROM statements The CREATE PROCEDURE statement is available with DB Access and the CREATE PROCEDURE and CREATE PROCEDURE FROM statements are available with SQL APIs such as INFORMIX ESQL C and INFORMIX ESQL COBOL What You Can Do with Stored Procedures You can accomplish a wide range of objectives with stored procedures including improving database performance simplifying the writing of applications and limiting or monitoring access to data Creating and Using Stored Procedures 14 3 Creating and Using Stored Procedures Because a stored procedure is stored in an executable format you can use it to execute frequently repeated tasks to improve performance Executing a stored procedure rather than straight SQL code allows you to bypass repeated parsing validity checking and query optimization Because a stored procedure is an object in the database it is available to every application running on the database Several applications can use the same stored procedure so development time f
405. joined to the name table through the rec_num key The address table also uses a system generated primary key id_num The address table must have a primary key because the business rules state that an address can exist when no names use it If the business rules prevent an address from existing unless a name is associated with it then the address table could be joined to the name table with the foreign key rec_num only Building Your Data Model 8 25 Resolving Your Relationships name rec_num PK inae address bdate id_num PK anniv rec_num FK email street child1 PO Of city child2 state child3 zipcode y Q voice Q fax R modem vce_num PK fax_num PK mdm_num PK rec_num FK rec_num FK rec_num FK vce_type operfrom b300 opertill b1200 b2400 Figure 8 12 Telephone directory diagram with primary and foreign keys added Resolving Your Relationships The aim of a good data model is to create a structure that provides the database server with quick access The telephone directory data model can be further refined by resolving the relationships and normalizing the data model This section addresses the hows and whys of resolving your relationships Normalizing your data model is discussed in Normalizing Your Data Model on page 8 29 Resolving m n Relationships Many to many relationships add complexity and confusion to your model and to the application developmen
406. joins the customer and state tables SELECT UNIQUE city state zipcode sname FROM customer state WHERE customer state state code Query 2 4 Composing Simple SELECT Statements 2 9 Introducing the SELECT Statement Query Result 2 4 is composed of specified rows and columns from both the customer and state tables city state zipcode sname Bartlesville OK 74006 Oklahoma Blue Island NY 60406 New York Brighton MA 02135 Massachusetts Cherry Hill NJ 08002 New Jersey Denver co 80219 Colorado Jacksonville FL 32256 Florida Los Altos CA 94022 California enlo Park CA 94025 California ountain View CA 94040 California ountain View CA 94063 California Oakland CA 94609 California Palo Alto CA 94303 California Palo Alto CA 94304 California Phoenix AZ 85008 Arizona Phoenix AZ 85016 Arizona Princeton NJ 08540 New Jersey Redwood City CA 94026 California Redwood City CA 94062 California Redwood City CA 94063 California San Francisco CA 94117 California Sunnyvale CA 94085 California Sunnyvale CA 94086 California Wilmington DE 19898 Delaware Query Result 2 4 The Forms of SELECT Although the syntax remains the same across all Informix products the form of a SELECT statement and the location and formatting of the resulting output depends on the application The examples in this chapter and in Chapter 3 Composing Advanced SELECT Statements display the SELECT statements and their output as they appear when yo
407. ke the following steps e Examine the application in its context of machines people procedures and organization e Understand exactly what the application does for whom and why Look for nontechnical solutions in the surrounding context Optimizing Your Queries 13 41 Summary e Develop a means of taking repeatable quantitative measurements of the performance of the application Isolate the time consuming parts as narrowly as possible The performance of an individual query is determined by the optimizer a part of the database server that formulates the query execution plan The optimizer exhaustively considers all possible query plans The one with the lowest estimated cost is executed by the database server The following operations in a query are time consuming Reading rows from disk sequentially nonsequentially by ROWID and nonsequentially through an index Reading rows over a network Sorting Performing some difficult matches of regular expressions e Indexing and sorting NCHAR and NVARCHAR columns The general method to speed a query is first to study the query plan of the optimizer as documented by the SET EXPLAIN ON feature and second to change the query so that the database server performs the following actions e Reads fewer pages of data from disk Reads pages sequentially rather than nonsequentially e Avoids sorting or sorts fewer rows or sorts on narrower columns You can achi
408. king at the data for this column you dis cover that more than 50 percent of the addresses list California as the state To save time you specify the string CA as the default value for the State column Check Constraints Check constraints specify a condition or requirement on a data value before data can be assigned to a column during an INSERT or UPDATE statement If a row evaluates to false for any of the check constraints defined on a table dur ing an insert or update the database server returns an error You define a con straint using the CREATE TABLE or ALTER TABLE statements For example the following requirement constrains the values of an integer domain to a certain range Customer_Number gt 50000 AND Customer_Number lt 99999 You can express constraints on character based domains this way using the MATCHES predicate and the regular expression syntax it supports For exam ple the following constraint restricts a Telephone domain to the form of a U S local telephone number vce_num MATCHES 2 9 2 9 0 9 0 9 0 9 0 9 0 9 For additional information about check constraints see the CREATE TABLE and ALTER TABLE statements in the Informix Guide to SQL Syntax Creating the Database Now you are ready to create the data model as tables in a database You do this with the CREATE DATABASE CREATE TABLE and CREATE INDEX state ments The syntax of these statements is shown in detail in the I
409. l the amount of information returned in the SELECT statement with WHERE clauses which are commonly called filters These sections suggest the following ways to improve the WHERE clause of your query e Avoiding correlated subqueries e Avoiding difficult regular expressions Optimizing Your Queries 13 31 Making Queries Faster e Avoiding noninitial substrings Avoiding Correlated Subqueries A correlated subquery is one in which a column label appears in both the select list of the main query and the WHERE clause of the subquery Because the result of the subquery might be different for each row that the database server examines the subquery executes anew for every row if the current cor relation values are different from the previous ones The optimizer tries to use an index on the correlation values to cluster identical values together This procedure can be extremely time consuming Although some queries cannot be stated in SQL without the use of a correlated subquery many can be rewritten as joins that will execute more rapidly When you see a subquery in a time consuming SELECT statement look to see if it is correlated An uncorrelated subquery one in which no row values from the main query are tested within the subquery is executed only once If so try to rewrite the query to avoid it If you cannot look for ways to reduce the number of rows that are examined for instance try adding other filter expressions to the WHERE
410. l_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr customer_num iname company phone call_dtime call_descr Query Result 3 22 Creating Advanced Joins 101 Pauli All Sports Supplies 408 789 8075 102 Sadler Sports Spot 415 822 1289 103 Currie Phil s Sports 415 328 4543 104 Higgins Play Ball 415 368 1100 105 Vector Los Altos Sports 415 776 3249 106 Watson Watson amp Son 415 389 8789 1993 06 12 08 20 Order was received but two of the cans of ANZ tennis balls within the case were empty 107 Ream Athletic Supplies 415 356 9876 108 Quinn Quinn s Sports 415 544 8729 Composing Advanced SELECT Statements 3 25 Creating Advanced Joins Outer Join for a Simple Join to a Third Table Query 3 23 shows an outer join that is the result of a simple join to a third table This second type of outer join is known as a nested simple join SELECT c customer_num c lname o order_num i stock_num i manu_code i quantity FROM customer c OUTER orders o items i WHERE c customer_num o customer_num AND o order_num i order_num AND manu_code IN KAR SHM ORDER BY lname Query 3 23 3 26 Composing Advanced SELECT Statements Query 3 23 first performs a simple join on the orders and items tables Creating Ad
411. lause 1 119S in GROUP BY clause 1 125S in INSERT REFERENCING clause 1 118S in SET clause 1 125S in stored procedure 1 128S in UPDATE REFERENCING clause 1 120S new 1 120S old 1 120S rules for 1 124S scope of 1 125S table of values 1 126S using 1 1245 when to use 1 125S COS function syntax in expression 1 4585 use in expression 1 459S COUNT DISTINCT clause 1 125S COUNT field getting contents with GET DESCRIPTOR 1 210S setting value for WHERE clause 1 354S use in GET DESCRIPTOR 1 212S COUNT function and GROUP BY 3 6T as aggregate function 2 53T count rows to delete 4 5T use in a subquery 4 6T use in expression 1 4635 1 465S with DISTINCT 2 54T COUNT keyword use in SET DESCRIPTOR 1 355S CREATE AUDIT statement need for archive 1 55S starts audit trail 1 55S syntax 1 55S CREATE DATABASE statement and dbspace 10 5T ANSI compliance 1 595 in command script 9 26T logging with OnLine 1 59S sets shared lock 7 6T SQLAWARN after 5 12T syntax 1 57S using with CREATE SCHEMA 1 775 INFORMIX SE 1 608 9 23T OnLine 9 21T PREPARE 1 585 CREATE INDEX statement composite indexes 1 655 implicit table locks 1 635 locks table 7 7T syntax 1 625 usin with CREATE SCHEMA 1 77S using with ASC keyword 1 66S CLUSTER keyword 1 64S DESC keyword 1 665 UNIQUE keyword 1 645 See also Index Name segment CREATE PROCEDURE FROM statement in embedded languages 14 5T syntax and use 1 765 CREATE PROCEDURE statement inside a CREATE PROCE
412. ld about a person Likewise you decide only one kind of address exists no need exists to treat home addresses differently from business ones However you also realize that more than one kind of telephone number exists three Voice numbers are answered by a person fax numbers connect to a fax machine and modem numbers connect to a computer You decide that you want to record different information about each kind of number so these three are different entities For the personal telephone directory example you decide that you want to keep track of the following entities e Name e Address mailing e Telephone number voice Telephone number fax Telephone number modem Building Your Data Model 8 7 Identifying and Defining Your Principal Data Objects Diagramming Your Entities A section in this chapter will teach you how to use the entity relationship diagrams For now create a separate rectangular box for each entity in the telephone directory example You will learn how to put the entities together with relationships in Diagramming Your Data Objects on page 8 16 name address voice fax modem Defining the Relationships After you choose your entities you need to consider the relationships between them Relationships are not always obvious but all of the ones worth recording must be found The only way to ensure that all the relation ships are found is to exhaustively list all possible relatio
413. le INFORMIX OnLine Dynamic Server allocates disk space to a table in multipage extents Extents may be separated on the disk but within an extent the pages are close together Even latency costs may be lowest when pages are read sequentially This depends on the hardware and when operating system files are used on the methods of the operating system Disks are usually set up so that when pages are read sequentially latency is minimized On the other hand it is possible to set up a disk so that a full rotation occurs between each sequential page drastically slowing sequential access Optimizing Your Queries 13 17 Time Costs of a Query The Cost of Nonsequential Access Disk costs are higher when the rows of a table are called for in a sequence that is unrelated to physical order Practical tables are normally much larger than the database server page buffers so only a small part of the table pages can be held in memory When a table is read in nonsequential order only a few rows are found in buffered pages Usually one disk page is read for every row that is requested Because the pages are not taken sequentially from the disk usually both a seek delay and a rotational delay occur before each page can be read In short when a table is read nonsequentially the disk access time is much higher than when it is read sequentially The Cost of Rowid Access The simplest form of nonsequential access is to select a row based on its row
414. led expression Query 2 40 also presents derived values but the column displaying the derived values now has the descriptive header taxed SELECT stock_num description unit unit_descr unit_price unit_price 1 07 taxed FROM stock WHERE unit_price gt 400 Query 2 40 Composing Simple SELECT Statements 2 49 Single Table SELECT Statements Query Result 2 40 shows the label t axed is assigned to the expression in the select list that displays the results of the operation unit_price 1 07 stock_num description unit unit_descr unit_price taxed 1 baseball gloves case 10 gloves case 800 00 856 0000 1 baseball gloves case 10 gloves case 450 00 481 5000 4 football case 24 case 960 00 1027 2000 4 football case 24 case 480 00 513 6000 7 basketball case 24 case 600 00 642 0000 8 volleyball case 24 case 840 00 898 8000 102 bicycle brakes case 4 sets case 480 00 513 6000 111 10 spd assmbld each each 499 99 534 9893 112 12 spd assmbld each each 549 00 587 4300 113 18 spd assmbld each each 685 90 733 9130 203 irons wedge case 2 sets case 670 00 716 9000 Query Result 2 40 In Query 2 41 the label surcharge is defined for the column that displays the results of the operation total_price 6 50 SELECT item_num order_num quantity total_price total_price 6 50 surcharge FROM items WHERE quantity lt 5 Query 2 41 2 50 Composing Simple SELECT Statements Single Table SELECT State
415. leges 11 10T using host file system 11 4T using operating system facilities 11 4T with stored procedures 11 3T Seek time 13 17T Select description of 1 13T Select cursor definition of 1 1485 opening 1 264S 5 20T reopening 1 2675 use of 1 1485 5 20T SELECT keyword ambiguous use as procedure variable 1 480S syntax in GRANT 1 235S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 3025 Select list display label 2 49T expressions in 2 46T functions in 2 53T to 2 66T labels in 3 48T selecting all columns 2 12T selecting specific columns 2 18T specifying a substring in 2 27T Select privilege column level 11 10T definition of 1 236S 11 8T with a view 11 27T SELECT statement active set 2 29T aggregate functions in 1 4625 2 53T alias names 2 79T and COLLCHAR environment variable 4 46R and LC_COLLATE environment variable 4 51R and NLS collation order 1 15R as an argument to a stored procedure 2 4S assigning values with 14 21T associating with cursor with DECLARE 1 148S BETWEEN condition 1 327S column numbers 1 339S compound query 3 43T cursor for 5 19T 5 20T date oriented functions in 2 56T describing returned values with DESCRIBE 1 162S description of advanced 3 4T to 3 55T description of simple 2 3T to 2 83T display label 2 49T DISTINCT keyword 2 19T embedded 5 13T to 5 16T for joined tables 2 69T to 2 83T for single tables 2 11T to 2 66T FROM Clause 1 323S functions 2 53T to 2 66T
416. literal FOREACH SELECT fname lname addressl city state zipcode INTO p_fname p_lname p_add p_city p_state p_zip FROM customer WHERE lname lastname RETURN p_fname p_lname p_add p_city p_state p_zip WITH RESUME LET lcount lcount 1 count of returned addresses END FOREACH TRACE Loop starts Another literal FOR i IN 1 TO 5 BEGIN RETURN i itl i i i i i 1 i with resume END END FOR END PROCEDURE Using the TRACE statement to monitor execution of a procedure Each time you execute the traced procedure entries are added to the file you specified using the SET DEBUG FILE statement To see the debug entries view the output file using any text editor Creating and Using Stored Procedures Privileges on Stored Procedures The following list contains some of the output generated by the procedure in Figure 14 7 Next to each traced statement is an explanation of its contents TRACE ON echoed TRACE ON statement TRACE Foreach starts traced expression in this case the literal string Foreach starts start select cursor notification that a cursor is opened to handle a FOREACH loop select cursor iteration notification of the start of each iteration of the select cursor expression lcount 1 the encountered expression lcount 1 evaluates to 2 let lcount 2 each LET statement is echoed with the value Re creating a Procedure If a procedure exists in a database you must d
417. litting Tall Tables A large table poses large management problems The 400 megabyte table takes a long time to query of course and it also takes a long time to back up or restore Sorting becomes radically slower because the sort goes to three or more merge levels sorting can even become impossible because too much disk space is required Indexes become less effective because the index structure has three or more intermediate levels Consider splitting such a table into segments Each segment has the same arrangement of columns indexes and constraints but a different subset of rows The division into groups of rows should be based on the value of an attribute that appears in most queries probably the primary key so that a program or user can easily tell in which subtable a row belongs For example if the primary key is a number rows can be allocated to 10 subtables based on a middle digit If rows include a time or date attribute it might be useful to split a table into segments by age especially if recent rows are used more often than older ones Tuning Your Data Model 10 29 Denormalizing The benefits of splitting a large table are that the segments can be treated separately for copying sorting indexing archiving and restoring All these operations become easier The segments can be assigned to tblspaces in dif ferent ways to make the best use of disk devices And as long as most queries are based on the attribute used f
418. lled GET DIAG NOSTICS in Chapter 1 of the Informix Guide to SQL Syntax If your Informix product supports GET DIAGNOSTICS and SQLSTATE Informix recommends that you use them as the primary structure to detect handle and diagnose errors Retrieving Single Rows You can use embedded SELECT statements to retrieve single rows from the database into host variables When a SELECT statement returns more than one row of data however a program must use a more complicated method to fetch the rows one at a time Multiple row select operations are discussed in Retrieving Multiple Rows on page 5 19 To retrieve a single row of data simply embed a SELECT statement in your program The following example shows how it can be written using INFORMIX ESQL C exec sql select avg total_price into avg_price from items where order_num in select order_num from orders where order_date lt date 6 1 93 The INTO clause is the only detail that distinguishes this statement from any example in Chapter 2 Composing Simple SELECT Statements or Chapter 3 Composing Advanced SELECT Statements This clause specifies the host variables that are to receive the data that is produced Programming with SQL 5 13 Retrieving Single Rows When the program executes an embedded SELECT statement the database server performs the query The example statement selects an aggregate value so that it produces exactly one row of data The
419. ller_number UPDATE branch SET balance balance WHERE branch_number INSERT INTO history VALUES timestamp values G v TO BIG QUERY EXEC SQL PREPARE BIG Q FROM BIG QUERY END EXEC Figure 5 7 Preparing a string containing five SQL statements When this list of statements is executed host variables must provide values for six place holding question marks Although it is more complicated to set up a multistatement list the performance is often better because fewer exchanges take place between the program and the database server 5 30 Programming with SQL Dynamic SQL Executing Prepared SOL Figure 5 8 Once a statement is prepared it can be executed multiple times Statements other than SELECT statements and SELECT statements that return only a single row are executed with the EXECUTE statement Figure 5 8 shows how INFORMIX ESQL C prepares and executes a multistatement update of a bank account exec sql begin declare section char bigquery 270 begin work exec sql end declare section stcat update account set balance balance where bigquery stcat acct_number bigquery stcat update teller set balance balance where bigquery stcat teller_number bigquery stcat update branch set balance balance where bigquery stcat branch_number bigquery stcat insert into history values timestam
420. lock 7 15 Simple Concurrency 7 15 Locking with Other Database Servers 7 16 Isolation While Reading 7 17 Locking Updated Rows 7 17 Hold Cursors 7 18 Summary 7 19 Chapter 8 Building Your Data Model Chapter Overview 8 3 Why Build a Data Model 8 3 Entity Relationship Data Model Overview 8 3 Identifying and Defining Your Principal Data Objects 8 4 Discovering Entities 8 4 Defining the Relationships 8 8 Identifying Attributes 8 14 Diagramming Your Data Objects 8 16 Translating E R Data Objects Into Relational Constructs 8 20 Rules for Defining Tables Rows and Columns 8 20 Determining Keys for Tables 8 22 Resolving Your Relationships 8 26 Normalizing Your Data Model 8 29 Summary 8 33 Chapter 9 Implementing Your Data Model Chapter Overview 9 3 Defining the Domains 9 3 Data Types 9 4 Default Values 9 19 Check Constraints 9 20 Table of Contents xi Chapter 10 xii Table of Contents Creating the Database 9 20 Using CREATE DATABASE 9 21 Using CREATE TABLE 9 24 Using Command Scripts 9 26 Populating the Tables 9 27 Summary 9 29 Tuning Your Data Model Chapter Overview 10 3 INFORMIX OnLine Dynamic Server Disk Storage 10 3 Chunks and Pages 10 4 Dbspaces and Blobspaces 10 4 Disk Mirroring 10 5 Databases 10 5 Tables and Spaces 10 6 Tblspaces 10 7 Extents 10 8 Reorganizing dbspaces and Tables 10 10 Calculating Table Sizes 10 12 Estimating Fixed Length Rows 10 13 Estimating Variable Length Rows 10 14 Esti
421. lock on an index key value Key locks are used identically to row locks When the table uses row locking key locks are implemented as locks on imaginary rows When it uses page locking a key lock is placed on the index page that contains the key or that would contain the key if the it existed The Duration of a Lock The program controls the duration of a database lock A database lock is released when the database closes The duration of a table lock depends on whether the database uses transactions If it does not that is if no transaction log exists and the COMMIT WORK statement is not used a table lock remains until it is removed by the execution of the UNLOCK TABLE statement The duration of table row and index locks depends on what SQL statements are used and on whether transactions are in use When transactions are used the end of a transaction releases all table row page and index locks This is an important point When a transaction ends all locks are released 7 8 Programming for a Multiuser Environment Setting the Isolation Level Locks While Modifying When the database server fetches a row through an update cursor it places a promotable lock on the fetched row If this succeeds the database server knows that no other program can alter that row Because a promotable lock is not exclusive other programs can continue to read the row This helps per formance because the program that fetched the row can take s
422. locked row it immediately receives an error code for example error 107 Record is locked and the current SQL statement terminates It is up to the program to roll back its current transaction and try again The initial setting is not waiting when a program starts up If you are using SQL interactively and see an error related to locking set the lock mode to wait If you are writing a program consider making that one of the first embedded SQL commands that the program executes Waiting a Limited Time When you use INFORMIX OnLine Dynamic Server you have an additional choice You can ask the database server to set an upper limit on a wait You can issue the following command SET LOCK MODE TO WAIT 17 This places an upper limit of 17 seconds on the length of any wait If a lock is not removed in that time the error code is returned Handling a Deadlock A deadlock is a situation in which a pair of programs block the progress of each other Each program has a lock on some object that the other program wants to access A deadlock arises only when all programs concerned set their lock modes to wait for locks INFORMIX OnLine Dynamic Server detects deadlocks immediately when they involve only data at a single network server It prevents the deadlock from occurring by returning an error code error 143 ISAM error dead lock detected to the second program to request a lock The error code is 7 14 Programming for a Multiuser Envir
423. ly the rows found in Query Result 2 33 stock_num manu_code description unit_price unit unit_descr 102 SHM bicycle brakes 220 00 case 4 sets case 101 SHM bicycle tires 68 00 box 4 box 105 SHM bicycle wheels 80 00 pair pair Query Result 2 33 When you select from a large table and use an initial wildcard in the comparison string such as cycle the query often takes longer to execute This is because indexes cannot be used so every row is searched MATCHES and Native Language Support As indicated on page 2 25 you can set the DBNLS LANG and LC_COLLATE environment variables to influence NLS functionality regarding the collation order of data returned by a query Query 2 34 uses an ORDER BY clause and a WHERE clause specifying a match ing range on a column containing data of type NCHAR This NLS table abon n s is provided separately from the demonstration database Query 2 34 is provided as the sel_nls2 sql command file with NLS enabled DB Access SELECT num ro nom pr nom FROM abonn s WHERE nom MATCHES E P ORDER BY nom Query 2 34 The output in Query Result 2 34a and Query Result 2 34b show different rows selected for the MATCHES range by the same query based on different NLS environment variable settings num ro nom pr nom 13607 Hammer Gerhard 13602 H mmerle Greta 13604 LaFor t Jean No l 13610 LeMaitre H loise 13613 Llanero Gloria Dolores 13603 Monta a Jos Antonio 13611 Oatfield E
424. m administrator The DBPATH environment variable is optional If the application does not fully specify the location of an SE database server the directories listed in DBPATH are searched by the database server to find the specified database 12 14 Understanding Informix Networking Connecting to Data on a UNIX Network The DBPATH environment variable is also used to specify directory names for reports forms and command files used by both INFORMIX OnLine Dynamic Server and INFORMIX SE These environment variables are described in detail in Chapter 4 of the Informix Guide to SQL Reference Connection Information When the INFORMIX OnLine Dynamic Server or INFORMIX SE administrator installs and configures a database server he or she must cooperate with the UNIX system administrator to specify the information that allows a client application to locate a database server The application specifies a database server and the Informix connectivity tools make the connection The connection is transparent the client does not need to know where the database server resides The connection information is specified in the INFORMIXDIR etc sqlhosts file and two UNIX systems files etc hosts and etc services The three files working together specify the location of the database server and the type of connection protocol for the database server See Figure 12 7 On each com puter every database server that might be accessed by an applicat
425. m and your computer hardware Multiuser operating systems have software facilities such as UNIX file permissions Note In UNIX the database directory is created with group identity informix and the database server always runs under group identity informix Thus you cannot use group permissions to restrict access to a particular group of users You can how ever only remove all group permissions file mode 700 and deny access to anyone except the owner of the directory You also can deny access to individual tables in this way for example by making the files that represent those tables unavailable to certain users while leaving the rest of the files accessible However the database servers are not designed for tricks of this kind When an unauthorized user tries to query one of the tables the database server probably returns an error message about not being able to locate a file This may confuse users Single User Systems Typical single user systems have few software controls on file access you can make a database inaccessible to others only by writing it on a disk that you can detach from the machine and keep locked None of these techniques apply when you use the INFORMIX OnLine Dynamic Server database server It controls its own disk space at the device level bypassing the file access mechanisms of the operating system 11 4 Granting and Limiting Access to Your Database Granting Privileges Securing Confidential Data
426. mating Index Pages 10 16 Estimating Blobpages 10 17 Locating Blob Data 10 18 Managing Indexes 10 19 Space Costs of Indexes 10 20 Time Costs of Indexes 10 20 Choosing Indexes 10 21 Duplicate Keys Slow Index Modifications 10 22 Dropping Indexes 10 24 Clustered Indexes 10 25 Denormalizing 10 26 Shorter Rows for Faster Queries 10 26 Expelling Long Strings 10 26 Splitting Wide Tables 10 28 Splitting Tall Tables 10 29 Redundant and Derived Data 10 30 Maximizing Concurrency 10 32 Easing Contention 10 32 Rescheduling Modifications 10 33 Isolating and Dispersing Updates 10 35 Summary 10 36 Chapter 11 Chapter 12 Granting and Limiting Access to Your Database Chapter Overview 11 3 Controlling Access to Databases 11 4 Securing Database Files 11 4 Securing Confidential Data 11 5 Granting Privileges 11 5 Database Level Privileges 11 5 Ownership Rights 11 7 Table Level Privileges 11 7 Procedure Level Privileges 11 12 Automating Privileges 11 13 Controlling Access to Data Using Stored Procedures 11 15 Restricting Reads of Data 11 16 Restricting Changes to Data 11 16 Monitoring Changes to Data 11 17 Restricting Object Creation 11 18 Using Views 11 19 Creating Views 11 20 Modifying Through a View 11 23 Privileges and Views 11 27 Privileges When Creating a View 11 27 Privileges When Using a View 11 28 Summary 11 30 Understanding Informix Networking Chapter Overview 12 3 What Is a Network 12 4 Database Management Sys
427. ment Index 9 column data types 1 137S privileges 1 137S restrictions on 11 22T syntax 1 136S use of dbschema 5 34R using 11 20T virtual column 1 137S WITH CHECK OPTION 1 138S with CREATE SCHEMA 1 77S with SELECT notation 1 136S Creating a database from ASCII files 5 14R a dbload command file 5 23R crtcmap utility creating mapping files 5 5R description of 5 5R error messages for 5 7R formats for mapping files 5 6R Currency representing with NLS 1 15R Current database specifying with DATABASE 1 140S CURRENT function 4GL example 13 6T comparing column values 2 56T syntax in Condition segment 1 405S in expression 1 436S in INSERT 1 250S use in ALTER TABLE 1 18S in CREATE TABLE 1 888 in expression 1 440S in INSERT 1 252S in WHERE condition 1 441S input for DAY function 1 441S CURRENT keyword DISCONNECT statement 1 168S syntax in FETCH 1 1945 use in FETCH 1 196S CURRENT OF keywords syntax in DELETE 1 159S in UPDATE 1 383S use in DELETE 1 161S in UPDATE 1 390S Cursor activating with OPEN 1 263S active set of 5 24T affected by transaction end 1 40S 10 Index associating with prepared statements 1 154S characteristics 1 149S closing 1 388 7 18T closing with ROLLBACK WORK 1 307S declaring 1 145S 5 20T definition of types 1 148S for insert 6 8T for update 6 15T 7 9T hold 7 18T manipulation statements 1 6S opening 1 264S 1 265S 5 20T 5 24T retrieving values with FETCH 1 194S 5 21T scroll 1 149S 5 23
428. ment adds a new row or rows to a table The statement has two basic functions It can create a single new row using column values you supply or it can create a group of new rows using data selected from other tables Statements That Modify Data Single Rows In its simplest form the INSERT statement creates one new row from a list of column values and puts that row in the table The following statement is an example of adding a row to the stock table INSERT INTO stock VALUES 115 PRC tire pump 108 box 6 box The stock table has the following columns stock_num a number identifying the type of merchandise manu_code a foreign key to the manufact table description a description of the merchandise unit_price the unit price of the merchandise unit of measure unit_descr characterizing the unit of measure Notice that the values listed in the VALUES clause in the preceding example have a one to one correspondence with the columns of this table To write a VALUES clause you must know the columns of the tables as well as their sequence from first to last Possible Column Values The VALUES clause accepts only constant values not expressions You can supply the following values Literal numbers e Literal datetime values Literal interval values Quoted strings of characters The word NULL for a null value The word TODAY for today s date The word CURRENT for the current d
429. ment as it might appear when embedded in a COBOL source program EXEC SQL DELETE FROM items WHERE order_num o num END EXEC The first and last lines mark off embedded SQL from the normal COBOL statements Between them you see an ordinary DELETE statement as described in Chapter 4 Modifying Data When this part of the COBOL program is executed a row of the items table is deleted multiple rows can also be deleted The statement contains one new feature It compares the order_num column to an item written as o num which is the name of a host variable Each SQL API product provides a means of delimiting the names of host variables when they appear in the context of an SQL statement In COBOL host variable names are designated with an initial colon The example state ment asks the database server to delete rows in which the order number equals the current contents of the host variable named o num This is a numeric variable that has been declared and assigned a value earlier in the program 5 6 Programming with SQL SQL in Programs The same statement embedded in a FORTRAN program looks like the following example EXEC SQL DELETE FROM items WHERE order_num onum The same statement embedded in an Ada program looks like the following example EXEC SQL DELETE FROM items WHERE order_num Sonum In INFORMIX ESQL Ada a host variable is indicated by a leading dollar sign and stat
430. ment clauses in your queries The clauses must appear in the following order 1 SELECT 2 FROM 3 WHERE 4 GROUP BY 5 HAVING 6 ORDER BY 7 INTO TEMP An additional SELECT statement clause INTO which you can use to specify program and host variables in INFORMIX 4GL and SQL APIs is described in Chapter 5 Programming with SQL as well as in the manuals that come with the product Using the GROUP BY and HAVING Clauses The optional GROUP BY and HAVING clauses add functionality to your SELECT statement You can include one or both in a basic SELECT statement to increase your ability to manipulate aggregates The GROUP BY clause combines similar rows producing a single result row for each group of rows that have the same values for each column listed in the select list The HAVING clause sets conditions on those groups after you form them You can use a GROUP BY clause without a HAVING clause or a HAVING clause without a GROUP BY clause Using the GROUP BY Clause The GROUP BY clause divides a table into sets It is most often combined with aggregate functions that produce summary values for each of those sets Some of the examples in Chapter 2 Composing Simple SELECT State ments show the use of aggregate functions applied to a whole table This chapter illustrates aggregate functions applied to groups of rows 3 4 Composing Advanced SELECT Statements Using the GROUP BY and HAVING Clauses Using the GROUP B
431. ments The surcharge column is labeled in the output as shown in Query Result 2 41 item_num order_num quantity total_price surcharge 2 1013 1 36 00 42 50 3 1013 1 48 00 54 50 4 1013 2 40 00 46 50 1 1014 1 960 00 966 50 2 1014 al 480 00 486 50 1 1015 al 450 00 456 50 1016 2 136 00 142 50 2 1016 3 90 00 96 50 3 1016 1 308 00 314 50 4 1016 1 120 00 126 50 1 1017 4 150 00 156 50 2 1017 1 230 00 236 50 Query Result 2 41 Query 2 42 assigns the label span to the column that displays the results of subtracting the DATETIME column call_dtime from the DATETIME column res_dtime SELECT customer_num user_id call_code call_dtime res_dtime call_dtime span FROM cust_calls ORDER BY user_id Query 2 42 The span column is labeled in the output as shown in Query Result 2 42 customer_num user_id call_code call_dtime span 116 mannyn T 1992 12 21 11 24 20 55 116 mannyn I 1992 11 28 13 34 0 03 13 106 maryj D 1993 06 12 08 20 0 00 05 121 maryj 0 1993 07 10 14 05 0 00 01 127 maryj I 1993 07 31 14 30 110 riche L 1993 07 07 10 24 0 00 06 119 riche B 1993 07 01 15 00 0 17 21 Query Result 2 42 Composing Simple SELECT Statements 2 51 Single Table SELECT Statements Sorting on Derived Columns When you want to use ORDER BY as an expression you can use either the display label assigned to the expression or an integer as shown in Query 2 43 SELECT customer_num user_id call_c
432. ments on line address your e mail to doc informix com Preface v Related Reading vi Preface If you want additional technical information on database management consult the following texts by C J Date e An Introduction to Database Systems Volume I Addison Wesley Publishing 1990 e An Introduction to Database Systems Volume II Addison Wesley Publishing 1983 This guide assumes that you are familiar with your computer operating sys tem If you have limited UNIX system experience you might want to look at your operating system manual or a good introductory text before you read this tutorial The following list contains some suggested texts about UNIX systems e A Practical Guide to the UNIX System Second Edition by M Sobell Benjamin Cummings Publishing 1989 e A Practical Guide to UNIX System V by M Sobell Benjamin Cummings Publishing 1985 Introducing the UNIX System by H McGilton and R Morgan McGraw Hill Book Company 1983 UNIX for People by P Birns P Brown and J Muster Prentice Hall 1985 If you are interested in learning more about SQL consider the following text e Using SQL by J Groff and P Weinberg Osborne McGraw Hill 1990 Chapter 1 Table of Contents Introduction Informix Products That Use SQL 3 Products Included in This Manual 3 Other Useful Documentation 4 How to Use This Manual 5 Typographical Conventions 5 Example Code Conventions 5 Useful On Line File
433. mer_num call_code call_descr FROM cust_calls WHERE call_dtime lt CURRENT YEAR TO DAY Query 2 55 customer_num call_code D call_descr balls wit customer_num call_code I call_descr R customer_num ca ca navy with _code T _descr Ss two cases one case Query Result 2 55 2 58 Composing Simple SELECT Statements 06 Order was received but two of the cans of ANZ tennis hin the case were empty 16 eceived plain white swim caps 313 ANZ instead of team logo 313 SHM 16 econd complaint from this customer Received right handed outfielder gloves 1 HRO instead of efties Single Table SELECT Statements Using MONTH Query 2 56 uses the MONTH function to extract and show what month the customer call was received and resolved and uses display labels for the resulting columns However it does not make a distinction between years SELECT customer_num MONTH call_dtime call_month MONTH res_dtime res_month FROM cust_calls Query 2 56 customer_num call_month res_month 106 6 6 110 7 7 119 7 7 121 7 7 127 7 116 11 11 116 12 1 2 Query Result 2 56 Query 2 57 uses the MONTH function plus DAY and CURRENT to show what month the customer call was received and resolved if DAY is earlier than the current day SELECT customer_num MONTH call_dtime called MONTH res_dtime resolved FROM cust_calls WHERE DAY res_dtime lt DAY CURRENT Query 2 57 customer_
434. mily Query Result 2 34a 2 42 Composing Simple SELECT Statements Single Table SELECT Statements In Query Result 2 34a the rows for Etaix Otker and verst are not selected and listed because with standard ASCII ordering the accented first letter of each name is not in the E P MATCHES range for the nom column num ro nom pr nom 13608 Etaix Emile 13607 Hammer Gerhard 13602 Hammerle Greta 13604 LaFor t Jean No l 13610 LeMaitre H loise 13613 Llanero Gloria Dolores 13603 Montafia Jos Antonio 13611 Oatfield Emily 13605 Otker Hans J rgen 13614 verst Per Anders Query Result 2 34b In Query Result 2 34b the rows for taix tker and verst are included in the list because with the appropriate NLS environment variable settings the accented first letter of each name is in the E P MATCHES range for the nom column Comparing for Special Characters Query 2 35 uses the keyword ESCAPE with LIKE or MATCHES so you can protect a special character from misinterpretation as a wildcard symbol SELECT FROM cust_calls WHERE res_descr LIKE oe oe oe ESCAPE M1 Query 2 35 The ESCAPE keyword designates an escape character it is an exclamation point in this example which protects the next character so it is interpreted as data and not as a wildcard In the example the escape character causes the middle percent sign to be treated as data By using the ESCAPE keyword you
435. mirrored the root dbspace should also be mirrored Otherwise if it is lost to hardware failure all OnLine data is unusable regardless of mirrors If your database has extreme requirements for reliability in the face of hardware failure you should place it in a mirrored dbspace As indicated in Tables and Spaces on page 10 6 it is possible to locate individual tables in particular dbspaces Hence you can place some tables in mirrored spaces and other tables in normal spaces Databases A database resides initially in one dbspace It is placed there by a parameter of the CREATE DATABASE statement The following example creates a database in the dbspace named dev0x2d CREATE DATABASE reliable IN dev0x2d WITH BUFFERED LOG When no dbspace is specified a database is placed in the root dbspace When a database is in a dbspace it means only that the following conditions have been met e Its system catalog tables are stored in that dbspace e That dbspace is the default location for tables that are not explicitly created in other dbspaces Tuning Your Data Model 10 5 INFORMIX OnLine Dynamic Server Disk Storage Tables and Spaces A table resides completely in one dbspace Its blob values can reside in separate blobspaces or on an optical storage subsystem If no dbspace is specified a table resides in the dbspace where its database resides The following partial example creates a table in the dbspace named misctabs
436. mited range of values they can store The database server does not store a value that exceeds the capacity of an integer Of course this is not a problem when you know the maximum and minimum values to be stored Automatic Sequences SERIAL The SERIAL data type is simply INTEGER with a special feature Whenever a new row is inserted into a table the database server automatically generates a new value for a SERIAL column A table can have only one SERIAL column Because the database server generates them the serial values in new rows are always different even when multiple users are adding rows at the same time This is a useful service because it is quite difficult for an ordinary program to coin unique numeric codes under those conditions Implementing Your Data Model 9 7 Defining the Domains How Many Serialized Rows After inserting 2 rows in a table the database server uses up all the positive serial numbers Should you be concerned about this Probably not because to make this happen you need to insert a row every second for 68 years However if it did occur the database server would continue generat ing new numbers It would treat the next serial quantity as a signed integer Because it uses only positive values it would simply wrap around and start generating integer values beginning with 1 The sequence of generated numbers always increases When rows are deleted from the table their serial numbers are not reused T
437. mix tools expect that a TEXT item is printable so this data type should be restricted to printable ASCII text Implementing Your Data Model 9 17 Defining the Domains How Blobs Are Used Collectively columns of type TEXT and BYTE are called binary large objects or blobs The database server simply stores and retrieves them Normally blob values are fetched and stored by programs written using INFORMIX 4GL or a language that supports embedded SQL such as INFORMIX ESQLIC In such a program you can fetch insert or update a blob value in a manner similar to the way you read or write a sequential file In any SQL statement interactive or programmed a blob column cannot be used in the following ways Inarithmetic or Boolean expressions Ina GROUP BY or ORDER BY clause e Ina UNIQUE test e For indexing either by itself or as part of a composite index In a SELECT statement entered interactively or in a form or report a blob can only perform the following functions Be selected by name optionally with a subscript to extract part of it e Have its length returned by selecting LENGTH column Be tested with the IS NOT NULL predicate In an interactive INSERT statement you can use the VALUES clause to insert a blob value but the only value you can give that column is null However you can use the SELECT form of the INSERT statement to copy a blob value from another table In an interactive UPDATE statement you c
438. most important part of the rela tional database design process Once you have determined the entities and relationships you might find it helpful to have a method for displaying your thought process during database design 8 16 Building Your Data Model Figure 8 7 Diagramming Your Data Objects Most data modeling methods provide some form of graphically displaying your entities and relationships Informix uses the entity relationship diagram approach originally developed by C R Bachman Entity relationship diagrams serve the following purposes They model the information needs of an organization e They identify entities and their relationships e They provide a starting point for data definition data flow diagrams e They provide an excellent source of documentation for application developers as well as database and system administrators e They create a logical design of the database which can be translated into a physical schema Several different styles of documenting entity relationship diagrams exist If you already have a style that you prefer use it A sample entity relationship diagram is represented by the following symbols name address A A entity e C entity relationship Symbols of an entity relationship diagram Entities are represented by a box Relationships are represented by a line connecting the entities In addition you use several graphical items to dis pla
439. mprove Expelling Long Strings The most bulky attributes are often character strings If you can remove them from the entity table the rows become shorter Using VARCHAR Strings An existing database might contain CHAR columns that can be converted profitably to VARCHAR VARCHAR columns shorten the average row when the average value in the CHAR column is at least 2 bytes shorter than the 10 26 Tuning Your Data Model Denormalizing existing fixed width of the column When NLS is enabled NCHAR columns may replace CHAR columns and NVARCHAR columns may replace VARCHAR columns This CHAR VARCHAR or NCHAR NVARCHAR substitution does not harm the theoretical characteristics of the model Furthermore VARCHAR data is immediately compatible with most existing programs forms and reports Forms must be recompiled Forms and reports should of course be tested on a sample database Changing Long Strings to TEXT When the typical string fills half a disk page or more consider converting it to a TEXT column in a separate blobspace The column within the row page is only 56 bytes long which should put many more rows ona page However the TEXT data type is not automatically compatible with existing programs The code for fetching a TEXT value is more complicated than the code for fetching a CHARACTER value into a program Building a Symbol Table of Repeated Strings If a column contains strings that are not unique in each row yo
440. ms WHERE total_price lt ALL SELECT total_price FROM items WHERE order_num 1023 Query 3 27 order_num stock_num manu_code total_price 1003 9 ANZ 20 00 1005 6 SMT 36 00 1006 6 SMT 36 00 1010 6 SMT 36 00 1013 5 ANZ 19 80 1013 6 SMT 36 00 1018 302 KAR 15 00 Query Result 3 27 Using ANY Use the keyword ANY or its synonym SOME preceding a subquery to determine whether a comparison is true for at least one of the values returned If the subquery returns no values the search condition is false Because there were no values the condition cannot be true for one of them 3 34 Composing Advanced SELECT Statements Subqueries in SELECT Statements Query 3 28 finds the order number of all orders that contain an item for which the total price is greater than the total price of any one of the items in order number 1005 SELECT DISTINCT order_num FROM items WHERE total_price gt ANY SELECT total_price FROM items WHERE order_num 1005 Query 3 28 order_num 1001 1002 1003 1004 1005 1006 1007 1008 1009 101 101 101 101 101 101 101 101 101 1019 1020 1021 1022 1023 gt ANA HBWNE Query Result 3 28 Composing Advanced SELECT Statements 3 35 Subqueries in SELECT Statements Single Valued Subqueries You do not need to include the keyword ALL or ANY if you know the subquery can return exactly one value to the outer level query A subquery that returns exac
441. ms table items table qualifies exists in stock table stock_num items table not in stock table Figure 3 2 The intersection set operation Query 3 42 is an example of a nested SELECT statement that shows the intersection of the stock and items tables SELECT stock_num manu_code unit_price FROM stock WHERE stock_num IN SELECT stock_num FROM items ORDER BY stock_num Query 3 42 Query Result 3 42 contains all the elements from both sets returning the following 57 rows Composing Advanced SELECT Statements 3 51 Set Operations stock_num DBINDAMVUUHBBRWWNHRER oO 01 01 03 04 05 05 09 09 10 10 10 10 10 11 14 201 201 201 202 202 204 205 205 205 301 301 301 301 301 301 302 302 303 303 304 304 306 306 307 309 309 Query Result 3 42 3 52 Composing Advanced SELECT Statements manu_code unit_price HRO HSK SMT HRO HSK SHM HRO HSK ANZ NRG SMT ANZ SMT HRO ANZ ANZ PRC SHM PRC PRC PRC SHM PRC SHM ANZ HRO HSK PRC SHM SHM PRC ANZ KAR NKL KAR NKL KAR ANZ HRO NKL ANZ HRO KAR NKL PRC SHM HRO KAR KAR PRC ANZ HRO PRC SHM PRC HRO SHM 250 800 450 126 240 280 480 960 19 28 25 48 36 600 840 20 88 68 20 58 53 80 30 200 244 260 308 236 228 499 120 75 90 37 230 174 45 312 312 312
442. n Query Result 2 8 manu_code manu_name lead_time SHM Shimara 30 KAR Karsten 21 PRC ProCycle 9 NKL Nikolus 8 NRG Norge 7 HSK Husky 5 ANZ Anza 5 HRO Hero 4 SMT Smith 3 Query Result 2 8 You can specify any column except TEXT or BYTE in the ORDER BY clause and the database server sorts the data based on the values in that column Sorting on Multiple Columns You can also ORDER BY two or more columns creating a nested sort The default is still ascending and the column listed first in the ORDER BY clause takes precedence The following two queries and corresponding query results show nested sorts The order in which selected data is displayed is modified by changing the order of the two columns named in the ORDER BY clause SELECT FROM stock ORDER BY manu_code unit_price Query 2 9 Composing Simple SELECT Statements 2 15 Single Table SELECT Statements In Query Result 2 9 the manu_code column data appears in alphabetical order and within each set of rows with the same manu_code for example ANZ HRO the unit_price is listed in ascending order stock_num manu_code description unit_price unit unit_descr 5 ANZ tennis racquet 19 80 each each 9 ANZ volleyball net 20 00 each each 6 ANZ tennis ball 48 00 case 24 cans case 313 ANZ swim cap 60 00 box 12 box 201 ANZ golf shoes 75 00 each each 310 ANZ kick board 84 00 case 12 case 301 ANZ running shoes 95 00 each each 304 ANZ watch 170 00 box 10
443. n any manufacturer of that product You need to update the prices of all unshipped orders The SELECT statements in the following example specify the criteria UPDATE items SET total_price quantity SELECT MAX unit_price FROM stock WHERE stock stock_num items stock_num WHERE items order_num IN SELECT order_num FROM orders WHERE ship_date IS NULL The first SELECT statement returns a single value the highest price in the stock table for a particular product This is a correlated subquery because when a value from items appears in its WHERE clause you must execute it for every row that you update The second SELECT statement produces a list of the order numbers of unshipped orders It is an uncorrelated subquery that is executed once Impossible Updates Restrictions exist on the use of subqueries when you modify data In particular you cannot query the table that is being modified You can refer to the present value of a column in an expression as in the example in which the unit_price column was incremented by 5 percent You can refer to a value of Modifying Data 4 13 Statements That Modify Data a column in a WHERE clause in a subquery as in the example that updated the stock table in which the items table is updated and items stock_num is used in a join expression The need to update and query a table at the same time does not occur often in a well designed database Database design is co
444. n contain multiple conditions connected by AND and OR and it may contain subqueries Suppose you discover that some rows of the stock table contain incorrect manufacturer codes Rather than update them you want to delete them so they can be reentered You know that these rows unlike the correct ones have no matching rows in the manufact table This allows you to write a DELETE statement such as the one shown in the following example DELETE FROM stock WHERE 0 SELECT COUNT FROM manufact WHERE manufact manu_code stock manu_code The subquery counts the number of rows of manufact that match the count is 1 for a correct row of stock and 0 for an incorrect one The latter rows are chosen for deletion One way to develop a DELETE statement with a complicated condition is to first develop a SELECT statement that returns precisely the rows to be deleted Write itas SELECT when it returns the desired set of rows change SELECT x to read DELETE and execute it once more The WHERE clause of a DELETE statement cannot use a subquery that tests the same table That is when you delete from stock you cannot use a subquery in the WHERE clause that also selects from stock The key to this rule is in the FROM clause If a table is named in the FROM clause of a DELETE statement it cannot also appear in the FROM clause of a subquery of the DELETE statement Inserting Rows 4 6 Modifying Data The INSERT state
445. n drastically reduce the speed of updating An example is a column whose values are the names or abbrevia tions of states or provinces If 50 unique values occur in a mailing list of 100 000 rows an average of 2 000 duplicates exists per value But real data is never so well distributed in such a table the more common values likely have 10 000 or more duplicates and their lists might approach 50 pages in length When the database server inserts or deletes an entry in such a list it is busy for a long time Worse still it has to lock all the affected index pages while it does the work greatly reducing concurrent access to the table You can avoid this problem fairly simply at some cost in disk space The trick is to know that the database server uses the leading column of a composite index in the same way as it uses an index on that column alone So instead of creating an index on a column with few unique values create a composite index on that column followed by one other column that has a wide distribution of values For example change the index on the column whose only values are M and S into a composite index on that column and a birthdate column You can use any second column to disperse the key values as long as its value does not change or changes at the same time as the real key The shorter the second column the better because its values are copied into the index and expand its size Tuning Your Data Model 10 23 Managing Inde
446. n names in temporary table 3 12T use in ORDER BY clause 1 338S use with GROUP BY clause 1 334S with self join 3 11T See also Synonym ALL keyword beginning a subquery 1 330S 3 33T DISCONNECT statement 1 169S syntax in expression 1 462S in GRANT 1 235S in REVOKE 1 301S in SELECT 1 312S with UNION operator 1 310S use in Condition subquery 1 415S in expression 1 463S in GRANT 1 236S in SELECT 1 313S with UNION operator 1 344S ALLOCATE DESCRIPTOR statement syntax 1 95 with concatenation operator 1 432S Allocating memory with the ALLOCATE DESCRIPTOR statement 1 95 ALTER INDEX statement creating clustered index 1 125 10 25T dropping clustered index 1 135 locks table 7 7T syntax 1 128 See also Index Name segment ALTER keyword syntax in GRANT 1 231S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 302S Alter privilege 1 2365S 11 8T ALTER TABLE statement ADD clause 1 17S ADD CONSTRAINT clause 1 30S adding a column 1 175 adding a column constraint 1 295 and NCHAR column 1 19R and NVARCHAR column 1 19R cascading deletes 1 225 changing column data type 1 275 9 19T changing table lock mode 1 33S CHECK clause 1 25S DEFAULT clause 1 188 DROP clause 1 26S DROP CONSTRAINT clause 1 32S dropping a column 1 265 dropping a column constraint 1 32S LOCK MODE clause 1 33S MODIFY NEXT SIZE clause 2 9R 1 33S NEXT SIZE clause 10 8T ON DELETE CASCADE keyword 1 21S PAGE keyword 1 335 privilege for 1 231S 11 10T reclustering a
447. n selecting attributes choose ones that have the following qualities They are significant Include only attributes that are useful to the users of the database They are direct not derived An attribute that can be derived from existing attributes for instance through an expression in a SELECT statement should not be made part of the model The presence of derived data greatly complicates the maintenance of a database Ata later stage of the design discussed in Chapter 10 Tuning Your Data Model you can consider adding derived attributes to improve performance but at this stage you should exclude them They are nondecomposable An attribute can contain only single values never lists or repeating groups Composite values must be broken into separate attributes They contain data of the same type For example you would want to enter only date values in a birthday attribute not names or telephone numbers The rules for defining attributes are the same as those for defining columns For more information about defining columns see Placing Constraints on Columns on page 8 21 The following attributes are added to the telephone directory example to produce the diagram shown in Figure 8 10 on page 8 19 Street city state and zip code are added to the address entity Birth date is added to the name entity Also added to the name entity are e mail address anniversary date and children s first names Typ
448. nality 13 19 The Cost of Network Access 13 20 The Importance of Table Order 13 22 Making Queries Faster 13 27 Preparing a Test Environment 13 28 Studying the Data Model 13 28 Studying the Query Plan 13 29 Examining the Indexes 13 29 Refining the Column Filters 13 31 Rethinking the Query 13 33 Reviewing the Optimization Level 13 36 Using a Temporary Table to Speed Queries 13 36 Summary 13 41 Chapter 14 Chapter 15 Creating and Using Stored Procedures Chapter Overview 14 3 Introduction to Stored Procedures and SPL 14 3 What You Can Do with Stored Procedures 14 3 Relationship Between SQL and a Stored Procedure 14 4 Creating and Using Stored Procedures 14 4 Creating a Procedure Using DB Access 14 5 Creating a Procedure Using an SQL API 14 5 Commenting and Documenting a Procedure 14 6 Diagnosing Compile Time Errors 14 6 Looking at Compile Time Warnings 14 8 Generating the Text or Documentation 14 8 Executing a Procedure 14 9 Executing a Stored Procedure Dynamically 14 11 Debugging a Procedure 14 11 Re creating a Procedure 14 13 Privileges on Stored Procedures 14 13 Privileges Necessary at Creation 14 14 Privileges Necessary at Execution 14 14 Revoking Privileges 14 16 Variables and Expressions 14 16 Variables 14 16 SPL Expressions 14 21 Program Flow Control 14 22 Branching 14 22 Looping 14 23 Function Handling 14 24 Passing Information into and out of a Procedure 14 25 Returning Results 14 25 Exception Handling 14 27
449. name bdate anniv email enia child2 child3 repeating columns Unnormalized name entity Some problems can be noted in the current table Space is always reserved on the disk for three child records whether the person has children or not The maximum number of children that you could record is three but some of your acquaintances might have four or more children If you look for a particular child you would have to search all three columns in every row You can eliminate the repeating columns and bring the table to first normal form by separating the table into two tables as shown in Figure 8 15 Put the repeating columns into one of the tables The association between the two tables is established with a primary and foreign key combination Because a child cannot exist without an association in the name table we can reference the name table with a foreign key rec_num name rec_num iname fname bdate anniv email Primary Key TRG child rec_num child_name Foreign Key First normal form reached for name entity In addition the modem name relationship is not at first normal form because the columns b300 b1200 and b2400 are considered repeating columns This relationship is normalized in a similar manner as the name child relationship 8 30 Building Your Data Model Normalizing Your Data Model as shown in Figure 8 16 A b_type attribute is added to the entity
450. nd ALTER TABLE statements to create relationships between tables The ON DELETE CASCADE option of the REFERENCES clause allows you to delete rows from parent and associated child tables with one DELETE statement You use transactions to prevent unforeseen interruptions in a modification from leaving the database in an indeterminate state When modifications are performed within a transaction they are rolled back following an error The transaction log also extends the periodically made archive copy of the data base so that if the database must be restored it can be brought back to its most recent state Data replication which is transparent to users offers another type of protection from catastrophic failures Programming with SOL Chapter Overview 3 SQL in Programs 3 Static Embedding 5 Dynamic Statements 5 Program Variables and Host Variables 5 Calling the Database Server 8 The SQL Communications Area 8 The SQLCODE Field 11 End of Data 11 Negative Codes 11 The SQLERRD Array 12 The SQLAWARN Array 12 The SQLSTATE Value 12 Retrieving Single Rows 13 Data Type Conversion 14 Dealing with Null Data 15 Dealing with Errors 16 End of Data 17 Serious Errors 17 Using Default Values 17 End of Data with Databases that are not ANSI Compliant 18 Interpreting End of Data with Aggregate Functions 18 Retrieving Multiple Rows 19 Declaring a Cursor 20 Opening a Cursor 20 Fetching Rows 21 Detecting End of Data 21 Locating the
451. nd NY Chris Putnum Putnum s Putters Bartlesville OK Query Result 2 24 Using a WHERE Clause to Find a Subset of Values As shown in Excluding Rows on page 2 30 Query 2 25 also assumes the use of an ANSI compliant database The owner qualifier is in quotation marks to preserve the case sensitivity of the literal string SELECT lname city state phone FROM Aleta customer WHERE state AZ OR state NJ ORDER BY lIname SELECT lname city state phone FROM Aleta customer WHERE state IN AZ NJ ORDER BY lIname Query 2 25 Composing Simple SELECT Statements 2 33 Single Table SELECT Statements Each statement in Query 2 25 retrieves rows that include the subset of AZ or Nd in the state column of the Aleta customer table as shown in Query Result 2 25 lname city state phone Jewell Phoenix AZ 602 265 8754 Lessor Phoenix AZ 602 533 1817 O Brian Princeton NJ 609 342 0054 Shorter Cherry Hill NJ 609 663 6079 Query Result 2 25 Note that you cannot test a TEXT or BYTE column with the IN keyword In Query 2 26 an example of a query on an ANSI compliant database no quotation marks exist around the table owner name Whereas the two state ments in Query 2 25 searched the Aleta customer table Query 2 26 searches the table ALETA customer which is a different table due to how ANSI compliant databases look at owner names SELECT lname city state phone FROM Aleta customer WHERE st
452. nd one is error number 746 which allows you to supply the message text up to a maximum of 71 characters 15 14 Creating and Using Triggers Generating Error Messages Applying a Fixed Error Message You can apply error number 745 to any trigger failure that is not an SQL error The following fixed message is for this error 745 Trigger execution has failed You can apply this message with the RAISE EXCEPTION statement in SPL The following example generates error 745 if new_qty is greater than old_qty multiplied by 1 50 CREATE PROCEDURE upd_items_p2 DEFINE GLOBAL old_qty INT DEFAULT 0 DEFINE new_qty INT LET new_qty SELECT SUM quantity FROM items IF new_qty gt old_qty 1 50 THEN RAISE EXCEPTION 745 END IF END PROCEDURE If you are using DB Access the text of the message for error 745 displays on the bottom of the screen as seen in Figure 15 4 SQL New Run Modify Use editor Output Choose Save Info Drop Exit Modify the current SQL statements using the SQL editor stores6 myserver Press CTRL W for Help INSERT INTO items VALUES 2 1001 2 HRO 1 126 00 745 Trigger execution has failed Figure 15 4 Error message 745 with fixed message Creating and Using Triggers 15 15 Generating Error Messages If you trigger the erring procedure through an SQL statement in your SQL API the database server sets the SQL error status variable to 745 and return
453. nda manatee 4 260 zenda manatee 105 274 zenda manatee 106 1025 zenda manatee 107 1026 zenda manatee 108 1027 zenda manatee 109 1028 zenda manatee 110 1029 zenda Query Result 3 20 Note that you should never store a rowid in a permanent table or attempt to use it as a foreign key because the rowid can change For example if a table is dropped and then reloaded from external data all the rowids are different USER and DBSERVERNAME were discussed in Chapter 2 Composing Sim ple SELECT Statements Outer Joins Chapter 2 Composing Simple SELECT Statements showed how to create and use some simple joins Whereas a simple join treats two or more joined tables equally an outer join treats two or more joined tables unsymmetrically It makes one of the tables dominant also called preserved over the other subservient tables Outer joins occur in four basic types e A simple outer join on two tables e A simple outer join to a third table e An outer join for a simple join to a third table e An outer join for an outer join to a third table This section discusses these types of outer joins See the discussion of outer joins in Chapter 1 of the Informix Guide to SQL Syntax for full information on their syntax use and logic Composing Advanced SELECT Statements 3 21 Creating Advanced Joins In a simple join the result contains only the combinations of rows from the tables that satisfy the join conditions
454. ndependence of 1 117S phantom 1 367S retrieving with FETCH 1 197S rowid definition 1 197S size of fixed length 10 13T updating through a view 1 384S writing buffered rows with FLUSH 1 2045 ROW keyword use in ALTER TABLE 1 338 use in CREATE TABLE 1 108S Row lock 7 8T Rowid locating internal row numbers 3 17T use in a column expression 1 435S use in a join 3 16T use in ORDER BY clause 1 3385 used as column name 1 474S Rowid function 13 18T ROWID keyword 1 435S Rules for stored procedures 1 1285 Run time program setting DBANSIWARN 4 15R setting INFORMIXCOBDIR 4 32R S SCALE field setting with SET DESCRIPTOR 1 3585 with GET DESCRIPTOR 1 214S Schema See Data Model Scroll cursor active set 5 25T definition of 1 149S 5 23T use of 1 149S with FETCH 1 196S with hold in a transaction 1 369S SCROLL keyword syntax in DECLARE 1 145S Index 37 38 Index use in DECLARE 1 1495 5 23T Search condition See Condition segment secheck utility 13 31T SECOND keyword syntax in DATETIME data type 1 428S in INTERVAL data type 1 485S use as DATETIME field qualifier 3 8R 1 488S as INTERVAL field qualifier 3 14R 1 491S Second normal form 8 31T Secondary site 12 20T Security constraining inserted values 11 20T 11 25T database level privileges 11 5T making database inaccessible 11 5T restricting access to columns 11 20T restricting access to rows 11 20T 11 21T restricting access to view 11 27T table level privi
455. ndexing of data containing foreign characters can cause significant performance degradation for certain data sets If you do not need the functionality of NLS for all your character data Informix recommends that you use the CHAR data type instead of NCHAR or VARCHAR instead of NVARCHAR for character columns whenever possible Because CHAR and VARCHAR data require simple value based comparison sorting and index ing the cost of CHAR or VARCHAR columns is thus relatively less expensive than NCHAR or NVARCHAR columns Optimizing Your Queries 13 19 Time Costs of a Query The Structure of an Index An index is arranged as a hierarchy of pages technically a B tree as depicted in the figure below At the bottom level a sequence of leaf pages contains the index key values of the table rows each with a pointer to the location of the row containing that value The keys in the leaf pages are in key sequence At each higher level a page lists the highest key value to be found in each page at the lower next level The topmost level is a single root page from which any other page of the index can be found root page leaf page leaf page The size of one entry is the width of the indexed columns in bytes plus 4 If you know that and the page size you can estimate the number of entries per page This estimate is approximate because first some data c
456. ne machine e A simple network connection e Multiple connections on a network e Data managed by non Informix database servers INFORMIX TP XA It is not enough to simply build a computer network you have to re examine how your applications and database servers share data This chapter also covers the following topics concerned with managing data shared over a network e Distributed data Connecting to data e Protecting Your data e Synonym chains e Network transparency The final sections of the chapter discuss protecting your data in a networked environment Understanding Informix Networking 12 3 What Is a Network What Is a Network A computer network is a group of computers workstations and other devices connected together over some kind of communications system to share resources and data A network site is simply the location of one of the com puters on the network Sometimes the network sites are widely separated but they may also be in the same room or building Two network sites can even coexist on the same machine To make a practical computer network work you must master a multitude of technical details regarding hardware and software There are far too many of these details and they change too fast to cover them in this book This chap ter gives a conceptual discussion of some of the issues that you will encounter when you use a computer network For more information refer to the man ual that accompan
457. neck Tables 35 Summary 36 10 2 Tuning Your Data Model Chapter Overview The preceding chapters summarized the steps of creating and implementing a data model that is theoretically sound Normally the resulting database also yields adequate performance If it does the job is done However some applications have more stringent performance requirements Some databases contain extremely large tables others must be usable by many programs concurrently or by programs that operate under tight requirements for response time and others must be extremely reliable You can tune your database design to meet such requirements In some cases you might have to sacrifice theoretical correctness in the data model to get the performance you need Before you make any changes however make sure that the queries are as efficient as possible Study Chapter 13 Optimizing Your Queries to see what you can do to improve performance without changing the data model The remainder of this chapter contains discussions on the following topics The disk storage methods used by INFORMIX OnLine Dynamic Server and their implications for performance and reliability The methods for calculating the sizes of tables and indexes and using those numbers to estimate query execution time e The benefits and costs of adding indexes e The ways you can denormalize the data model that is spoil its theoretical purity to improve performance e Sugg
458. ned by the user odin the value in the state column should not be equal to CA customer_num company city state 119 The Triathletes Club Cherry Hill NJ 120 Century Pro Shop Phoenix AZ 121 City Sports Wilmington DE 122 The Sporting Life Princeton NJ 123 Bay Sports Jacksonville FL 124 Putnum s Putters Bartlesville OK 125 Total Fitness Sports Brighton MA 126 Neelie s Discount Sp Denver CO 127 Big Blue Bike Shop Blue Island NY 128 Phoenix College Phoenix AZ Query Result 2 22 Specifying Rows Query 2 23 shows two ways to specify rows in a WHERE clause SELECT catalog_num stock_num FROM catalog SELECT catalog_num stock_num FROM catalog manu_code manu_code WHERE catalog_num BETWEEN 10005 AND 10008 cat_advert cat_advert WHERE catalog_num gt 10005 AND catalog_num lt 10008 Query 2 23 Composing Simple SELECT Statements 2 31 Single Table SELECT Statements 2 32 Each statement in Query 2 23 specifies a range for catalog_num from 10005 through 10008 inclusive The first statement uses keywords and the second uses relational operators to retrieve the rows shown in Query Result 2 23 catalog_num stock_num manu_code cat_advert catalog_num stock_num manu_code cat_advert te catalog_num stock_num manu_code cat_advert catalog_num stock_num manu_code cat_advert 10005 3 HSK High Technology Design Expands the Sweet Spot 10006 3 SHM Durabl
459. nformix Guide to SQL Syntax This section discusses the use of CREATE DATABASE and CRE ATE TABLE in implementing a data model The use of CREATE INDEX is covered in the next chapter 9 20 Implementing Your Data Model Creating the Database Keep in mind that the telephone directory data model is used for illustrative purposes only For the sake of the example we translate it into SQL statements You might have to create the same database model more than once However the statements that create the model can be stored and executed automati cally See Using Command Scripts on page 9 26 for more information about using this topic When the tables exist you must populate them with rows of data You can do this manually with a utility program or with custom programming Using CREATE DATABASE A database is a container that holds all the parts that go into a data model These parts include not only the tables but also views indexes synonyms and other objects associated with the database You must create a database before you can create anything else Besides creating the database the CRE ATE DATABASE statement establishes the kind of transaction logging to be used Transaction logging is discussed in Chapter 4 Modifying Data The INFORMIX OnLine Dynamic Server database server differs from other database servers in the way that it creates databases and tables OnLine is discussed first Using CREATE DATABASE wi
460. ng example show a sequential cursor declared in INFORMIX ESQL C EXEC SQL DECLARE pcurs CURSOR FOR SELECT customer_num lname city FROM customer After it is opened the cursor can be used only with a sequential fetch that retrieves the next row of data as shown in the following example EXEC SQL FETCH p_curs INTO cnum clname ccity Each sequential fetch returns a new row A scroll cursor is declared with the keyword SCROLL as shown in the following example from INFORMIX ESQL FORTRAN EXEC SQL DECLARE s_curs SCROLL CURSOR FOR SELECT order_num order_date FROM orders WHERE customer_num gt 104 A scroll cursor can be used with a variety of fetch options The ABSOLUTE option specifies the rank number of the row to fetch EXEC SQL FETCH ABSOLUTE numrow s_curs INTO nordr nodat This statement fetches the row whose position is given in the host variable numrow It is also possible to fetch the current row again or to fetch the first row and then scan through the entire list again However these features are obtained at a price as described in the next section Programming with SQL 5 23 Retrieving Multiple Rows The Active Set of a Cursor Once a cursor is opened it stands for some selection of rows The set of all rows that the query produces is called the active set of the cursor It is easy to think of the active set as a well defined collection of rows and to think of the
461. ng real data and check its size with the oncheck utility Variable Estimate Basis for Estimate estrows 1 500 company business plan pagesize 2 048 output of onstat pageuse 2 016 pagesize keysize 4 customer_num is 4 bytes petuniq 1 0 unique index entsize 12 4 5 1 pagents 168 floor 2 016 12 leaves 9 ceiling 1 500 168 branches 1 ceiling 9 168 keysize 2 state is CHAR 2 petuniq 0 033 50 states among 1 500 rows entsize 8 066 2 5 0 033 pagents 249 floor 2 016 8 066 leaves 7 ceiling 1 500 249 branches 1 ceiling 7 168 Estimating the size of two indexes from the customer table Estimating Blobpages BYTE and TEXT data items that are stored on magnetic disk are stored in separate pages either interspersed among the row and index pages in the tblspace or in a separate blobspace This discussion does not apply to blob data stored on optical media Each blob data item occupies a whole number of pages For each blob column let the values be as shown in the following list typage the number of whole pages required to store an item of typical size nnpart the fraction of rows in which this column has a non null value totpage typage x estrows x nnpart Tuning Your Data Model 10 17 Calculating Table Sizes The values for the column occupy approximately totpage pages In the catalog table see Figure 10 6 on page 10 14 two blobpages occur Their estimates can be imagined as described in the follow
462. ng system When access to the data is serialized so that only one program at a time can use it processing slows dramatically Locking and Integrity Unless controls are placed on the use of data concurrency can lead to a variety of negative effects Programs can read obsolete data or modifications can be lost even though they were apparently completed The database server prevents errors of this kind by imposing a system of locks A lock is a claim or reservation that a program can place on a piece of data The database server guarantees that as long as the data is locked no other program can modify it When another program requests the data the database server either makes the program wait or turns it back with an error Locking and Performance Because a lock serializes access to one piece of data it reduces concurrency any other programs that want access to that data must wait The database server can place a lock on a single row a disk page which holds multiple Programming for a Multiuser Environment 7 3 Concurrency Issues rows a whole table or an entire database The more locks it places and the larger the objects it locks the more concurrency is reduced The fewer the locks and the smaller the objects the greater concurrency and performance can be This section discusses how a program can achieve two goals e To place all the locks needed to ensure data integrity To lock the fewest smallest pieces of dat
463. ngle row A simple join combines information from two or more tables based on the relationship between one column in each table A composite join is a join between two or more tables based on the relationship between two or more columns in each table To create a join you must specify a relationship called a join condition between at least one column from each table Because the columns are being compared they must have compatible data types When you join large tables performance improves when you index the columns in the join condition Data types are described in Chapter 3 of the Informix Guide to SQL Reference and indexing is discussed in Chapter 10 Tuning Your Data Model and Chapter 13 Optimizing Your Queries Creating a Cartesian Product When you perform a multiple table query that does not explicitly state a join condition among the tables you create a Cartesian product A Cartesian prod uct consists of every possible combination of rows from the tables This is usually a very large unwieldy result and the data is inaccurate Query 2 71 selects from two tables and produces a Cartesian product SELECT FROM customer state Query 2 71 Composing Simple SELECT Statements 2 69 Multiple Table SELECT Statements Although only 52 rows exist in the state table and 28 rows in the customer table the effect of Query 2 71 is to multiply the rows of one table by the rows of the other and retrieve an
464. ns 14 21T naming output file for TRACE statement 1 351S owner privileged 1 1295 14 13T privileges 1 129S privileges necessary at execution 14 14T program flow control 14 22T receiving data from SELECT 1 318S recursion 14 24T REFERENCES clause 14 18T returning values 14 25T revoking privileges on 1 3015 14 16T security purposes 11 3T simulating errors 2 365 tracing triggered actions 15 12T use 14 3T variable 14 16T Stored Procedure Language See SPL stores6 database call_type table columns A 5R catalog table columns A 4R copying Intro 10R Intro 135S 8T creating Intro 10R Intro 135S 8T customer table columns A 2R cust_calls table columns A 5R data values A 15R description of A 1R items table columns A 3R manufact table columns A 5R map of A 6R orders table columns A 3R overview Intro 9R Intro 12S 7T primary foreign key relationships A 8R to A 15R state table columns A 6R stock table columns A 4R structure of tables A 2R Structured Query Language See SQL Subquery beginning with ALL ANY SOME keywords 1 330S beginning with EXISTS keyword 1 330S beginning with IN keyword 1 329S correlated 1 4135 3 32T 4 22T 13 32T definition of 1 326S in Condition segment 1 413S in DELETE statement 4 6T in SELECT 3 32T to 3 42T in UPDATE SET 4 13T in UPDATE WHERE 4 12T performance of 13 32T restrictions with UNION operator 1 344S with DISTINCT keyword 1 313S See also Condition segment Subscripting in a
465. ns in the syscolumns system catalog table in estimating the number of rows returned by each part of a WHERE clause When using data distribution statistics for the first time try updating statistics in MEDIUM mode on all tables followed by updating statistics in HIGH mode on columns that head indexes This will produce single table query estimates that on the average have an error less than 2 5 percent of the total number of rows in the table For columns with HIGH mode distributions the default resolution is 1 0 percent Optimizing Your Queries 13 29 Making Queries Faster Unless column values change by a considerable margin it is unnecessary to regenerate data distributions You can verify the accuracy of the distribution by comparing dbschema hd option output with appropriately constructed SELECT statements For additional information about data distributions and the UPDATE STATISTICS statement see Chapter 1 of the Informix Guide to SQL Syntax Filter Selectivity Assignments The following table lists some of the selectivities that the optimizer assigns to filters of different types It is not an exhaustive list and other expression forms may be added in the future Expression Form indexed col literal value indexed col host variable indexed col IS NULL tab1 indexed col tab2 indexed col indexed col gt literal value indexed col lt literal value any col IS NULL any col any expression any col gt a
466. ns instead of their CHAR or VARCHAR counterparts The NCHAR and NVARCHAR data types allow foreign characters in character data For additional information on these and other data types see Chapter 9 Implementing Your Data Model in this manual and Chapter 3 in the Informix Guide to SQL Reference Single Table SELECT Statements You can query a single table in a database in many ways You can tailor a SELECT statement to perform the following actions e Retrieve all or specific columns Retrieve all or specific rows Perform computations or other functions on the retrieved data Order the data in various ways Composing Simple SELECT Statements 2 11 Single Table SELECT Statements Selecting All Columns and Rows The most basic SELECT statement contains only the two required clauses SELECT and FROM Using the Asterisk Query 2 5a specifies all the columns in the manufact table in a select list A select list is a list of the column names or expressions that you want to project from a table SELECT manu_code manu_name lead_time FROM manufact Query 2 5a Query 2 5b uses the wildcard asterisk which is shorthand for the select list The represents the names of all the columns in the table You can use the when you want all the columns in their defined order SELECT FROM manufact Query 2 5b Query 2 5a and Query 2 5b are equivalent and display the same results that is a list of
467. nships You must consider every pair of entities A and B and ask What is the relationship between an A and a B A relationship is an association between two entities Usually a verb or preposition connecting two entities will imply a relationship A relationship between entities is described in terms of connectivity existence dependency and cardinality Connectivity Connectivity refers to the number of entity instances An entity instance is a particular occurrence of an entity The three types of connectivity are one to one written 1 1 one to many written 1 n and many to many written m n shown graphically in Figure 8 2 8 8 Building Your Data Model Figure 8 2 Identifying and Defining Your Principal Data Objects a Sy ZX aS one to one one to many many to many Connectivity in relationships For example in the telephone directory example an address can be associated with more than one name The connectivity for the relationship between the name and address entities is one to many 1 n Existence Dependency Cardinality Existence dependency describes whether an entity in a relationship is optional or mandatory Analyze your business rules to identify whether an entity must exist in a relationship For example your business rules may dic tate that an address must be associated with a name This would make
468. nt of SQLERRD to show how many rows they affected this topic is covered in Chapter 6 Modifying Data Through SQL Programs Interpreting End of Data with Aggregate Functions A SELECT statement that selects an aggregate function such as SUM MIN or AVG always succeeds in returning at least one row of data This is true even when no rows satisfy the WHERE clause an aggregate value based on an empty set of rows is null but it exists nonetheless However an aggregate value is also null if it is based on one or more rows that all contain null values If you must be able to detect the difference between an aggregate value based on no rows and one based on some rows that are all null you must include a COUNT function in the statement and an indicator variable on the aggregate value You can then work out the following three cases Count Value Indicator Case 0 1 zero rows selected gt 0 1 some rows selected all were null gt 0 0 some non null rows selected The previous example deals with the following considerations e Ifthe query selects some non null rows the correct value is returned and used This is the expected and most frequent result e Ifthe query selects no rows or in the much less likely event that it selects only rows that have null values in the total_price column a column that should never be null the indicator variable is set and the default value is assigned e Ifany serious error occurs the host va
469. ntax 1 113S Triggered action action on triggering table 1 127S anyone can use 1 1295 BEFORE and AFTER 15 7T cascading 1 118S clause 1 1215 action statements 1 1225 syntax 1 1215 WHEN condition 1 121S correlation name in 1 125S 1 128S FOR EACH ROW 15 8T generating an error message 15 14T in client server environment 1 133S in relation to triggering statement 15 6T list AFTER 1 117S BEFORE 1 116S FOR EACH ROW 1 116S for multiple triggers 1 117S sequence of 1 116S merged 1 117S preventing overriding 1 1325 statements 15 3T tracing 15 12T using 15 7T using stored procedures 15 10T WHEN condition 1 1215S 15 10T Triggering statement affecting multiple rows 1 117S execution of 1 113S guaranteeing same result 1 112S result of 1 1235 UPDATE 1 115S Triggering table action on 1 127S and cascading triggers 1 131S Trigonometric function ACOS function 1 460S ASIN function 1 460S ATAN function 1 460S ATAN2 function 1 461S COS function 1 459S SIN function 1 459S TAN function 1 460S TRUNC function syntax in expression 1 4445 use in expression 1 447S Truncation signalled in SQLAWARN 5 12T Two phase commit 12 20T TYPE field changing from BYTE or TEXT 1 359S setting in SET DESCRIPTOR 1 356S setting in X Open programs 1 357S with X Open programs 1 213S Typographical conventions Intro 5R Intro 5S 5T U Unbuffered logging 9 22T Underscore _ wildcard in Condition segment 1 410S UNION operator description of 3 43T displa
470. ntire table One example might be a table that contains a large mailing list If you find that a postal code column is often used to filter a subset of rows you should consider putting an index on it even though it is not used in joins This strategy yields a net savings of time only when the selectivity of the column is high that is when only a small fraction of rows holds any one indexed value Nonsequential access through an index takes several more disk I O operations than sequential access does so if a filter expression on the column passes more than a fourth of the rows the database server might as well read the table sequentially As a rule indexing a filter column saves time in the following cases The column is used in filter expressions in many queries or in slow queries The column contains at least 100 unique values Most column values appear in fewer than 10 percent of the rows Order By and Group By Columns When a large quantity of rows must be ordered or grouped the database server must put the rows in order One way the database server does this is to select all the rows into a temporary table and sort the table But as dis cussed in Chapter 13 Optimizing Your Queries if the ordering columns are indexed the optimizer sometimes plans to read the rows in sorted order through the index thus avoiding a final sort Because the keys in an index are in sorted sequence the index really represents the re
471. nts It sets SQLCODE to specify the type of statement that is the verb with which it begins If the prepared statement is a SELECT the DESCRIBE statement also returns information about the selected output data If the pre pared statement is an INSERT the DESCRIBE statement returns information about the input parameters The data structure is a predefined data structure allocated for this purpose and is known as a system descriptor area If you are using INFORMIX ESQL C you can use a system descriptor area or as an alternative an sqlda structure The data structure that a DESCRIBE statement returns or references for a SELECT statement includes an array of structures Each structure describes the data that is returned for one item in the select list The program can exam ine the array and discover that a row of data includes a decimal value a character value of a certain length and an integer Using this information the program can allocate memory to hold the retrieved values and put the necessary pointers in the data structure for the database server to use Freeing Prepared Statements A prepared SQL statement occupies space in memory With some database servers it can consume space owned by the database server as well as space belonging to the program This space is released when the program terminates but in general you should free this space when you finish with it You can use the FREE statement to release this space It takes
472. nts being executed For example the job of entering a new order in the stores6 database requires you to perform the following steps Insert a row in the orders table This generates an order number e For each item ordered insert a row in the items table Two ways to program an order entry application exist One way is to make it completely interactive so that the program inserts the first row immediately and then inserts each item as the operator enters data This is the wrong approach because it exposes the operation to the possibility of many more unforeseen events the customer s telephone disconnecting the operator pressing the wrong key the operator s terminal losing power and so on The right way to build an order entry application is described in the following list Accept all the data interactively e Validate the data and expand it by looking up codes in stock and manufact for example Display the information on the screen for inspection e Wait for the operator to make a final commitment e Perform the insertions quickly Even when this is done sometimes an unforeseen circumstance can halt the program after it inserts the order but before it finishes inserting the items If that happens the database is in an unpredictable condition Its data integrity is compromised The Transaction The solution to all these potential problems is called the transaction A transaction is a sequence of modificat
473. nts them by setting different rules for how a program uses locks when it is reading This does not apply to reads performed on update cursors You set the isolation level using the command SET ISOLATION LEVEL All INFORMIX OnLine Dynamic Server database servers support this statement Programming for a Multiuser Environment 7 9 Setting the Isolation Level Dirty Read Isolation The simplest isolation level Dirty Read amounts to virtually no isolation When a program fetches a row it places no locks and it respects none it sim ply copies rows from the database without regard for what other programs are doing A program always receives complete rows of data even under Dirty Read isolation a program never sees a row in which some columns have been updated and some have not However a program using Dirty Read isolation sometimes reads updated rows before the updating program ends its trans action If the updating program later rolls back its transaction the reading program processed data that never really existed number 4 in the list of concurrency issues on page 7 5 Dirty Read is the most efficient level The reading program never waits and never makes another program wait It is the preferred level in any of the following cases e All tables are static that is concurrent programs only read and never modify data e The database is held in an exclusive lock e Itis certain that only one program is using the database
474. num called resolved 106 6 6 110 7 T 119 7 F 121 Gl 7 Query Result 2 57 Composing Simple SELECT Statements 2 59 Single Table SELECT Statements Using WEEKDAY In Query 2 58 the WEEKDAY function is used to indicate which day of the week calls are received and resolved 0 represents Sunday 1 is Monday and so on and the expression columns are labeled SELECT customer_num WEEKDAY call_dtime called WEEKDAY res_dtime resolved FROM cust_calls ORDER BY resolved Query 2 58 customer_num called resolved 127 110 119 121 116 106 TIG U WwW aH OW BwWWWDN O Query Result 2 58 Query 2 60 uses the COUNT and WEEKDAY functions to count how many calls were received on a weekend This kind of statement can give you an idea of customer call patterns or indicate whether overtime pay might be required SELECT COUNT FROM cust_calls WHERE WEEKDAY call_dtime IN 0 6 Query 2 59 count Query Result 2 59 2 60 Composing Simple SELECT Statements Single Table SELECT Statements Query 2 60 retrieves rows where the call_dtime is earlier than the beginning of the current year SELECT customer_num call_code YEAR call_dtime call_year YEAR res_dtime res_year FROM cust_calls WHERE YEAR call_dtime lt YEAR TODAY Query 2 60 customer_num call_code call_year res_year 116 I 1992 1992 116 I 1992 1992 Query Result 2 60 Formatting DATETIME Values In Que
475. ny expression any col lt any expression any col MATCHES any expression any col LIKE any expression EXISTS subquery NOT expression expr1 AND expr2 expr1 OR expr2 any col IN list any col relop ANY subquery Key Selectivity F F 1 number of distinct keys in index F 1 number of distinct keys in the larger index F 2nd max literal value 2nd max 2nd min F literal value 2nd min 2nd max 2nd min F 1 10 F 1 3 F 1 5 F 1 if subquery estimated to return gt 0 rows else 0 F 1 F expression F F expr1 x F expr2 F F expr1 F expr2 F expr1 x F expr2 treated as anycol item OR OR anycol item treated as any col relop value OR OR anycol relop valuen for estimated size of subquery n indexed col first or only column in an index OnLine only 2nd max 2nd min second largest and smallest key values in indexed column OnLine only any col any column not covered by a preceding formula Selectivities are more accurate with distributions than through current index information due to finer granularity statistics However if data distributions are not used filter selectivities are used as shown in the following chart 13 30 Optimizing Your Queries Making Queries Faster Using Composite Indexes The optimizer can use a composite index one that covers more than one column in several ways In addition to its usual function of ensuring that the values in columns abc a
476. obtain the current time as a DATETIME value A 4GL program can perform automated timing with code similar to that shown in the following example Oo EFINE start_time DATETIME HOUR TO FRACTION 2 elapsed INTERVAL MINUTE 4 TO FRACTION 2 LET start_time EXTEND CURRENT HOUR TO FRACTION 2 here perform the operation to be timed LET elapsed EXTEND CURRENT HOUR TO FRACTION 2 start_time DISPLAY Elapsed time was elapsed Elapsed time in a multiprogramming system or network environment where resources are shared among multiple processes does not always correspond to execution time Most C libraries contain a function that returns the CPU time of a program and C functions can be called from 4GL programs and ACE reports Finding the Guilty Functions In most programs a very small fraction of the code typically 20 percent or less accounts for the bulk of the program execution time typically 80 percent or more The 80 20 rule as it is called holds in most cases often the propor tions are even greater After you establish a timing mechanism use it to define the hot spots in the application that is the statements that consume most of the time In addition many computer systems provide profiling tools that can help determine the location of hot spots Keeping an Open Mind With embedded SQL in which one statement can trigger thousands of disk accesses it is possible that the guil
477. ocedure owner and any user with the DBA privilege Execute privilege and privileges on underlying objects If owner has privileges on underlying objects with the GRANT WITH option only the Execute privilege is required Figure 14 8 Differences between DBA privileged and owner privileged procedures Privileges Necessary at Creation Only users who have the DBA privilege can create a DBA privileged procedure To create an owner privileged procedure you need to have at least the Resource privilege See Granting and Limiting Access to Your Data base on page 11 3 Privileges Necessary at Execution To run a procedure you always need the Execute privilege for that procedure or DBA database privileges Depending on whether the procedure is a DBA mode procedure and if the database is ANSI compliant certain privileges are granted to users implicitly by the database server If the procedure is owner privileged the database server grants the Execute privilege to PUBLIC If the database is ANSI compliant the database server grants only the Execute privilege to the owner and users with DBA status If the procedure is DBA privileged the database server grants the Execute privilege to all users having the DBA privilege 14 14 Creating and Using Stored Procedures Privileges on Stored Procedures Owner Privileged Procedures When you execute an owner privileged procedure the database server checks the existence of any re
478. ode call_dtime res_dtime call_dtime span FROM cust_calls ORDER BY span Query 2 43 Query 2 43 retrieves the same data from the cust_calls table as Query 2 42 In Query 2 43 the ORDER BY clause causes the data to be displayed in ascending order of the derived values in the span column as shown in Query Result 2 43 customer_num user_id call_code call_dtime span 127 maryj aE 1993 07 31 14 30 121 maryj O 1993 07 10 14 05 0 00 01 106 maryj D 1993 06 12 08 20 0 00 05 110 riche L 1993 07 07 10 24 0 00 06 116 mannyn I 1992 11 28 13 34 0 03213 119 riche B 1993 07 01 15 00 0 17521 116 mannyn T 1992 12 21 11 24 5 20 55 Query Result 2 43 Query 2 44 uses an integer to represent the result of the operation res_dtime call_dtime and retrieves the same rows that appear in Query Result 2 43 SELECT customer_num user_id call_code call_dtime res_dtime call_dtime span FROM cust_calls ORDER BY 5 Query 2 44 2 52 Composing Simple SELECT Statements Single Table SELECT Statements Using Functions in SELECT Statements In addition to column names and operators an expression also can include one or more functions Expressions supported include aggregate function which include arithmetic functions constant and column expressions These expressions are described in Chapter 1 of the Informix Guide to SQL Syntax Aggregate Functions The aggregate functions are COUNT AVG MAX MIN and SUM They take on values
479. oded in system catalog 2 28R 2 32R 11 9T Execute 11 12T 14 14T for triggered action 1 129S granting 11 5T to 11 15T Index 1 236S 11 8T Insert 1 2365 11 8T 11 28T needed to create a view 1 239S 11 27T to drop an index 1 1745 to modify data 1 236S 4 15T on a synonym 1 805 on a view 1 137S 11 28T on stored procedures 14 13T overview 1 8T Resource 1 233S 11 7T 13 34T Select 11 8T 11 10T 11 27T Update 1 236S 11 8T 11 10T 11 28T when privileges conflict 1 232S with DBA privileged procedures 14 13T with owner privileged procedures 14 13T See also Database level privilege See also Table level privilege PRIVILEGES FOR keywords in INFO statement 1 243S PRIVILEGES keyword syntax in GRANT 1 235S in REVOKE 1 301S use in GRANT 1 236S in REVOKE 1 302S Procedure cursor opening 1 265S reopening 1 2675 procedure cursor 1 148S Procedure name conflict with function name 1 495S naming conventions 1 495S Procedure stored See Stored procedure Processing distributed 12 8T Projection described 2 7T Project description of 1 13T Promotable lock 1 152S 7 6T 7 9T PSORT_DBTEMP environment variable 4 40R PSORT_NPROCS environment variable 4 41R PUBLIC keyword privilege granted to all users 11 6T syntax in GRANT 1 231S in REVOKE 1 300S use in GRANT 1 234S in REVOKE 1 302S PUT statement constant data with 6 11T count of rows inserted 6 11T impact on trigger 1 1125 sends returned data to buffer 6 10T source of row val
480. odel telephone directory example 8 6T Data protection with OnLine 12 19T Data replication 12 19T Data type automatic conversions 5 15T BYTE 3 5R 9 19T changing with ALTER TABLE 1 285 CHAR 3 6R 9 15T CHARACTER 3 7R character data 9 15T CHAR mapping to NCHAR 4 46R choosing 9 19T chronological 9 12T considerations for INSERT 1 2515S 1 498S conversion 3 23R 4 8T DATE 3 7R 9 12T DATETIME 3 7R 9 12T DEC 3 10R DECIMAL 3 10R 9 10T DOUBLE PRECISION 3 12R fixed point 9 10T FLOAT 3 12R floating point 3 12R 9 9T in SPL variables 14 17T INT 3 13R INTEGER 3 13R 9 7T INTERVAL 3 13R 9 14T MONEY 3 16R 9 10T NCHAR 3 17R NCHAR mapping to CHAR 4 46R NUMERIC 3 18R numeric 9 7T NVARCHAR 3 18R REAL 3 19R 9 9T requirements for referential constraints 1 22S 1 96S segment 1 4245 SERIAL 3 19R 9 7T SMALLFLOAT 3 20R 9 9T SMALLINT 3 20R specifying with CREATE VIEW 1 137S summary table 3 4R syntax 1 425S TEXT 3 21R 9 17T VARCHAR 3 22R 9 15T See also Data Type segment Data types creating NCHAR columns 1 19R creating NVARCHAR columns 1 19R OnLine specific 1 4R Database ANSI compliant 1 15T application 1 16T archiving 1 10T closing with CLOSE DATABASE 1 415 concurrent use 1 8T creating ANSI compliant 1 376S creating in NLS mode 1 20R creating with CREATE DATABASE 1 575 data types 3 4R default isolation levels 1 368S defined 1 3T 1 11T dropping 1 172S implicit connection 1 168S lock 1 1425 management of 1 9T ma
481. ol such as INFORMIX 4GL or an SQL application programming interface API such as INFORMIX ESQL C or the DB Access database access utility which is shipped as part of your database server The application development tool SQL API or DB Access enables you to compose queries send them to the database server and view the results that the database server returns You can use DB Access to try out all the SQL statements described in this guide Preface iii Summary of Chapters The Informix Guide to SQL Tutorial includes the following chapters iv Preface This Preface provides general information about the book and lists additional reference materials that can help you understand relational database management The Introduction tells how SQL fits into the Informix family of products and books explains how to use this book introduces the demonstration database from which the product examples are drawn and lists the new features for Version 6 0 of Informix database server products Part I Using Basic SQL This part contains introductory chapters on how to use SQL Read these chapters first if you are new to databases and SQL Chapter 1 Introducing Database Features and SQL contains an overview of database terminology and defines some important terms and ideas that are used throughout the book Chapter 2 Composing Simple SELECT Statements begins the exploration of making simple queries to retrieve and
482. ollowing 17 rows stock_num manu_code unit_price 102 PRC 480 00 102 SHM 220 00 106 PRC 23 00 107 PRC 70 00 108 SHM 45 00 112 SHM 549 00 113 SHM 685 90 203 NKL 670 00 305 HRO 48 00 308 PRC 280 00 310 ANZ 84 00 310 SHM 80 00 311 SHM 48 00 312 HRO 72 00 312 SHM 96 00 313 ANZ 60 00 313 SHM 72 00 Query Result 3 43 Summary This chapter was built on concepts introduced in Chapter 2 Composing Simple SELECT Statements It provided sample syntax and results for more advanced kinds of SELECT statements which are used to perform a query on a relational database This chapter Introduced the GROUP BY and HAVING clauses which can be used with aggregates to return groups of rows and apply conditions to those groups Described how to use the rowid to retrieve internal record numbers from tables and system catalog tables and discussed the serial internal table identifier or tabid Showed how to join a table to itself with a self join to compare values in a column with other values in the same column and to identify duplicates e Introduced the keyword OUTER explained how an outer join treats two or more tables asymmetrically and provided examples of the four kinds of outer join 3 54 Composing Advanced SELECT Statements Summary Described how to create correlated and uncorrelated subqueries by nesting a SELECT statement in the WHERE clause of another SELECT statement and showed the use
483. olumns that are nontransitively dependent on the primary key When you follow these rules the tables of the model are in what E F Codd the inventor of relational databases calls third normal form When tables are not in third normal form either redundant data exists in the model or problems exist when you attempt to update the tables If you cannot find a place for an attribute that observes these rules then you have probably made one of the following errors The attribute is not well defined The attribute is derived not direct The attribute is really an entity or a relationship 8 32 Building Your Data Model Summary Summary Some entity or relationship is missing from the model This chapter summarized and illustrated the following steps of entity relationship data modeling 1 Identify and define your principal data objects including the following options e Entities Relationships e Attributes 2 Diagram your data objects using the entity relationship diagram approach 3 Translate your entity relationship data objects into relational constructs Determine the primary and foreign keys for each entity 4 Resolve your relationships particularly the following relationships e 1 1 relationships mn relationships Other special relationships 5 Normalize your data model in one of the following forms e First normal form e Second normal form e Third normal form When the process is
484. om index 13 10T 13 31T optimizer uses 13 10T 13 23T selectivity estimates 13 30T finding location of row 1 435S FIRST keyword syntax in FETCH 1 1945 use in FETCH 1 196S First normal form 8 29T Fixed point 9 10T FLOAT data type changing data types 3 23R description of 3 12R 9 9T syntax 1 425S using as default value 1 195 1 895 Floating point 9 9T FLUSH statement count of rows inserted 6 11T syntax 1 204S with concatenation operator 1 4325 writing rows to buffer 6 10T FOR EACH ROW action SELECT statement in 1 117S triggered action list 1 116S FOR EACH ROW action See also FOREACH keyword FOR keyword in CONTINUE 2 65 in CREATE AUDIT 1 555 in CREATE SYNONYM 1 805 in EXIT 2 145 for locating temporary tables 1 100S FOR statement looping in a stored procedure 14 23T specifying multiple ranges 2 18S syntax 2 16S using expression lists 2 18S using increments 2 175 FOR TABLE keywords in UPDATE STATISTICS 1 393S FOR UPDATE keywords conflicts with ORDER BY 6 8T not needed in ANSI compliant database 6 16T relation to UPDATE 1 390S specific columns 6 16T syntax in DECLARE 1 145S use in DECLARE 1 1485 1 152S 1 155S in SELECT 1 340S with column list 1 153S FOREACH keyword in CONTINUE statement 2 65 in EXIT 2 14S FOREACH keyword See also FOR EACH ROW action FOREACH statement looping in a stored procedure 14 23T syntax 2 20S Foreign characters using NLS 1 14R Foreign key 1 225 1 935 1 945 4 19T See also Referential con
485. ome time before it issues the UPDATE or DELETE statement or it can simply fetch the next row When it is time to modify a row the database server obtains an exclusive lock on the row If it already had a promotable lock it changes it to exclusive status The duration of an exclusive row lock depends on whether transactions are in use If they are not in use the lock is released as soon as the modified row is written to disk When transactions are in use all such locks are held until the end of the transaction This prevents other programs from using rows that might be rolled back to their original state When transactions are in use a key lock is used whenever a row is deleted This prevents the following error from occurring Program A deletes a row Program B inserts a row having the same key e Program A rolls back its transaction forcing the database server to restore its deleted row What is to be done with the row inserted by program B By locking the index the database server prevents a second program from inserting a row until the first program commits its transaction The locks placed while reading a row are controlled by the current isolation level which is discussed in the next section Setting the Isolation Level The isolation level is the degree to which your program is isolated from the concurrent actions of other programs INFORMIX OnLine Dynamic Server offers a choice of four isolation levels It impleme
486. ompression is used in storing keys and second not all pages are full The number of levels depends on the number of rows to be indexed and the number of entries per page Suppose a page holds 100 keys Then a table of 100 rows has a single index page the root page A table with between 101 and 10 000 rows has a two level index consisting of a root page and from 2 to 100 leaf pages A table with as many as 1 000 000 rows has only a 3 level index so the preceding index must belong to a table of considerable size The Cost of Network Access Wherever data is moved over a network additional delays are imposed Networks are used in the following contexts The application sends a query across the network to a database server in another machine The database server performs the query using its locally 13 20 Optimizing Your Queries Time Costs of a Query attached disk The output rows are returned over the network to the application e Using the distributed data capability of INFORMIX OnLine Dynamic Server a database server in one machine can read and update rows from tables in databases located on other machines The data sent over a network consists of command messages and buffer sized blocks of row data Although many differences of detail exist between the two contexts they can be treated identically under a simple model in which one machine the sender sends a request to another the responder which responds with a block o
487. on the row and the entity on the column To repeat the fol lowing kinds of relationships are possible One to one written 1 1 in which never more than one entity A exists for one entity B and never more than one B for one A One to many written 1 n in which never more than one entity A exists but there can be several entities B related to it or vice versa Many to many written m n in which several entities A can be related to one B and several entities B can be related to one A One to many relationships are the most common Examples of one to many and many to many relationships are shown in the telephone directory model As you can see in Figure 8 4 the first unfilled cell represents the relationship between names and addresses What connectivity lies between these entities You can ask yourself how many names can be associated with an address Building Your Data Model 8 11 Identifying and Defining Your Principal Data Objects A name you decide can have zero or one address but no more than one You write 0 1 opposite name and below address as shown in the following figure name address name none 0 1 gt Ask yourself how many addresses can be associated with a name You decide that an address can be associated with more than one name For example you can know several people at one company or more than two people who live at the same address Can an address be associa
488. ond 6 second to second 2 month to fraction f 6 f 2 second to fraction f 2 f 2 day to day 2 fraction to fraction f 1 f 2 When fis odd round the size to the next full byte All possible precisions of the DATETIME data type with their sizes in bytes Implementing Your Data Model 9 13 Defining the Domains Figure 9 4 Durations INTERVAL The INTERVAL data type stores a duration that is a length of time The difference between two DATETIME values is an INTERVAL which represents the span of time that separates them The following examples might help to clarify the differences e Anemployee began working on January 21 1993 either a DATE ora DATETIME She has worked for 254 days an INTERVAL the difference between the TODAY function and the starting DATE or DATETIME She begins work each day at 0900 hours a DATETIME She works 8 hours an INTERVAL with 45 minutes for lunch another INTERVAL Her quitting time is 1745 hours the sum of the DATETIME when she begins work and the two INTERVALS Like DATETIME INTERVAL is a family of types with different precisions An INTERVAL can represent a count of years and months or it can represent a count of days hours minutes seconds or fractions of seconds 18 possible precisions in all The size of an INTERVAL value ranges from 2 to 12 bytes depending on the formulas shown in Figure 9 4 Precision Size Precision Size year p to
489. one Query Result 2 1 119 Bob Shorter The Triathletes Club 2405 Kings Highway Cherry Hill NJ 08002 609 663 6079 122 Cathy O Brian The Sporting Life 543 Nassau Street Princeton NJ 08540 609 342 0054 In relational terminology projection is defined as taking a vertical subset from the columns of a single table that retains the unique rows This kind of SELECT statement returns some of the columns and all of the rows in a table Projection is implemented through the select list in the SELECT clause of a SELECT statement as shown in Query 2 2 SELECT UNIQUE city state zipcode FROM customer Query 2 2 2 6 Composing Simple SELECT Statements Introducing the SELECT Statement Query Result 2 2 contains the same number of rows as the customer table but it projects only a subset of the table s columns city state zipcode Bartlesville OK 74006 Blue Island NY 60406 Brighton MA 02135 Cherry Hill NJ 08002 Denver CO 80219 Jacksonville FL 32256 Los Altos CA 94022 Menlo Park CA 94025 Mountain View CA 94040 Mountain View CA 94063 Oakland CA 94609 Palo Alto CA 94303 Palo Alto CA 94304 Phoenix AZ 85008 Phoenix AZ 85016 Princeton NJ 08540 Redwood City CA 94026 Redwood City CA 94062 Redwood City CA 94063 San Francisco CA 94117 Sunnyvale CA 94085 Sunnyvale CA 94086 Wilmington DE 19898 Query Result 2 2 The most common kind of SELECT statement uses both selection and projection A query o
490. one within a transaction can be rolled back at the end of it To do this reliably the database server normally applies the following rules e All cursors are closed by ending a transaction e All locks are released by ending a transaction These rules are normal with all database systems that support transactions and for most applications they do not cause any trouble However circum stances exist where using standard transactions with cursors are not possible For example a situation is sketched in Figure 7 1 which works fine without transactions However when transactions are added closing the cursor conflicts with using two cursors simultaneously DECLARE master CURSOR FOR DECLARE detail CURSOR FOR FOR UPDATE OPEN master LOOP FETCH master INTO IF the fetched data is appropriate THEN BEGIN WORK OPEN detail USING data read from master FETCH detail UPDATE WHERE CURRENT OF detail COMMIT WORK END IF END LOOP CLOSE MASTER A pseudocode sketch of one common form of database application In this design one cursor is used to scan a table Selected records are used as the basis for updating a different table The problem is that when each update is treated as a separate transaction as shown in the pseudocode in Figure 7 1 the COMMIT WORK statement following the UPDATE closes all cursors including the master cursor The simplest alternative is to move the COMMIT WORK and BEGIN WORK
491. only the c customer_num column is used in the join and output only the index is read no row is read from the table 3 For each row of orders that has a matching customer_num a search is made in the items table using the index on order_num Optimizing Your Queries 13 13 Time Costs of a Query It is not always obvious why the optimizer makes its choices By comparing the plans produced by several variations in the query you can usually deduce some of its logic Time Costs of a Query To execute a query the database server spends most of its time in performing two types of operation reading data from disk and comparing column val ues Of the two reading data is by far the slower task This section examines where the database server spends time The next section explores the implications of making queries faster Activities in Memory The database server can process only data in memory It must read a row into memory before it can test it with a filter expression It must read rows from both tables before it can test a join condition The database server prepares an output row in memory by assembling the selected columns from other rows in memory Most of these activities execute very quickly Depending on the computer the database server can perform hundreds or even thousands of comparisons each second As a result the time spent on in memory work is usually a small part of the whole execution time Two in memory activi
492. onment Simple Concurrency the one the program receives if it sets its lock mode to not wait for locks Thus if your program receives an error code related to locks even after it sets lock mode to wait you know the cause is an impending deadlock Handling External Deadlock A deadlock can also occur between programs on different database servers In this case INFORMIX OnLine Dynamic Server cannot instantly detect the deadlock Perfect deadlock detection requires excessive communications traffic among all database servers in a network Instead each database server sets an upper limit on the amount of time that a program can wait to obtain a lock on data at a different database server If the time expires the database server assumes that a deadlock was the cause and returns a lock related error code In other words when external databases are involved every program runs with a maximum lock waiting time The maximum is set for the database server and can be changed by the database administrator Simple Concurrency If you are not sure which choice to make concerning locking and concurrency and if your application is straightforward have your program execute the following commands when it starts up immediately after the first DATABASE statement n ET LOCK MODE TO WAIT ET ISOLATION TO REPEATABLE READ n Ignore the return codes from both statements Proceed as if no other programs exist If no performance pro
493. ons it is clear that index maintenance is the most time consuming part of data modification One way to reduce this cost is discussed under Dropping Indexes on page 10 24 Choosing Indexes Indexes are required on columns that must be unique and are not specified as primary keys In addition you should add an index in the following cases Columns used in joins that are not specified as foreign keys Columns frequently used in filter expressions Columns frequently used for ordering or grouping Join Columns As discussed in Chapter 13 Optimizing Your Queries at least one column named in any join expression should have an index If no index exists the database server may build a temporary index or perform a sort merge before the join and discard it afterward that is almost always faster than performing a join by repeated sequential scans over a table When both columns in a join expression have indexes the optimizer has more options when it constructs the query plan As a general rule you should put an index on any column that is not identified as a primary or foreign key and is used in a join expression more than occasionally Tuning Your Data Model 10 21 Managing Indexes Selective Filter Columns in Large Tables If a column is often used to filter the rows of a large table consider placing an index on it The optimizer can use the index to select the desired columns avoiding a sequential scan of the e
494. onstants no expressions and no host variables just literal numbers and strings of characters No matter how many times such an INSERT operation occurs the rows it produces are identical In that case there is no point in copying buffering and transmitting each identical row Modifying Data Through SQL Programs 6 11 Using INSERT Instead for this kind of INSERT operation the PUT statement does nothing except to increment a counter When a FLUSH operation is finally performed a single copy of the row and the count of inserts is passed to the database server The database server creates and inserts that many rows in one opera tion It is not common to insert a quantity of identical rows You can do it when you first establish a database to populate a large table with null data An Insert Example Deleting with a Cursor on page 6 7 contains an example of the DELETE statement whose purpose is to look for and delete duplicate rows of a table A better way to do the same thing is to select the desired rows instead of deleting the undesired ones The code in Figure 6 5 shows one way to do this The example is written in INFORMIX 4GL to take advantage of some features that make SQL programming easy 6 12 Modifying Data Through SQL Programs Figure 6 5 Using INSERT BEGIN WORK INSERT INTO new_orders SELECT FROM ORDERS main WHERE 1 SELECT COUNT FROM ORDERS minor WHERE main order_num minor order_num
495. or declared in the preceding example to read once through the items table Cur sors can be declared to read both backward and forward see Cursor Input Modes on page 5 23 This cursor because it lacks a FOR UPDATE clause probably is used only to read data not to modify it The use of cursors to modify data is covered in Chapter 6 Modifying Data Through SQL Programs Opening a Cursor The program opens the cursor when it is ready to use it The OPEN statement activates the cursor It passes the associated SELECT statement to the database server which begins the search for matching rows The database server pro cesses the query to the point of locating or constructing the first row of out put It does not actually return that row of data but it does set a return code in SQLSTATE for SQL APIs and SQLCODE for INFORMIX 4GL and SQL APIs The following example shows the OPEN statement in INFORMIX 4GL OPEN the_item 5 20 Programming with SQL Retrieving Multiple Rows Because this is the first time that the database server has seen the query it is the time when many errors are detected After opening the cursor the program should test SOLSTATE or SQLCODE If the SOLSTATE value is greater than 02000 or the SQLCODE contains a negative number the cursor is not usable There may be an error in the SELECT statement or some other problem may be preventing the database server from executing the statement If SQLSTATE i
496. or applications is reduced You can write a stored procedure to be run with the DBA privilege by a user who does not have the DBA privilege This allows you to limit and control access to data in the database Alternatively a stored procedure can monitor which users access certain tables or data See Controlling Access to Data Using Stored Procedures on page 11 15 for a discussion of this topic Relationship Between SQL and a Stored Procedure You can call a procedure within data manipulation SQL statements and issue SQL statements within a procedure See Chapter 1 of the Informix Guide to SQL Syntax for a complete list of data manipulation SQL statements You use a stored procedure within a data manipulation SQL statement to supply values to that statement For example you can use a procedure to perform the following actions e Supply values to be inserted into a table e Supply a value that makes up part of a condition clause in a SELECT DELETE or UPDATE statement These are two possible uses of a procedure within a data manipulation statement but others exist In fact any expression within a data manipulation SQL statement can consist of a procedure call You can also issue SQL statements within a stored procedure to hide those SQL statements from a database user Rather than having all users learn how to use SQL one experienced SQL user can write a stored procedure to encapsulate an SQL activity and let others know tha
497. or segmenting queries should be dramatically faster The drawback of splitting a table is that operations that apply to the whole table become much more complicated If a query cannot be directed to one subtable it must be written in the form of a UNION of many subqueries each on a different subtable This greatly complicates the design of reports and browsing programs Redundant and Derived Data The data model produced by the methods of Chapter 8 Building Your Data Model contains no redundant data Every attribute appears in only one table The data model also contains no derived data that is data that can be computed from existing attributes is selected as an expression based on those attributes These features minimize the amount of disk space used and make updating the tables as easy as possible However they can force you to use joins and aggregate functions often and that may take more time than is acceptable As an alternative you can introduce new columns that contain redundant or derived data provided you understand the risks Adding Derived Data In the stores6 database no column occurs in the orders table for the total price of an order The reason is that the information can be derived from the rows of the items table A program that wants to report the date and total price of order number 1009 can obtain it with the following query SELECT order_date SUM total_price FROM orders items WHERE orders or
498. ordance with the ANSI standard for SQL Setting the Lock Mode The lock mode determines what happens when your program encounters locked data One of the following things occurs when a program attempts to fetch or modify a locked row e The program receives an immediate return from the database server with an error code in SQLCODE e The program is suspended until the lock is removed by the program that placed it e The program is suspended for a time and then if the lock is not removed it receives an error return code from the database server You choose among these results with the command SET LOCK MODE Waiting for Locks If you prefer to wait and this is the best choice for many applications execute the following command SET LOCK MODE TO WAIT When this lock mode is set your program usually ignores the existence of other concurrent programs When it needs to access a row that another pro gram has locked your program waits until the lock is removed then proceeds The delays are usually imperceptible Programming for a Multiuser Environment 7 13 Setting the Lock Mode Not Waiting for Locks The disadvantage of waiting for locks is that the wait might become very long although properly designed applications should hold their locks very briefly When the possibility of a long delay is not acceptable a program can execute the following command SET LOCK MODE TO NOT WAIT When the program requests a
499. orption mens womens cat_advert lead_time Great durability Specify size Pronators and Supinators Take Heart A Serious Training Shoe For Runners Who Need Motion Control 4 Query Result 2 78 Note that you cannot ORDER BY the TEXT column cat_descr or the BYTE column cat_picture Composing Simple SELECT Statements 2 81 Multiple Table SELECT Statements 2 82 You also can use aliases to shorten your queries on external tables residing in external databases Query 2 79 joins columns from two tables that reside in different databases and systems neither of which is the current database or system SELECT order_num lname fname phone FROM masterdb central customer c sales western orders o WHERE c customer_num o customer_num AND order_num lt 1010 Query 2 79 By assigning the aliases c and o to the long database system table names masterdb central customer and sales western orders respectively you can use the aliases to shorten the expression in the WHERE clause and retrieve the data shown in Query Result 2 79 order_num lname fname phone 1001 Higgins Anthony 415 368 1100 L002 Pauli Ludwig 408 789 8075 1003 Higgins Anthony 415 368 1100 L004 Watson George 415 389 8789 1005 Parmelee Jean 415 534 8822 1006 Lawson Margaret 415 887 7235 1007 Sipes Arnold 415 245 4578 L008 Jaeger Roy 415 743 3611 L009 Keyes Frances 408 277 7245 1010 Grant Alfred 415 356 1123 Query Result 2 79 For more inform
500. otal rows processed It is not used in INFORMIX ESQL Ada fifth Following a syntax error in a PREPARE EXECUTE IMMEDIATE DECLARE or static SQL statement this field contains the offset in the statement text where the error was detected sixth Following a successful fetch of a selected row or a successful insert update or delete i operation this field contains the rowid physical address of the last row processed charactor MEOLA Eiaa Internal use only Figure 5 4 The uses of SQLCODE SQLERRD and SQLERRP Programming with SQL 5 9 Calling the Database Server array of 8 characters SQLAWARN When Opening or Connecting to a Database first Set to W when any field is set to W If this field is blank the others need not be checked second Set to W when the database now open uses a transaction log third Set to W when the database now open is ANSI compliant fourth Set to W when the database server is INFORMIX OnLine Dynamic Server fifth Set to W when the database server stores the FLOAT data type in DECIMAL form done when the host system lacks support for FLOAT types sixth Not used seventh Set to W when the application is connected to an INFORMIX OnLine Dynamic Server database server which is a secondary server in a data replication pair that is the database server is available only for read operations eighth Not used All Other Operations first Set to W when any other field is set to W
501. otherwise fit The space saved by key compression varies with the content of the keys from page to page and index to index To estimate the size of a compact index disregarding space saved by key compression let the values be as shown in the following list keysize the total width of the indexed column or columns petuniq the number of unique entries you expect in this index divided by estrows For a unique index or one with only occasional duplicate values use 1 0 When duplicates are present in significant numbers let pctuniq be a fraction less than 1 0 entsize keysize 5 pctuniq pagents floor pageuse entsize Approximately pagents entries occur on each index page leaves ceiling estrows pagents Approximately leaves leaf pages occur in the index branches ceiling leaves pagents There are approximately branches nonleaf pages The index contains approximately leaves branches pages when it is compact Estimates for two indexes in the customer table are carried out in Figure 10 8 on page 10 17 10 16 Tuning Your Data Model Figure 10 8 Calculating Table Sizes As rows are deleted and new ones inserted the index can become sparse that is the leaf pages might no longer be full of entries On the other hand if key compression is effective the index might be smaller The method given here should yield a conservative estimate for most indexes If index space is important build a large test index usi
502. ou create a view the database server tests to make sure that you have all the privileges needed to execute the SELECT statement in the view definition If you do not the view is not created This test ensures that users cannot gain unauthorized access to a table by creating a view on the table and querying the view After you create the view the database server grants you the creator and owner of the view at least the Select privilege on it No automatic grant is made to public as is the case with a newly created table Granting and Limiting Access to Your Database 11 27 Privileges and Views The database server tests the view definition to see if the view is modifiable If it is the database server grants you the Insert Delete and Update privi leges on the view provided that you also have those privileges on the under lying table or view In other words if the new view is modifiable the database server copies your Insert Delete and Update privileges from the underlying table or view and grants them on the new view If you have only the Insert privilege on the underlying table you receive only the Insert privilege on the view This test ensures that users cannot use a view to gain access to any privileges that they did not already have Because you cannot alter or index a view the Alter and Index privileges are never granted on a view Privileges When Using a View Figure 11 9 When you attempt to use a view the d
503. ou use to associate an indicator variable differs with the language you are using but the principle is the same in all However indica tor variables are not used explicitly in INFORMIX 4GL or in SPL because in those languages null values are supported for variables In 4GL the preceding example is written as follows SELECT paid_date INTO op_date FROM orders WHERE order_num the_order IF op_date IS NULL THEN LET op_date date 01 01 1900 END IF Dealing with Errors Although the database server handles conversion between data types automatically several things still can go wrong with a SELECT statement In SQL programming as in any kind of programming you must anticipate errors and provide for them at every point 5 16 Programming with SQL Retrieving Single Rows End of Data One common event is that no rows satisfy a query This is signalled by an SQLSTATE code of 02000 and by a code of 100 in SQLCODE sqlca sqlcode as it is known in ESQL C following a SELECT statement This code indicates an error or anormal event depending entirely on your application If you are sure that there ought to be a row or rows for example if you are reading a row using a key value that you just read from a row of another table then the end of data code represents a serious failure in the logic of the program On the other hand if you select a row based on a key supplied by a user or some other source that is less reli
504. our Data Model Implementing Your Data Model 9 3 Defining the Domains Data Types The first constraint on any column is the one that is implicit in the data type for the column When you choose a data type you constrain the column so that it contains only values that can be represented by that type Each data type represents certain kinds of information and not others The correct data type for a column is the one that represents all the data values that are proper for that column but as few as possible of the values that are not proper for it Choosing a Data Type Every column ina table must have a data type chosen from the types that the database server supports The choice of data type is important for the following reasons e Itestablishes the basic domain of the column that is the set of valid data items that the column can store e It determines the kinds of operations you can perform on the data For example you cannot apply aggregate functions such as SUM to columns with a character data type e It determines how much space each data item occupies on disk This is not important for small tables but if a table has tens or hundreds of thou sands of rows the difference between a 4 byte and an 8 byte type can be crucial Using Data Types in Referential Constraints Almost all data type combinations must match For example if a primary key is defined as CHAR the foreign key must also be defined as CHAR Howe
505. our database e Names for databases can be up to 18 characters long for INFORMIX OnLine Dynamic Server databases and up to 10 characters long for INFORMIX SE databases The first character of a name must be a letter or an underscore _ Introduction 7 The Demonstration Database You can use letters characters and underscores _ for the rest of the name DB Access makes no distinction between uppercase and lowercase letters The database name should be unique When you run dbaccessdemo6 you are as the creator of the database the owner and Database Administrator DBA of that database If you installed your Informix database server according to the installation instructions the files that make up the demonstration database are protected so you cannot make any changes to the original database You can run the dbaccessdemo6 script again whenever you want to work with a fresh demonstration database The script prompts you when the cre ation of the database is complete and asks if you would like to copy the sam ple command files to the current directory Enter N if you have made changes to the sample files and do not want them replaced with the original versions Enter Y if you want to copy over the sample command files Creating the Demonstration Database Use the following steps to create and populate the demonstration database 1 Set the INFORMIXDIR environment variable so that it contains th
506. p values bigquery exec sql prepare bigq from bigquery exec sql execute bigq using delta acct_number delta teller_number delta branch_number exec sql commit work Preparing and executing a multistatement operation in ESQL C The USING clause of the EXECUTE statement supplies a list of host variables whose values are to take the place of the question marks in the prepared statement Programming with SQL 5 31 Dynamic SQL Using Prepared SELECT Statements A dynamically prepared SELECT statement cannot simply be executed it might produce more than one row of data and the database server not knowing which row to return produces an error code Instead a dynamic SELECT statement is attached to a cursor Then the cursor is opened and used in the usual way The cursor to be used with a prepared statement is declared for that statement name The following example is in INFORMIX 4GL LET select_2 select order_num order_date from orders where customer_num and order_date gt PREPARE q_orders FROM select_2 DECLARE cu_orders CURSOR FOR q_orders OPEN cu_orders USING q_c_number q_o_date FETCH cu_orders INTO f_o_num f_o_date The following list identifies the stages of processing in this example 1 A character string expressing a SELECT statement is placed in a program variable It employs two place holding question marks 2 The PREPARE statement converts the string into a dat
507. p of stores6 A 6R system catalog tables 2 33R mission critical 1 10T naming conventions 1 4225 Index 11 naming unique to engine 9 21T naming with variable 1 423S NLS 1 16T NLS versus non NLS 1 20R NLS accessing 1 20R opening in exclusive mode 1 1425 optimizing queries 1 394S populating new tables 9 27T relation to dbspace 10 5T relational defined 1 11T remote 1 4225 restoring 1 308S server 1 8T 1 16T server definition of 1 16T stopping logging on 1 376S stores6 Intro 9R Intro 12S 7T stores6 description of A 1R table names 12 16T See also Database Name segment Database Administrator DBA 1 233S 11 7T Database application See Application Database lock 7 6T Database management system 12 4T Database Name segment database outside DBPATH 1 423S for remote database 1 422S naming conventions 1 421S naming with variable 1 4235 syntax 1 421S using quotes slashes 1 423S Database server choosing OnLine or SE 1 3R configuration 12 15T definition of 1 16T effect of server type on available data types 1 4R isolation level 1 6R locking 1 5R rolling back transactions 1 4R SQL statements supported 1 7R system catalog tables 1 7R transaction logging 1 5R local 12 5T NLS versus non NLS 1 20R remote 12 8T specifying default for connection 4 36R DATABASE statement determining database type 1 140S exclusive mode 1 142S 7 6T for database outside DBPATH 1 141S locking 7 6T specifying current database 1 140S SQLAWARN af
508. plemented in the logic of client applications by explicitly specifying where data should be found or updated However this way of achieving data replication is costly error prone and difficult to maintain Instead the concept of data replication is often coupled with replication transparency Replication transparency is func tionality built into a database server instead of client applications to automatically handle the details of locating and maintaining data replicas Summary INFORMIX OnLine Dynamic Server Data Replication Summary Within the broad framework of data replication OnLine implements nearly transparent data replication of entire database servers All the data managed by one OnLine database server is replicated and dynamically updated on another OnLine database server usually at a remote site OnLine data repli cation is sometimes called hot site backup because it provides a means of maintaining a backup copy of the entire database server that can be used quickly in the event of a catastrophic failure Because OnLine provides replication transparency you generally do not need to be concerned with or aware of data replication the OnLine adminis trator takes care of it However if your organization decides to use data rep lication you should be aware that special connectivity considerations exist for client applications in a data replication environment These considerations are described in the INFORMIX OnLine
509. plication of a multiple table query in Query 2 76 it is wise to more closely define the SELECT statement by including specific columns in the select list as shown in Query 2 77 SELECT catalog description unit_price unit unit_descr manu_name lead_time FROM catalog stock manufact WHERE catalog stock_num stock stock_num AND stock manu_code manufact manu_code AND catalog_num 10025 Query 2 77 2 78 Composing Simple SELECT Statements Multiple Table SELECT Statements Query 2 77 uses a wildcard to select all columns from the table having the most columns and then specifies columns from the other two tables It pro duces the natural join shown in Query Result 2 77 that displays the same information as the previous example but without duplication catalog_num 10025 stock_num 106 manu_code PRC cat_descr Hard anodized alloy with pearl finish 6mm hex bolt hardware Available in lengths of 90 140mm in 10mm increments cat_picture lt BYTE value gt cat_advert ProCycle Stem with Pearl Finish description bicycle stem unit_price 23 00 unit each unit_descr each manu_name ProCycle lead_time 9 Query Result 2 77 Some Query Shortcuts You can use aliases the INTO TEMP clause and display labels to speed your way through joins and multiple table queries and to produce output for other uses Using Aliases You can make multiple table queries shorter and more readable by assigning aliases to the tables
510. pond affirmatively the current database server tells each one to commit its transactions and then the global transaction is complete If any database server responds negatively or does not respond all database servers are instructed to abort the local transactions A network allows a client application to run in one machine while the database server operates in another computer to which the data is physically attached This provides distributed processing and the possibility of distrib uted database access Many possible combinations exist of network software operating systems and database servers and each has subtleties that must be mastered Understanding Informix Networking 12 21 Summary 12 22 Understanding Informix Networking Section III Using Advanced SQL Optimizing Your Queries Chapter Overview 3 Optimizing Techniques 4 Verifying the Problem 4 Considering the Total System 5 Understanding the Application 5 Measuring the Application 6 Manual Timing 6 Time from Operating System Commands 6 Time from the Programming Language 6 Finding the Guilty Functions 7 Keeping an Open Mind 7 The Query Optimizer 8 How the Optimizer Works 8 How the Optimizer Joins Tables 8 Obtaining Input 9 Assessing Filters 10 Selecting Table Access Paths 11 Selecting the Query Plan 11 Reading the Plan 12 Time Costs ofa Query 14 Activities in Memory 14 Disk Access Management 14 Page Buffers 16 The Cost of Reading a Row 16 The
511. portion of disk space separate from the database In INFORMIX OnLine Dynamic Server this space is called the logical log because the log records represent logical units of the transactions In INFORMIX SE the space used to store log records is called the transaction log file Databases do not generate transaction records automatically The database administrator or the INFORMIX OnLine Dynamic Server administrator for OnLine databases decides whether to make a database use transaction logging Without transaction logging you cannot roll back transactions Logging and Cascading Deletes Logging must be turned on in your database for cascading deletes to work This is because when you specify a cascading delete the delete is first per formed on the primary key of the parent table If the system crashes after the rows of the primary key of the parent table are performed but before the rows of the foreign key of the child table are deleted referential integrity is vio lated If logging is turned off even temporarily deletes do not cascade After logging is turned back on however deletes can cascade again Turn logging on with the CREATE DATABASE statement for INFORMIX OnLine Dynamic Server database servers Specifying Transactions The boundaries of transactions are specified with SOL statements You can do this in two ways In the most common style you specify the start of a multi statement transaction by executing the BEGIN WORK sta
512. pplica tion and the database server reside on the same computer INFORMIX SE databases use a type of IPC connection called unnamed pipes and INFORMIX OnLine Dynamic Server use an IPC connection technique called shared memory e A database server either INFORMIX OnLine Dynamic Server or INFORMIX SE e Databases Advantages and Disadvantages of Local Multiuser Systems A configuration that allows multiple users gives better access to the data than does a single user system With a local database it is still easy to set up and maintain However like the single user system the data is not available to users on other computers and the size of the databases or the amount of processing needed may outgrow the capacity of the computer IPC shared memory provides very fast communication between the client application and the database server However IPC shared memory commu nication is vulnerable to programming errors if the client application does explicit memory addressing or overindexes data arrays Such errors do not affect the application if you use IPC unnamed pipes or network communication See Single Machine Configuration Using Network Communication on page 12 9 Understanding Informix Networking 12 7 Database Management System Configurations A Remote Configuration Figure 12 3 shows a remote configuration where the application resides on one computer and the database server and its associated databases reside on anothe
513. pressions 21 Assigning Values to Variables 21 Program Flow Control 22 Branching 22 Looping 23 Function Handling 24 Calling Procedures Within a Procedure 24 Running an Operating System Command from Within a Procedure 24 Recursively Calling a Procedure 24 Passing Information into and out of a Procedure 25 Returning Results 25 Specifying Return Data Types 25 Returning the Value 26 Returning More Than One Set of Values froma Procedure 26 Exception Handling 27 Trapping an Error and Recovering 28 Scope of Control of an ON EXCEPTION Statement 29 User Generated Exceptions 30 Simulating SQL Errors 31 Using RAISE EXCEPTION to Exit Nested Code 32 Summary 33 14 2 Creating and Using Stored Procedures Chapter Overview You can write procedures using SQL and some additional statements belong ing to the Stored Procedure Language SPL and store this procedure in the database These stored procedures are effective tools for controlling SOL activity This chapter provides instruction on how to write stored procedures To help you learn how to write them examples of working stored procedures are provided The syntax for each of the SPL statements is described in Chapter 2 of the Informix Guide to SQL Syntax Accompanying the syntax for each statement are usage notes and examples pertinent to that statement Introduction to Stored Procedures and SPL To SQL a stored procedure is a user defined function Anyone who has the Resource pr
514. program assembles the text of an SQL statement as a character string which is stored in a program variable 2 It executes a PREPARE statement which asks the database server to examine the statement text and prepare it for execution 3 It uses the EXECUTE statement to execute the prepared statement In this way a program can construct and then use any SQL statement based on user input of any kind For example it can read a file of SQL statements and prepare and execute each DB Access the utility that you use to explore SQL interactively is an INFORMIX ESQL C program that constructs prepares and executes SQL statements dynamically For example it enables users to specify the columns of a table using simple interactive menus When the user is finished DB Access builds the necessary CREATE TABLE or ALTER TABLE statement dynamically and prepares and executes it Preparing a Statement In form a dynamic SQL statement is like any other SQL statement that is written into a program except that it cannot contain the names of any host variables This leads to two restrictions First if it is a SELECT statement it cannot include the INTO clause The INTO clause names host variables into which column data is placed and host variables are not allowed in a dynamic state ment Second wherever the name of a host variable normally appears in an expression a question mark is written as a placeholder You can prepare a statement in thi
515. ps that the optimizer takes to evaluate queries These sections are meant to give you a basic idea of what the opti mizer does so that you can understand how to streamline your queries as described in later sections How the Optimizer Joins Tables The optimizer in Informix database servers does an exhaustive search on all joined tables regardless of whether the joins contain filters or indexes and removes redundant pairs as it builds the paths Consider the following example SELECT FROM customer c items i orders o WHERE c customer_num o customer_num AND o order_num i order_num The optimizer forms all possible join pairs between the tables and then removes redundant join pairs It keeps the least expensive join triples as shown in the following example c 1 c o i c 1 0 0 0 1 13 8 Optimizing Your Queries The Query Optimizer Obtaining Input The optimizer can be successful only if its estimates are accurate They need not be accurate in absolute terms but they must be relatively accurate so that better plans produce lower estimates than worse plans However the opti mizer has only limited information To make its work take a small fraction of the execution time it has to make do with the information in the system cat alog tables and other summary information No time exists for example for the optimizer to perform a SELECT COUNT operation to obtain an accurate count of the rows in
516. query plan being used The following list contains some things to look for Indexes Examine the output to see if indexes are used and if so how they are used Filters Examine your filters to make sure that they are selective enough Query Examine your query again to make sure that the access plan is optimal Examining the Indexes You should study the indexes or the lack of indexes on the columns of your query Consider using some of the methods that are described in the following sections to improve your query Replacing Autoindexes with Indexes If the query plan includes an autoindex path to a large table take it as a recommendation from the optimizer that an index should be on that column It is reasonable to let the database server build and discard an index if you perform the query only occasionally but if the query is done even daily you save time by creating a permanent index Creating Data Distributions on Filtered Columns Executing the UPDATE STATISTICS statement in MEDIUM or HIGH mode causes information about the distribution of data values for each column specified to be placed in a system catalog table called sysdistrib This infor mation is used at optimization time to estimate the number of rows that match a given query and from that to estimate the cost of retrieving those values From these cost estimates the optimizer determines the best path of execution Data distributions supercede the colmin and colmax colum
517. r Data Model Defining the Domains Altering the Next SERIAL Number The starting value for a SERIAL column is set when the column is created see Using CREATE TABLE on page 9 24 You can use the ALTER TABLE statement later to reset the next value the value that is used for the next inserted row You cannot set the next value below the current maximum value in the column because that can lead the database server to generate duplicate numbers However you can set the next value to any value higher than the current maximum thus creating gaps in the sequence Approximate Numbers FLOAT and SMALLFLOAT In scientific engineering and statistical applications numbers are often known to only a few digits of accuracy and the magnitude of a number is as important as its exact digits The floating point data types are designed for these applications They can represent any numerical quantity fractional or whole over a wide range of magnitudes from the cosmic to the microscopic For example they can easily represent both the average distance from the Earth to the Sun 1 5 x 10 meters or Planck s constant 6 625 x 10 Their only restriction is their lim ited precision Floating point numbers retain only the most significant digits of their value If a value has no more digits than a floating point number can store the value is stored exactly If it has more digits it is stored in approximate form with its least significant
518. r NVARCHAR m r data type is used the rows of a table have varying lengths instead of fixed lengths This has mixed effects on the speed of database operations Because more rows fit in a disk page the database server can search the table using fewer disk operations than if the rows were of fixed length As a result queries can execute more quickly Insert and delete operations can be a little quicker for the same reason When you update a row the amount of work the database server must do depends on the length of the new row as compared with the old one If the new row is the same size or shorter execution time is not significantly dif ferent than it is with fixed length rows But if the new row is longer than the old one the database server might have to perform several times as many disk operations Thus updates of a table that uses VARCHAR m r or NVAR CHAR m r data can sometimes be slower than updates of a fixed length field You can mitigate this effect by specifying r as a size that covers a high proportion of the data items Then most rows use the reserve length only a little space is wasted in padding and updates are only slow when a normal value is replaced with one of the rare longer ones Large Character Objects TEXT The TEXT data type stores a block of text It is designed to store self contained documents business forms program source or data files or memos Although you can store any data in a TEXT item Infor
519. r an update cursor The locks are placed individually as each row is examined They are not released until the cursor closes or a transaction ends Repeatable Read allows a program that uses a scroll cursor to read selected rows more than once and to be sure that they are not modified or deleted between readings Scroll cursors are described in Chapter 5 Programming with SQL No lower isolation level guarantees that rows still exist and are unchanged the second time they are read Repeatable Read isolation places the largest number of locks and holds them the longest Therefore it is the level that reduces concurrency the most If your program uses this level of isolation you must think carefully about how many locks it places how long they are held and what the effect can be on other programs In addition to the effect on concurrency the large number of locks can be a problem The database server records only a fixed number of locks for all the programs it serves This number is adjustable If that table fills up the 7 12 Programming for a Multiuser Environment Setting the Lock Mode database server cannot place a lock and returns an error code The person who administers an INFORMIX OnLine Dynamic Server system can monitor the lock table and tell you when it is heavily used Repeatable Read is automatically the isolation level in an ANSI compliant database Repeatable Read is required to ensure operations behave in acc
520. r computer on the network In contrast the database servers in Figure 12 1 and Figure 12 2 are local database servers host 1 host 2 application t somnecti h gt aS database eee _ Sere networ application connection databases Figure 12 3 A simple network connection In Figure 12 3 the applications might be INFORMIX ESQL COBOL or INFORMIX ESQL C applications The database server might be INFORMIX OnLine Dynamic Server UNIX or INFORMIX OnLine for Net Ware PC Different computers are referred to as sites or host machines The database server in Figure 12 3 is a remote database server because it is on a different host machine or site from the application that uses its services A database server can be local with respect to one application and remote with respect to another application as illustrated in Figure 12 6 on page 12 13 Advantages and Disadvantages of Remote Network Connections The configuration shown in Figure 12 3 isan example of distributed processing In distributed processing multiple computers contribute to a single comput ing task In this example host 1 handles the computing requirements of the application such as screen display generation of reports and printing and 12 8 Understanding Informix Networking Database Management System Configurations host2 handles the computing required to manipulate information in the databases Using a network also gives the client applicat
521. r many errors that count is zero because they prevented the database server from beginning the operation at all For example if the named table does not exist or if a column tested in the WHERE clause is renamed no deletions are attempted However certain errors can be discovered after the operation begins and some rows are processed The most common of these errors is a lock conflict The database server must obtain an exclusive lock on a row before it can delete that row Other programs might be using the rows from the table pre venting the database server from locking a row Because the issue of locking affects all types of modifications it is discussed Chapter 7 Programming for a Multiuser Environment Other rarer types of error can strike after deletions begin for example hardware errors that occur while the database is being updated 6 4 Modifying Data Through SQL Programs Using DELETE Using Transaction Logging The best way to prepare for any kind of error during a modification is to use transaction logging In the event of an error of any kind you can tell the data base server to put the database back the way it was The following example is based on the preceding INFORMIX ESQL C example which is extended to use transactions exec sql begin work start the transaction exec sql delete from items where order_num onum del_result sqlca sqlcode save two error del_isamno sqlca sqlerrd
522. r to a fraction of a second The INTERVAL data type stores a span of time that is a duration Calendar Dates DATE The DATE data type stores a calendar date A DATE value is actually a signed integer whose contents are interpreted as a count of full days since midnight on December 31 1899 Most often it holds a positive count of days into the current century The DATE format has ample precision to carry dates into the far future 58 000 centuries Negative DATE values are interpreted as counts of days prior to the epoch date that is a DATE of 1 represents the day December 30 1899 Because DATE values are integers Informix database servers permit them to be used in arithmetic expressions For example you can take the average of a DATE column or you can add 7 or 365 to a DATE column In addition a rich set of functions exist specifically for manipulating DATE values See Chapter 1 of the Informix Guide to SQL Syntax The DATE data type is compact at 4 bytes per item Arithmetic functions and comparisons execute quickly on a DATE column Exact Points in Time DATETIME The DATETIME data type stores any moment in time in the era beginning 1 A D In fact DATETIME is really a family of 28 data types each with a dif ferent precision When you define a DATETIME column you specify its preci sion It may contain any sequence from the list year month day hour minute second and fraction Thus you can define a DATETIME column
523. ration is the special relationship between the database and the transaction log file An archive copy is an image of the database at one instant The log file contains the history of modifications that were made during that instant It is important that those two instants are identical in other words it is important to start a new transaction log file immediately upon making an archive copy of the database Then if you must restore the database from the archive tape the transaction log contains exactly the history needed to bring it forward in time from that instant to the latest update The statement that applies a log to a restored database is ROLLFORWARD DATABASE You start a new log file by using whatever operating system com mands are needed to delete the file and re create it empty or simply to set the length of the file to zero A transaction log file can grow to extreme size If you update a row ten times just one row exists in the database but ten update events are recorded in the log file If the size of the log file is a problem you can start a fresh log Choose a time when the database is not being updated so no transactions are active and copy the existing log to another medium That copy represents all mod ifications for some period of time preserve it carefully Then start a new log file If you ever have to restore the database you must apply all the log files in their correct sequence Archiving with INFORMIX OnLine D
524. rchives and back up logical logs you also may be able to create your own backup copies using ON Archive See your INFORMIX OnLine Dynamic Server Archive and Backup Guide for more information Concurrency and Locks If your database is contained in a single user workstation without a network connecting it to other machines concurrency is unimportant In all other cases you must allow for the possibility that while your program is modify ing data another program is also reading or modifying the same data This is concurrency two or more independent uses of the same data at the same time A high level of concurrency is crucial to good performance in a multiuser database system Unless controls exist on the use of data however concur rency can lead to a variety of negative effects Programs could read obsolete data modifications could be lost even though it seems they were entered successfully Modifying Data 4 27 Data Replication The database server prevents errors of this kind by imposing a system of locks A lock is a claim or reservation that a program can place on a piece of data The database server guarantees that as long as the data is locked no other program can modify it When another program requests the data the database server either makes the program wait or turns it back with an error You use two statements to control the effect that locks have on your data access SET LOCK MODE and SET ISOLATION You can un
525. re you assume the privileges of a DBA for the duration of the procedure A DBA privileged procedure acts as if the user running the procedure is first granted DBA privilege then executes each statement of the procedure manually and finally has DBA privilege revoked Objects created in the course of running a DBA procedure are owned by the user running the procedure unless the data definition statement in the procedure explicitly names the owner to be someone else Creating and Using Stored Procedures 14 15 Variables and Expressions Privileges and Nested Procedures DBA privileged status is not inherited by a called procedure For example if a DBA privileged procedure executes an owner privileged procedure the owner privileged procedure does not run as a DBA procedure If an owner privileged procedure calls a DBA privileged procedure the statements within the DBA privileged procedure execute as they would within any DBA privileged procedure Revoking Privileges The owner of a procedure can revoke Execute privilege from a user If a user loses the Execute privilege on a procedure the Execute privilege also is revoked from all users who were granted the Execute privilege by that user Variables and Expressions This section discusses how to define and use variables in SPL The differences between SPL and SQL expressions also are covered here Variables You can use a variable in a stored procedure in several ways You can u
526. re that is shown in the following example The procedure uses the SPL to calculate the change that needs to be made to the total_price column when quantity is updated in the items table The procedure receives both the old and new values of quantity and the old value of total_price It divides the old total price by the old quantity to derive the unit price It then multiplies the unit price by the new quantity to obtain the new total price CREATE PROCEDURE calc_totpr old_qty SMALLINT new_qty SMALLINT total MONEY 8 RETURNING MONEY 8 DEFINE u_price LIKE items total_price DEFINE n_total LIKE items total_price LET u_price total old_qty LET n_total new_qty u_price RETURN n_total END PROCEDURE In this example SPL enables the trigger to derive data that is not directly available from the triggering table Creating and Using Triggers 15 11 Tracing Triggered Actions Updating Nontriggering Columns with Data from a Stored Procedure Within a triggered action the INTO clause of the EXECUTE PROCEDURE statement lets you update nontriggering columns in the triggering table The EXECUTE PROCEDURE statement in the following example calls the calc_ totpr stored procedure that contains an INTO clause which references the column total_price FOR EACH ROW EXECUTE PROCEDURE calc_totpr pre_upd quantity post_upd quantity pre_upd total_price INTO total_price The value that is updat
527. re unique an index on the columns 4 b and c in that order can be used in the following ways e To evaluate filter expressions on column a e To join column a to another table Toimplement ORDER BY or GROUP BY on columns a ab or abc but not on b c ac or bc When you create a composite index place the columns in the index in the order from most frequently used to least frequently used If your application is performing several long queries each of which involves a sort on the same columns you might save time by creating a composite index on those columns In effect you perform the sort once and save its output for use in every query Using oncheck on Suspect Indexes With some database servers it is possible for an index to become ineffective because it has been internally corrupted If a query that uses an index has slowed down inexplicably use the oncheck utility to check the integrity of the index and to repair it if necessary The secheck utility does the same job for INFORMIX SE Dropping and Rebuilding Indexes After Updates After extensive amounts of updating after the replacement of a fourth or more of the rows of a table the structure of an index can become inefficient If an index seems to be less effective than it should be yet oncheck reports no errors try dropping the index and re creating it Refining the Column Filters The most efficient queries access only a small body of information You contro
528. rent columns or apply different criteria to rows depending on what the user wants This can be done with dynamic SQL in which the program composes an SQL statement as a string of characters in memory and passes it to the database server to be executed Dynamic statements are not part of the program source text they are constructed in memory during execution Program Variables and Host Variables Figure 5 2 Application programs can use program variables within SQL statements In INFORMIX 4GL and SPL you put the program variable in the SQL statement as syntax allows For example a DELETE statement can use a pro gram variable in its WHERE clause Figure 5 2 shows a program variable in INFORMIX 4GL MAIN UO EFINE drop_number INT ET drop_number 108 ELETE FROM items WHERE order_num drop_number i iw Using a program variable in INFORMIX 4GL Programming with SQL 5 5 SQL in Programs Figure 5 3 Figure 5 3 shows a program variable in SPL CREATE PROCEDURE delete_item drop_number INT DELETE FROM items WHERE order_num drop_number Using a program variable in SPL In applications that use embedded SQL statements the SQL statements can refer to the contents of program variables A program variable that is named in an embedded SQL statement is called a host variable because the SQL statement is thought of as being a guest in the program The following example is a DELETE state
529. resents the contents of one table row After you have the data in a file you can load it into a table using the dbload utility Read about dbload in Chapter 5 of the Informix Guide to SQL Reference The LOAD statement in DB Access INFORMIX SQL or INFORMIX 4GL can also load rows from a flat ASCII file See Chapter 1 of the Informix Guide to SQL Syntax for information about the LOAD and UNLOAD statements Inserting hundreds or thousands of rows goes much faster if you turn off transaction logging No point exists in logging these insertions because in the event of a failure you can easily re create the lost work The following list contains the steps of a large bulk load operation e Ifany chance exists that other users are using the database exclude them with the DATABASE EXCLUSIVE statement e If you are using INFORMIX OnLine Dynamic Server ask the administrator to turn off logging for the database The existing logs can be used to recover the database to its present state while the bulk insertion can be run again to recover those rows if they are lost soon after 9 28 Implementing Your Data Model Summary Summary Perform the statements or run the utilities that load the tables with data Archive the newly loaded database If you are using INFORMIX OnLine Dynamic Server either ask the administrator to perform a full or incremental archive or use the onunload utility to make a binary copy of your database only If you
530. riable is left unchanged it contains the default value initially set At this point in the program the programmer sees no need to trap such errors and report them 5 18 Programming with SQL Retrieving Multiple Rows The following example is an expansion of an earlier INFORMIX 4GL example that displays default values if it cannot find the company that the user requests DEFINE cfname clname ccompany CHAR 20 DEFINE cnumbr INTEGER P ROMPT Enter the customer number FOR cnumbr LET cfname unknown LET clname person LET ccompany noplace SELECT fname lname company INTO cfname clname ccompany WHERE customer_num cnumbr DISPLAY cfname clname at ccompany This query does not use aggregates so if no row matches the user specified customer number SQLCODE is set to 100 and the host variables remain unchanged Retrieving Multiple Rows When any chance exists that a query could return more than one row the program must execute the query differently Multirow queries are handled in two stages First the program starts the query No data is returned immediately Then the program requests the rows of data one at a time These operations are performed using a special data object called a cursor A cursor is a data structure that represents the current state of a query The following list is the general sequence of program operations 1 The program declares the cursor and its as
531. rial value inserted into a table o The number of rows processed by SELECT INSERT DELETE UPDATE and EXECUTE PROCEDURE statements New Environment Variables The following Informix environment variables and X Open categories described in Chapter 4 of the Informix Guide to SQL Reference are new in Version 6 0 o ARC DEFAULT o ARC_KEYPAD o COLLCHAR o DBAPICODE o DBNLS o DBSPACETEMP o DBUPSPACE o ENVIGNORE o INFORMIXC Introduction 11 New Features in Informix Version 6 0 Products That Use SQL 12 Introduction o INFORMIXSERVER o INFORMIXSHMBASE o INFORMIXSTACKSIZE o LANG o LC COLLATE o LC_CTYPE o LC_MONETARY o LC_NUMERIC o LC_TIME New Data Distribution Features You can use the UPDATE STATISTICS statement to create data distributions for each table The database server uses these data distribu tions to improve the choice of execution paths for SELECT statements The new data distribution feature affects application development in the following three ways o The syntax for the UPDATE STATISTICS statement has been expanded o Anew environment variable DBUPSPACE sets the upper limit of disk space that you want to use when columns are sorted o You can use the dbschema utility to print distribution information Introduction of Environment Configuration Files The following environment configuration files can contain default values of environment variables o INFORMIXDIR etc informix rc o info
532. rigger text in a program 15 16T 15 17T Errors after DELETE 6 4T at compile time 14 6T codes for 5 11T dealing with 5 16T detected on opening cursor 5 20T during updates 4 22T in stored procedure syntax 14 7T inserting with a cursor 6 11T ISAM error code 5 12T using to identify NLS database server 1 19R ESCAPE keyword syntax in Condition segment 1 405S use in Condition segment 1 409S with LIKE keyword 1 328S 1 4115 with MATCHES keyword 1 329S 1 4125 with WHERE keyword 1 3285 2 43T ESQL cursor use 5 19T to 5 28T DELETE statement in 6 3T delimiting host variables 5 6T dynamic embedding 5 5T 5 28T error handling 5 16T fetching rows from cursor 5 21T host variable 5 6T 5 8T indicator variable 5 15T INSERT in 6 8T NLS errors in SQLERRM field 1 19R overview 5 3T to 5 37T 6 3T to 6 17T preprocessor 5 4T scroll cursor 5 23T selecting single rows 5 13T SQL Communications Area 5 8T SQLCODE 5 11T SQLERRD fields 5 12T static embedding 5 5T UPDATE in 6 14T Estimating blobpages 10 17T maximum number of extents 10 10T size of index 10 16T table size with fixed length rows 10 13T table size with variable length rows 10 14T Example database See Demonstration database EXCLUSIVE keyword syntax in DATABASE 1 140S in LOCK TABLE 1 260S use in DATABASE 1 1425 in LOCK TABLE 1 262S Exclusive lock 7 6T EXECUTE IMMEDIATE statement description of 5 34T restricted statement types 1 1915 syntax and usage 1 190S using with concatena
533. ring inventory A company makes a variety of parts for example Some parts are discrete but some are assemblages of other parts These relationships are documented in a single table which might be called contains The column contains parent holds the part numbers of parts that are assemblages The column contains child has the part number of a part that is acomponent of the parent If part 123400 is an assembly of nine parts nine rows exist with 123400 in the first column and other part numbers in the second 5 26 Programming with SQL Figure 5 6 Retrieving Multiple Rows CONTAINS PARENT CHILD FKNN FK NN 123400 432100 432100 765899 The parts explosion problem is this given a part number produce a list of all parts that are components of that part A sketch of one solution as implemented in INFORMIX 4GL is shown in Figure 5 6 DEFINE part_list ARRAY 200 OF INTEGER FUNCTION boom top_part DEFINE this_part child_part INTEGI DEFINE next_to_do next_free SMALL DECLARE part_scan CURSOR FOR SELECT child INTO child_part F WHERE parent this_part ER INT ROM contains LET next_to_do 1 LET part_list next_to_do top_part LET next_free 2 WHILE next_to_do lt next_free this_part part_list next_to_do FOREACH part_scan LET part_list next_free child_part LET next_free next_free 1 END FOREACH LET next_to_do next_to_do 1 END WHILE RETU
534. ripting The following section contains examples that illustrate these types of queries Including Rows Use the relational operator to include rows in a WHERE clause as shown in Query 2 21 SELECT customer_num call_code call_dtime res_dtime FROM cust_calls WHERE user_id maryj Query 2 21 Query 2 21 returns the set of rows shown in Query Result 2 21 customer_num call_code call_dtime res_dtime 106 D 1993 06 12 08 20 1993 06 12 08 25 121 0 1993 07 10 14 05 1993 07 10 14 06 E240 1 1993 07 31 14 30 Query Result 2 21 Excluding Rows Use the relational operators or lt gt to exclude rows in a WHERE clause Query 2 22 assumes that you are selecting from an ANSI compliant database the statements specify the owner or login name of the creator of the customer table This qualifier is not required when the creator of the table is the current 2 30 Composing Simple SELECT Statements Single Table SELECT Statements user or when the database is not ANSI compliant although it is not incorrect to include it in either case For a complete discussion of owner naming see Chapter 1 in the Informix Guide to SQL Syntax SELECT customer_num company state FROM odin customer WHERE state CA city SELECT customer_num company state FROM odin customer WHERE state lt gt CA City Query 2 22 Both statements in Query 2 22 exclude values by specifying that in the customer table ow
535. rmix These optional files allow the administrator or the user to set environment variables in much the same way a login or profile file is used so that the variables do not need to be set at each session Section I Using Basic SQL Chapter Introducing Database Features and SOL Chapter Overview 3 Databases What and Why 3 The Data Model 3 Storing Data 6 Querying Data 6 Modifying Data 8 Concurrent Use and Security 8 Centralized Management 9 Group and Private Databases 10 Essential Databases 10 Important Database Terms 11 The Relational Model 11 Tables 11 Columns 12 Rows 12 Tables Rows and Columns 12 Operations on Tables 13 Structured Query Language 14 Standard SQL 14 Informix SQL and ANSISQL 15 ANSI Compliant Databases 15 NLS Databases 16 The Database Software 16 The Applications 16 The Database Server 16 Interactive SQL 17 Reports and Forms 17 General Programming 17 Applications and Database Servers 18 Summary 18 1 2 Introducing Database Features and SQL Chapter Overview This is a book about databases and about how you can exploit them using Informix software Your real use of a database begins with the SELECT state ment which is described in Chapter 2 Composing Simple SELECT State ments If you are in a hurry and if you know at least a little about databases turn to it now This chapter covers the fundamental concepts of databases and defines some terms that are use
536. ro baseball 126 00 132 3000 3 Husky baseball bat 240 00 252 0000 4 Hero football 480 00 504 0000 4 Husky football 960 00 1008 0000 306 Shimara tandem adapter 190 00 199 5000 307 ProCycle infant jogger 250 00 262 5000 308 ProCycle twin jogger 280 00 294 0000 309 Hero ear drops 40 00 42 0000 309 Shimara ear drops 40 00 42 0000 310 Anza kick board 84 00 88 2000 310 Shimara kick board 80 00 84 0000 311 Shimara water gloves 48 00 50 4000 312 Hero racer goggles 72 00 75 6000 312 Shimara racer goggles 96 00 100 8000 313 Anza swim cap 60 00 63 0000 313 Shimara swim cap 72 00 75 6000 Query Result 2 80 You can query on this table and join it with other tables which avoids a mul tiple sort and lets you move more quickly through the database Temporary tables are discussed at greater length in Chapter 13 Optimizing Your Que ries Composing Simple SELECT Statements 2 83 Summary Summary This chapter introduced sample syntax and results for basic kinds of SELECT statements that are used to query on a relational database Earlier sections of the chapter showed how to perform the following activities Select all columns and rows from a table with the SELECT and FROM clauses Select specific columns from a table with the SELECT and FROM clauses Select specific rows from a table with the SELECT FROM and WHERE clauses Use the DISTINCT or UNIQUE keyword in the SELECT clause to eliminate dupl
537. ro names No you decide no point exists for recording a number unless it is used by someone You write 1 under number voice and opposite name name address number voice name none 0 n 1 0 1 0 n Fill out the rest of the matrix in the same fashion using the following decisions e Aname can be associated with more than one fax number for example a company can have several fax machines Going the other way a fax num ber can be associated with more than one name for example several people can use the same fax number e A modem number must be associated with exactly one name This is an arbitrary decree to complicate the example pretend it is a requirement of the design However a name can have more than one associated modem number for example a company computer can have several dial up lines e Although some relationship exists between a voice number and an address a modem number and an address and a fax number and an Building Your Data Model 8 13 Identifying and Defining Your Principal Data Objects address in the real world none needs to be recorded in this model There already is an indirect relationship through name name address number number number voice fax modem name none 0 n 1 1 n 1 0 1 0 n 0 n 0 n address none none none none number none none none voice number none none fax number none modem Figure 8 5 A complet
538. roductive time by the database users as well as the loss of business and good will while users cannot work A plan for regular archiving of critical databases can help avoid or mitigate these potential disasters A large database used by many people must be maintained and tuned Someone must monitor its use of system resources chart its growth antici pate bottlenecks and plan for expansion Users will report problems in the application programs someone must diagnose these and correct them If rapid response is important someone must study and analyze the performance of the system and find the causes of slow responses Introducing Database Features and SQL 1 9 Databases What and Why Group and Private Databases Some Informix database servers are designed to manage relatively small databases that are used privately by individuals or that are shared among a small group of users These database servers for example INFORMIX SE for the UNIX operating system store databases in files managed by the host operating system These databases can be archived using the same procedures for backing up files that work with other computer files that is copying the files to another medium when they are not in use The only difference is that when a database is archived its transaction log file must be reset to empty The use of transaction logs is discussed in Chapter 7 Programming for a Multiuser Environment Chapter 10 Tuning Your D
539. rogram Commenting and Documenting a Procedure Observe that the read_address procedure in Figure 14 1 includes comments and a DOCUMENT clause The comments are incorporated into the text of the procedure Any characters following a double hyphen are considered to be a comment The double hyphen can be used anywhere within a line The text in the DOCUMENT clause should give a summary of the procedure You can extract this text by querying the sysprocbody system catalog table See Looking at the Procedure Documentation on page 14 9 for more information about reading the DOCUMENT clause Diagnosing Compile Time Errors When you issue a CREATE PROCEDURE or CREATE PROCEDURE FROM statement the statement fails if a syntax error occurs in the body of the procedure The database server stops processing the text of the procedure and returns the location of the error Finding Syntax Errors in a Procedure Using DB Access If a procedure created using DB Access has a syntax error when you choose the Modify option of the SQL menu the cursor sits on the line containing the offending syntax 14 6 Creating and Using Stored Procedures Creating and Using Stored Procedures Finding Syntax Errors in a Procedure Using an SQL API Figure 14 3 If a procedure created using an SQL API has a syntax error the CREATE PROCEDURE statement fails The database server sets the SOQLCODE field of the SQLCA to a negative number and sets the fifth elem
540. rom fewer than SMALLFLOAT up to twice the precision of FLOAT The magnitude of a DECIMAL p number ranges from 10 19 to 10174 It is easy to be confused about decimal data types The one under discussion is DECIMAL p that is DECIMAL with only a precision specified The size of DECIMAL p numbers depends on their precision they occupy 1 p 2 bytes rounded up to a whole number if necessary DECIMAL p has the following advantages over FLOAT e Precision can be set to suit the application from highly approximate to highly precise e Numbers with as many as 32 digits can be represented exactly e Storage is used in proportion to the precision of the number e Every Informix database server supports the same precision and range of magnitudes regardless of the host operating system The DECIMAL p data type has the following disadvantages e Arithmetic and sorting are somewhat slower than on FLOAT numbers e Many programming languages do not support the DECIMAL p data format the way they support FLOAT and INTEGER When a program extracts a DECIMAL p value from the database it may have to convert the value to another format for processing However INFORMIX 4GL programs can use DECIMAL p values directly Fixed Point Numbers DECIMAL and MONEY Most commercial applications need to store numbers that have fixed numbers of digits on the right and left of the decimal point Amounts of money are the most common examples Amounts in
541. rop it explicitly using the DROP PROCEDURE statement before you can create another procedure with the same name If you debug your procedure and attempt to use the CREATE PROCEDURE statement with the same procedure name again the attempt fails unless you first drop the existing procedure from the database Privileges on Stored Procedures A stored procedure resides in the database in which it was created As with other database objects you need appropriate privileges to create a stored pro cedure In addition you need appropriate privileges to execute a stored procedure Two types of stored procedures exist in a database DBA privileged and owner privileged When you create the procedure you specify which type it is You need different privileges to create and execute these two types of pro cedures The differences are described in the sections that follow and are summarized in Figure 14 8 Creating and Using Stored Procedures 14 13 Privileges on Stored Procedures Can be created by Users having Execute privilege by default Privileges the procedure owner or DBA must grant another user to enable that user to run a procedure DBA privileged procedure Any user with the DBA privilege Any user with the DBA privilege Execute privilege Owner privileged procedure Any user with at least the Resource privilege Not ANSI compliant Public any user with Connect database privilege ANSI compliant The pr
542. ror See Disk mirroring MOD function syntax in expression 1 444S use in expression 1 446S MODE ANSI keywords ANSI compliant database 1 15T ANSI compliant logging 9 23T specifying ANSI compliance 1 11R specifying transactions 4 24T syntax in CREATE DATABASE 1 57S in START DATABASE 1 376S use in CREATE DATABASE 1 60S in START DATABASE 1 377S Model See Data model MODIFY keyword syntax in ALTER TABLE 1 15S use in ALTER TABLE 1 278 MODIFY NEXT SIZE keywords syntax in ALTER TABLE 1 15S use in ALTER TABLE 1 335 MONEY data type 9 12T changing data types 3 23R description of 3 16R 9 10T display format 9 12T in INSERT 4 8T syntax 1 425S using as default value 1 195 1 89S See also DECIMAL data type MONEY value setting DBMONEY environment variable 4 20R setting LC_MONETARY environment variable 4 52R specifying European format with DBMONEY 4 20R specifying for NLS 4 53R Money representing with NLS 1 15R MONTH function as time function 2 56T syntax in expression 1 454S use in expression 1 456S MONTH keyword syntax in DATETIME data type 1 4285 in INTERVAL data type 1 485S use as DATETIME field qualifier 3 8R 1 488S as INTERVAL field qualifier 3 13R 1 491S Multiple triggers column numbers in 1 115S example 1 1145 order of execution 1 115S preventing overriding 1 132S Multiple table join 2 77T Multi row query destination of returned values 1 198S managing with FETCH 1 195S N Naming convention column 1 875 1 102S
543. rror messages on the screen finderr or print formatted error messages rofferr See the Introduction to the Informix Error Messages manual for a detailed description of these scripts The optional Informix Messages and Corrections product provides PostScript files that contain the error messages and their corrective actions If you have installed this product you can print the PostScript files on a Post Script printer The PostScript error messages are distributed in a number of files of the format errmsg1 ps errmsg2 ps and so on These files are located in the INFORMIXDIR msg directory The Demonstration Database The DB Access utility which is provided with your Informix database server products includes a demonstration database called stores6 that contains information about a fictitious wholesale sporting goods distributor The sam ple command files that make up a demonstration application are also included Most of the examples in this manual are based on the stores6 demonstration database The stores6 database is described in detail and its contents are listed in Appendix A of the Informix Guide to SQL Reference The script that you use to install the demonstration database is called dbaccessdemo6 and is located in the INFORMIXDIR bin directory The data base name that you supply is the name given to the demonstration database If you do not supply a database name the name defaults to stores6 Follow these rules for naming y
544. rs that journal is read and all updates are applied in a batch Programming for a Multiuser Environment 7 7 How Locks Work Page Row and Key Locks One row of a table is the smallest object that can be locked A program can lock one row or a selection of rows while other programs continue to work on other rows of the same table INFORMIX OnLine Dynamic Server stores data in units called disk pages Its disk storage methods are described in detail in Chapter 10 Tuning Your Data Model A disk page contains one or more rows In some cases it is better to lock a disk page than to lock individual rows on it You choose between locking by rows or locking by pages when you create the table INFORMIX OnLine Dynamic Server supports a clause LOCK MODE to specify either page or row locking You can specify lock mode in the CREATE TABLE statement and later change it with the ALTER TABLE statement Other Informix database servers do not offer the choice they lock by row or by page whichever makes the better implementation Page and row locking are used identically Whenever INFORMIX OnLine Dynamic Server needs to lock a row it locks either the row itself or the page it is on depending on the lock mode established for the table In certain cases the database server has to lock a row that does not exist in effect it locks the place in the table where the row would be if it did exist The database server does this by placing a
545. ry 2 61 the EXTEND function restricts the two DATETIME values by displaying only the specified subfields SELECT customer_num EXTEND call_dtime month to minute call_time EXTEND res_dtime month to minute res_time FROM cust_calls ORDER BY res_time Query 2 61 Query Result 2 61 returns the month to minute range for the columns labeled call_time and res_time and gives an indication of the workload customer_num call_time res_time 127 2O7 32 T4230 106 06 12 08 20 06 12 08 25 119 07 01 15 00 07 02 08 21 110 07 07 10 24 07 07 10 30 121 07 10 14 05 07 10 14 06 116 11 28 13 34 11 28 16 47 116 12 21 11 24 12 27 08 19 Query Result 2 61 Composing Simple SELECT Statements 2 61 Single Table SELECT Statements Using the DATE Function Query 2 62 retrieves DATETIME values only when call_dtime is later than the specified DATE SELECT customer_num call_dtime res_dtime FROM cust_calls WHERE call_dtime gt DATE 12 31 92 Query 2 62 Query Result 2 62 returns the following rows customer_num call_dtime res_dtime 106 08 25 110 119 121 127 1993 06 12 08 20 1993 07 07 10 24 1993 07 01 15 00 1993 07 10 14 05 19 9 3204 234 14 53 0 1993 06 12 1993 07 07 10 30 1993 07 02 08 21 1993 07 10 14 06 Query Result 2 62 Query 2 63 converts DATETIME values to DATE format and displays the values with labels only when call_dtime is greater than or equal to the specified date SEL
546. s This assignment statement concatenates the following six character strings GRANT e The parameter specifying the privileges to be granted e ON e The parameter specifying the table name TO The parameter specifying the user The result is a complete GRANT statement composed partly of program input The same feat can be accomplished in other host languages using different syntax as shown in the following figure WHENEVER ERROR CONTINUE PREPARE the_grant FROM grant_stmt If the database server returns an error code in SQLCODE the default action of an INFORMIX 4GL program is to terminate However errors are quite likely when you prepare an SQL statement composed of user supplied parts and program termination is a poor way to diagnose the error In the preceding code the WHENEVER statement prevents termination Then the PREPARE statement passes the assembled statement text to the database server for parsing 5 36 Programming with SQL Summary Summary If the database server approves the form of the statement it sets a zero return code This does not guarantee that the statement is executed properly it means only that the statement has correct syntax It might refer to a nonexist ent table or contain many other kinds of errors that can only be detected during execution IF status 0 THEN EXECUTE the_grant END IF If the preparation is successful the next step is to execute the prepared
547. s 6 ASCII and PostScript Error Message Files 7 The Demonstration Database 7 Creating the Demonstration Database 8 New Features in Informix Version 6 0 Products That UseSQL 9 Introducing Database Features and SQL Chapter Overview 1 3 Databases What and Why 1 3 The Data Model 1 3 Concurrent Use and Security 1 8 Centralized Management 1 9 Important Database Terms 1 11 The Relational Model 1 11 Structured Query Language 1 14 Standard SQL 1 14 Informix SQL and ANSI SQL 1 15 ANSI Compliant Databases 1 15 NLS Databases 1 16 The Database Software 1 16 The Applications 1 16 The Database Server 1 16 Interactive SQL 1 17 Chapter 2 Chapter 3 viii Table of Contents Reports and Forms 1 17 General Programming 1 17 Applications and Database Servers 1 18 Summary 1 18 Composing Simple SELECT Statements Chapter Overview 2 3 Introducing the SELECT Statement 2 4 Some Basic Concepts 2 4 The Forms of SELECT 2 10 Special Data Types 2 11 Single Table SELECT Statements 2 11 Selecting All Columns and Rows 2 12 Selecting SpecificColumns 2 18 Using the WHERE Clause 2 28 Creating a Comparison Condition 2 29 Expressions and Derived Values 2 46 Using Functions in SELECT Statements 2 53 Using Stored Procedures in SELECT Statements 2 67 Multiple Table SELECT Statements 2 69 Creating a Cartesian Product 2 69 Creating aJoin 2 71 Some Query Shortcuts 2 79 Summary 2 84 Composing Advanced SELECT Statements Chapter Overview 3 3 U
548. s and Disadvantages of Local Multiuser Systems 7 A Remote Configuration 8 Advantages and Disadvantages of Remote Network Connections 8 Single Machine Configuration Using Network Communication 9 Advantages and Disadvantages of Local Loopback 10 Distributed Databases 10 Advantages and Disadvantages of Distributed Databases 11 Distributed Databases Using Multiple Vendor Servers 11 Connecting to Data on a UNIX Network 12 Example of Client Server Connections 13 Environment Variables 14 Connection Information 15 SQL Connection Statements 16 Accessing Tables 16 Using Synonyms with Table Names 17 Synonym Chains 18 Protecting Your Data in a Networked Environment 19 Data Protection with INFORMIX SE 19 Data Protection with INFORMIX OnLine Dynamic Server 19 Data Replication 19 Archives 20 Data Integrity for Distributed Data 20 Two Phase Commit 20 Summary 21 12 2 Understanding Informix Networking Chapter Overview This chapter gives an overview of the use of databases on a computer network It introduces some commonly used terminology and illustrates var ious network configurations The chapter also presents an overview of how the components of either a local or network connection fit together so that a client application can find data on a database server We will discuss the following networking configurations that you can use with Informix databases and point out some of their effects on performance and usability e Allon o
549. s and can simplify the work of the optimizer in other ways Using a Temporary Table to Avoid Multiple Sorts For example suppose your application produces a series of reports on customers who have outstanding balances one report for each major postal area ordered by customer name In other words a series of queries occur each of the following form using hypothetical table and column names SELECT cust name rcvbles balance other columns FROM cust rcvbles WHERE cust customer_id rcvbles customer_id AND rcevbls balance gt 0 AND cust postcode LIKE 98_ ORDER BY cust name This query reads the entire cust table For every row with the right postcode the database server searches the index on revbles customer_id and performs a nonsequential disk access for every match The rows are written to a temporary file and sorted This procedure is acceptable if the query is done only once but this example includes a series of queries each incurring the same amount of work 13 36 Optimizing Your Queries Making Queries Faster An alternative is to select all customers with outstanding balances into a temporary table ordered by customer name as shown in the following example SELECT cust name rcvbles balance other columns FROM cust rcvbles WHERE cust customer_id rcvbles customer_id AND cvbls balance gt 0 ORDER BY cust name INTO TEMP cust_with_balance Now you can direct queries against th
550. s are relatively simple when compared with the more advanced SELECT statements use them carefully because they change the contents of the database Modifying Data 4 3 Statements That Modify Data Deleting Rows The DELETE statement removes any row or combination of rows from a table You cannot recover a deleted row after the transaction is committed Trans actions are discussed under Interrupted Modifications on page 4 22 For now think of a transaction and a statement as the same thing When deleting a row you must also be careful to delete any rows of other tables whose values depend on the deleted row If however your database enforces referential constraints you can use the ON DELETE CASCADE option of the CREATE TABLE or ALTER TABLE statements to allow deletes to cascade from one table in a relationship to another For more information on referen tial constraints and the ON DELETE CASCADE option refer to the section Referential Integrity on page 4 19 Deleting All Rows of a Table The DELETE statement specifies a table and usually contains a WHERE clause that designates the row or rows that are to be removed from the table If the WHERE clause is left out all rows are deleted Do not execute the following statement DELETE FROM customer Because this DELETE statement does not contain a WHERE clause all rows from the customer table are deleted If you attempt an unconditional delete using the DB A
551. s equal to 00000 or SOLCODE contains a zero the SELECT statement is syntactically valid and the cursor is ready for use At this point however the program does not know if the cursor can produce any rows Fetching Rows The program uses the FETCH statement to retrieve each row of output This statement names a cursor and also can name the host variables to receive the data Here is the INFORMIX 4GL example completed DECLARE the_item CURSOR FOR SELECT order_num item_num stock_num INTO o_num i_num s_num FROM items OPEN the_item WHILE sqlcode 0 FETCH the_item IF sqlcode 0 THEN DISPLAY o_num i_num s_num END IF END WHILE Detecting End of Data In the previous example the WHILE condition prevents execution of the loop in case the OPEN statement returns an error The same condition terminates the loop when SQLCODE is set to 100 to signal the end of data However the loop contains a test of SQLCODE This test is necessary because if the SELECT Programming with SQL 5 21 Retrieving Multiple Rows statement is valid yet finds no matching rows the OPEN statement returns a zero but the first fetch returns 100 end of data and no data The following example shows another way to write the same loop DECLARE the_item CURSOR FOR SELECT order_num item_num stock_num INTO o_num i_num s_num FROM items OPEN the_item IF sqlcode 0 THEN FETCH the_item fetch first row END IF WHILE sqlcode
552. s form for execution with the PREPARE statement The following example is in INFORMIX ESOLI C exec sql prepare query_2 from select from orders where customer_num and order_date gt Notice the two question marks in this example they indicate that when the statement is executed the values of host variables are used at those two points Programming with SQL 5 29 Dynamic SQL You can prepare almost any SQL statement dynamically The only ones that cannot be prepared are the ones directly concerned with dynamic SQL and cursor management such as the PREPARE and OPEN statements After you prepare an UPDATE or DELETE statement it is a good idea to test the fifth field of SQLAWARN to see if you used a WHERE clause see The SOLAWARN Array on page 5 12 The result of preparing a statement is a data structure that represents the statement This data structure is not the same as the string of characters that produced it In the PREPARE statement you give a name to the data structure it is query_2 in the preceding example This name is used to execute the prepared SQL statement The PREPARE statement does not limit the character string to one statement It may contain multiple SQL statements separated by semicolons Figure 5 7 shows a fairly complex example in INFORMIX ESQL COBOL MOVE BEGIN WORK PDATE account SET balance balance WHERE acct_number UPDATE teller SET balance balance WHERE te
553. s from the two queries removes duplicates and returns what is left Because the results of the queries are combined into a single result the select list in each query must have the same number of columns Also the corresponding columns selected from each table must be of the same data type CHARACTER type columns must be the same length and these corresponding columns must either all allow or all disallow nulls Composing Advanced SELECT Statements 3 43 Set Operations Query 3 36 performs a union on the stock_num and manu_code columns in the stock and items tables SELECT DISTINCT stock_num manu_code FROM stock WHERE unit_price lt 25 00 UNION SELECT stock_num manu_code FROM items WHERE quantity gt 3 Query 3 36 Query 3 36 selects those items that have a unit price of less than 25 00 or that have been ordered in quantities greater than three and lists their stock_num and manu_code as shown in Query Result 3 36 stock_num manu_code ANZ NRG SMT 9 ANZ 103 PRC 106 PRC 201 NKL 301 KAR 302 HRO 302 KAR or ol on Query Result 3 36 3 44 Composing Advanced SELECT Statements Set Operations If you include an ORDER BY clause it must follow Query 3 36 and use an integer not an identifier to refer to the ordering column Ordering takes place after the set operation is complete SELECT DISTINCT stock_num manu_code FROM stock WHERE unit_price lt 25 00 UNION n Gl E Gl
554. s it to your program To display the text of the message follow the procedure that your Informix application development tool provides for retrieving the text of an SQL error message Generating a Variable Error Message Error number 746 allows you to provide the text of the error message As with the preceding example the following one also generates an error if new_qty is greater than old_qty multiplied by 1 50 However in this case the error number is 746 and the message text Too many items for Mfr is supplied as the third argument in the RAISE EXCEPTION statement See the RAISE EXCEPTION statement in Chapter 14 Creating and Using Stored Pro cedures for more information on the syntax and use of this statement CREATE PROCEDURE upd_items_p2 EFINE GLOBAL old_qty INT DEFAULT 0 EFINE new_qty INT ET new_qty SELECT SUM quantity FROM items F new_qty gt old_qty 1 50 THEN RAISE EXCEPTION 746 0 Too many items for Mfr END IF END PROCEDURE aeoy 15 16 Creating and Using Triggers Summary Figure 15 5 Summary If you use DB Access to submit the triggering statement and if new_qty is greater than old_qty the result of this stored procedure is as shown in Figure 15 5 soL New Run Modify Use editor Output Choose Save Info Drop Exit Modify the current SQL statements using the SQL editor store6 myserver Press CTRL W for Help INSERT INTO items VALUES 2 1001 2 HRO
555. se e Index Often Sometimes Rarely Never e Table of Contents Often Sometimes Rarely Never e Quick Reference Card Often Sometimes Rarely Never e Chapter summaries O Often J Sometimes Rarely J Never e On line help Often Sometimes Rarely Never Browse through manuals Often Sometimes Rarely Never 5 How long have you been developing database applications e How many years have you been programming 0 1 3 14 5 L155 e How many years have you been using databases 0 1 3 14 5 L155 e How many years have you been using Informix products 10 11 3 14 5 1 gt 5 6 Have you used other programming languages If so which ones 7 Have you used other database products If so which ones January 1993 9 What other Informix products do you use 10 What is your job title and area of responsibility 11 Additional comments Your Name Company Name Address City State Province Country Zip Postal Code Telephone Number INFORMIX is a registered trademark of Informix Software Inc To mail this card please fold on the dotted line and staple or tape the open end BUSINESS REPLY MAIL FIRSTCLASS PERMIT NO 25 MENLO PARK CA POSTAGE WILL BE PAID BY ADDRESSEE Vd INFORMIX Informix Software Inc Technical Publications Department 4100 Bohannon Drive Menlo Park California 94025 NO POSTAGE NECESSARY IF M
556. se a variable in a database query or other SQL statement wherever a constant is expected You can use a variable with SPL statements to assign and calculate values keep track of the number of rows returned from a query and execute a loop as well as handle other tasks The value of a variable is held in memory the variable is not a database object Hence rolling back a transaction does not restore values of procedural variables Format of Variables A variable follows the rules of an SQL identifier See Chapter 1 of the Informix Guide to SQL Syntax Once you define a variable you can use it anywhere in the procedure as appropriate If you are using an SQL API you do not have to set off the variable with a special symbol unlike host variables in an SQL API 14 16 Creating and Using Stored Procedures Variables and Expressions Global and Local Variables You can define a variable to be either local or global A variable is local by default The following outline provides the differences between the two types Local A local variable is available only within the procedure in which it is defined Local variables do not allow a default value to be assigned at compile time Global A global variable is available to other procedures run by the same user session in the same database The values of global variables are stored in memory The global environment is the memory used by all the procedures run within a given session on
557. se they are different they make each row unique If no one such column exists the primary key is a composite of two or more columns whose values taken together are different in every row 8 22 Building Your Data Model Translating E R Data Objects Into Relational Constructs Every table in the model must have a primary key This follows automatically from the rule that all rows must be unique If necessary the primary key is composed of all the columns taken together The primary key should be a numeric data type INT or SMALLINT SERIAL data type or a short character string as used for codes It is recommended that you avoid using long character strings as primary keys Null values are never allowed in a primary key column Null values are not comparable that is they cannot be said to be alike or different Hence they cannot make a row unique from other rows If a column permits null values it cannot be part of a primary key What is a Null Value Columns ina table may be designated as containing null values This means that the value for the column may be unknown or not applicable For exam ple in the telephone directory example the anniv column of the name table may contain null values if you do not know the person s anniversary you do not specify it Be careful not to confuse null value with zero or blank value Some entities have ready made primary keys such as catalog codes or identity numbers which are define
558. servers Detailed instructions for setting up local and network connec tions for both Version 6 0 products and earlier products are given in the INFORMIX OnLine Dynamic Server Administrator s Guide and the INFORMIX SE Administrator s Guide Example of Client Server Connections Figure 12 6 Figure 12 6 shows both local and networked connections of Version 6 0 products Although all these connections are possible you cannot do them all at once Client X can make connection 1 2 or 3 and Client Y can make connection 4 or 5 host 1 host 2 4 6 0 6 0 7 OnLine A B OnLine B 6 0 client Y va 5 3 1 6 0 client X Local and network connection of version 6 0 products You can connect clients directly to INFORMIX OnLine Dynamic Server database servers using either shared memory IPC or a network communi cations Notice also that OnLine database servers OnLine A and OnLine B can communicate with each other Understanding Informix Networking 12 13 Connecting to Data on a UNIX Network Local clients can connect directly to an INFORMIX SEdatabase server using unnamed pipes IPC Clients using network communications connect to INFORMIX SE by connecting first to a daemon sqlexecd A daemon is a back ground process that listens for requests from other programs The sqlexecd daemon is started by the system administrator When a client requests a con nection to an INFORMIX SE database server sqlexecd notices the r
559. shown in Figure 6 2 int delDupOrder int ord_num int dup_cnt ret_code exec sql declare scan_ord cursor for select order_num order_date into ord_num ord_date from orders for update exec sql open scan_ord if sqlca sqlcode 0 return sqlca sqlcode exec sql begin work for 7 exec sql fetch next scan_ord if sqlca sqlcode 0 break dup_cnt 0 default in case of error exec sql select count into dup_cnt from orders where order_num ord_num if dup_cnt gt 1 exec sql delete where current of scan_ord if sqlca sqlcode 0 break ret_code sqlca sqlcode if ret_code 100 merely end of data exec sql commit work else error on fetch or on delete exec sql rollback work return ret_code An unsafe ESQL C function that deletes through a cursor see Warning Warning The design of the ESQLIC function in Figure 6 2 is unsafe It depends for correct operation on the current isolation level which is discussed later in the chapter Even when it works as intended its effects depend on the physical order of rows in the table which is not generally a good idea Modifying Data Through SQL Programs 6 7 Using INSERT The purpose of the function is to delete rows containing duplicate order numbers In fact in the demonstration database the orders order_num col umn has a unique index so duplicate rows cannot occur in it However a similar fun
560. sign Optimizing Your Queries 13 3 Optimizing Techniques Optimizing Techniques Before you begin optimizing your SQL statements begin considering them as part of a larger system that includes the following components One or more programs The saved queries compiled screen forms and reports and programs in one or more languages in which SQL statements are embedded One or more stored procedures The compiled procedures comprising SQL and SPL statements which are stored in an executable form in the database One or more computers The machines that store the programs and the databases One or more maintainers The people responsible for maintaining the programs One or more users The people whose work the system is supposed to amplify or simplify One or more organizations The groups that own the computers and choose what work is to be done You may work in a large corporation where each of these components is separate or you may be the proprietor maintainer and sole user of a desktop workstation In every case it is important to recognize two points about the system as a whole First the goal of the system is to serve its users Any effort you spend optimizing programs is wasted unless the result helps the users in some way Second SQL statements are only a small part of the system Effective improvements can be found in many parts of a system The following paragraphs outline a general procedure for analyz
561. sing the GROUP BY and HAVING Clauses 3 4 Using the GROUP BY Clause 3 4 Using the HAVING Clause 3 9 Creating Advanced Joins 3 11 Self Joins 3 11 Outer Joins 3 21 Subqueries in SELECT Statements 3 32 Using ALL 3 33 Using ANY 3 34 Single Valued Subqueries 3 36 Correlated Subqueries 3 37 Using EXISTS 3 38 Chapter 4 Chapter 5 Set Operations 3 42 Union 3 43 Intersection 3 51 Difference 3 53 Summary 3 54 Modifying Data Chapter Overview 4 3 Statements That Modify Data 4 3 Deleting Rows 4 4 Deleting a Known Number of Rows 4 4 Inserting Rows 4 6 Updating Rows 4 11 Database Privileges 4 15 Displaying Table Privileges 4 16 Data Integrity 4 17 Entity Integrity 4 18 Semantic Integrity 4 18 Referential Integrity 4 19 Interrupted Modifications 4 22 The Transaction 4 23 Transaction Logging 4 24 Specifying Transactions 4 24 Archives and Logs 4 25 Archiving with INFORMIX SE 4 26 Archiving with INFORMIX OnLine Dynamic Server 4 26 Concurrency and Locks 4 27 Data Replication 4 28 INFORMIX OnLine Dynamic Server Data Replication 4 29 Summary 4 29 Programming with SQL Chapter Overview 5 3 SQL in Programs 5 3 Static Embedding 5 5 Dynamic Statements 5 5 Program Variables and Host Variables 5 5 Calling the Database Server 5 8 The SQL Communications Area 5 8 The SQLCODE Field 5 11 The SQLERRD Array 5 12 The SQLAWARN Array 5 12 The SQLSTATE Value 5 12 Table of Contents ix Chapter 6 Chapter 7 x Table of Contents Retriev
562. single data items are larger than one or two pages each if kept in the dbspace their transfer dilutes the effectiveness of the page buffers When the number of pages of blob data is more than half the number of pages of row data if kept in the dbspace the table is inflated and queries against it are slowed For a table that is both relatively small and nonvolatile you can achieve the effect of a dedicated blobspace by the following means Load the entire table with rows in which the blob columns are null Create all indexes The row pages and the index pages are now contiguous Update all the rows to install the blob data The blob pages follow the pages of row and index data in the tblspace Managing Indexes An index is necessary on any column or composition of columns that must be unique However as discussed in Chapter 13 Optimizing Your Queries the presence of an index can also allow the query optimizer to speed up a query The optimizer can use an index in the following ways e To replace repeated sequential scans of a table with nonsequential access e To avoid reading row data at all when processing expressions that name only indexed columns Tuning Your Data Model 10 19 Managing Indexes e Toavoida sort including building a temporary table when executing the GROUP BY and ORDER BY clauses As a result an index on the right column can save thousands tens of thousands or in extreme cases even millions of
563. sociated SELECT statement This merely allocates storage to hold the cursor 2 The program opens the cursor This starts the execution of the associated SELECT statement and detects any errors in it 3 The program fetches a row of data into host variables and processes it The program closes the cursor after the last row is fetched These operations are performed with SQL statements named DECLARE OPEN FETCH and CLOSE Programming with SQL 5 19 Retrieving Multiple Rows Declaring a Cursor You declare a cursor using the DECLARE statement This statement gives the cursor a name specifies its use and associates it with a statement The following simple example is written in INFORMIX 4GL DECLARE the_item CURSOR FOR SELECT order_num item_num stock_num INTO o_num i_num s_num FROM items The declaration gives the cursor a name the_item in this case and associates it with a SELECT statement Chapter 6 Modifying Data Through SQL Programs discusses how a cursor also can be associated with an INSERT statement The SELECT statement in this example contains an INTO clause That is one of two ways in which you can specify the variables that receive data The other way using the FETCH statement is discussed in Locating the INTO Clause on page 5 22 The DECLARE statement is not an active statement it merely establishes the features of the cursor and allocates storage for it You can use the curs
564. space often is much faster than writing to an operating system file You use the PSORT_DBTEMP environment variable to specify one or more directories where temporary infor mation is stored in operating system files in a round robin manner If PSORT_DBTEMP is not set temporary information is written to the dbspaces specified by the DBSPACETEMP environment variable in a round robin manner If both PPORT_DBTEMP and DBSPACETEMP are not set tem porary information is written to the dbspaces specified by the DBSPACETEMP ONCONFIG param eter in a round robin manner If none of these environment variables or ONCONFIG parameter are set temporary information is written to operating system files in tmp For additional infor mation about environment variables see Chapter 4 of Informix Guide to SQL Reference For additional information about the ONCONFIG file see the INFORMIX OnLine Dynamic Server Administrator s Guide Optimizing Your Queries 13 15 Time Costs of a Query The size of a page depends on the database server With INFORMIX OnLine Dynamic Server the page size is set when OnLine is initialized It is usually 2 kilobytes 2 048 bytes but you can ask the person who installed OnLine to tell you what was chosen Other Informix database servers use the file stor age of the host operating system so their page size is the block size used by the host operating system One kilobyte 1 024 bytes is typical It is possible to define tables so
565. ssociating attributes with entities Normalizing your data model can do the following things e Produce greater flexibility in your design e Ensure that attributes are placed in the proper tables Reduce data redundancy e Increase programmer effectiveness e Lower application maintenance costs e Maximize stability of the data structure Normalization consists of several steps to reduce the entities to more desirable physical properties These steps are called normalization rules also referred to as normal forms Several normal forms exist this chapter discusses the first three normal forms Each normal form constrains the data to be more organized than the last form Because of this you must achieve first normal form before you can achieve second normal form and you must achieve second normal form before you can achieve third normal form First Normal Form An entity is in first normal form if it contains no repeating groups In relational terms this means that a table is in first normal form if it contains no repeating columns Repeating columns make your data less flexible waste Building Your Data Model 8 29 Normalizing Your Data Model Figure 8 14 Figure 8 15 disk space and make it more difficult to search for data In the telephone directory example it appears that the name table contains repeating columns child1 child2 and child3 as shown in Figure 8 14 name rec_num Iname f
566. st 13 32T Literal DATETIME in Condition segment 1 405S in expression 1 436S 1 441S segment 1 487S syntax 1 488S syntax in INSERT 1 250S use in ALTER TABLE 1 188 use in CREATE TABLE 1 885 with IN keyword 1 327S DATE using as a default value 1 19S 1 898 INTERVAL in Condition segment 1 405S in expression 1 436S 1 441S segment 1 490S syntax 1 491S syntax in INSERT 1 250S using as default value 1 195 1 895 Number in Condition segment 1 405S in expression 1 436S 1 439S segment 1 493S syntax 1 493S syntax in INSERT 1 250S with IN keyword 1 409S LOAD statement DELIMITER clause 1 258S input formats for data 1 256S INSERT INTO clause 1 258S loading VARCHAR TEXT or BYTE data types 1 257S specifying field delimiter with DBDELIMITER 4 18R specifying the table to load into 1 2585 syntax 1 255S the LOAD FROM file 1 256S Loading data from a command file into a table 5 20R Local loopback 12 9T Local server 12 5T LOCK MODE keywords syntax in ALTER TABLE 1 155 in CREATE TABLE 1 108S use in ALTER TABLE 1 335 in CREATE TABLE 1 108S LOCK TABLE statement in databases with transactions 1 261S in databases without transactions 1 262S locking a table explicitly 7 7T syntax 1 260S Locking and concurrency 4 27T and integrity 7 3T deadlock 7 14T description of 7 5T during delete 1 159S inserts 1 249S updates 1 152S5 1 385S granularity 7 6T in OnLine 1 5R in SE 1 6R lock duration 7 8T lock mode 7 13T not wait 7 14T wait
567. stem catalog tables 2 11R to 2 33R unlocking 1 381S variable length rows 10 14T See also ALTER TABLE statement See also CREATE TABLE statement See also Join See also Table Name segment TABLE keyword syntax in UPDATE STATISTICS 1 393S Table Name segment 1 506S Table size calculating 10 12T 10 19T cost of access 13 19T 13 34T with fixed length rows 10 13T with variable length rows 10 14T Table level privilege column specific privileges 1 303S 11 10T default with GRANT 1 237S definition and use 1 236S 11 7T granting 1 235S passing grant ability 1 237S revoking 1 301S See also ALTER TABLE statement TABLES keyword in INFO statement 1 2425 tabtype 2 29R 2 30R 1 60S TAN function syntax in expression 1 4585 use in expression 1 460S tblspace description of 10 7T used for BLOB data 10 18T TEMP keyword syntax in SELECT 1 310S use in SELECT 1 3415 TEMP TABLE keywords syntax in CREATE TABLE 1 845 Temporary files specifying directory with DBTEMP 4 27R tables specifying dbspace with DBSPACETEMP 4 26R Temporary table and active set of cursor 5 24T assigning column names 3 12T building distributions 1 397S creating constraints for 1 102S DBSPACETEMP environment variable 1 100S example 4 11T explicit 1 100S implicit 1 100S location of 1 100S naming 1 100S shared disk space for 10 6T updating statistics 1 394S using to speed query 13 36T when deleted 1 100S TERM environment variable 4 55R TERMCAP environm
568. straint FOREIGN KEY keywords in ALTER TABLE 1 295 in CREATE TABLE 1 928 Format for crtcmap mapping file 5 6R specifying for DATE value with DBDATE 4 16R specifying for DATETIME value with DBTIME 4 27R specifying for MONEY value with DBMONEY 4 20R FRACTION keyword syntax in DATETIME data type 1 428S in INTERVAL data type 1 485S use as DATETIME field qualifier 3 8R 1 488S as INTERVAL field qualifier 3 14R 1 4915 FREE statement effect on cursors 1 269S freeing prepared statements 5 33T syntax 1 207S with concatenation operator 1 432S FROM keyword alias names 2 79T syntax in PUT 1 2845 in REVOKE 1 300S in SELECT 1 310S use in PUT 1 287S in SELECT 1 323S Function aggregate 2 53T algebraic 1 444S date oriented 2 56T in SELECT statements 2 53T within a stored procedure 14 24T Function expression DBINFO function 1 4485 description of 1 443S in SELECT 1 3145 Functional dependency 8 31T G GET DESCRIPTOR statement syntax 1 210S the COUNT keyword 1 212S use with FETCH statement 1 200S with concatenation operator 1 432S X Open mode 1 2135 GET DIAGNOSTICS statement CLASS_ORIGIN keyword 1 225S CONNECTION_NAME keyword 1 227S exception clause 1 223S MESSAGE_LENGTH keyword 1 225S MESSAGE_TEXT keyword 1 225S MORE keyword 1 222S NUMBER keyword 1 223S purpose 1 2175 RETURNED_SOLSTATE keyword 1 225S ROW_COUNT keyword 1 2235 SERVER_NAME keyword 1 225S statement clause 1 2225 keywords 1 2225 SUBCLAS
569. sult of sorting the table By placing an index on the ordering column or columns you can replace many sorts during queries with a single sort when the index is created Duplicate Keys Slow Index Modifications When duplicate keys are permitted in an index the entries that have any single value are grouped in a list When the selectivity of the column is high these lists are generally short But when only a few unique values occur the lists become quite long and in fact can cross multiple leaf pages 10 22 Tuning Your Data Model Managing Indexes For example in an index on a column whose only values are M for married and S for single all the index entries are contained in just two lists of dupli cates Such an index is not of much use but at least it works for querying the database server can read out the list of rows that have one value or the other When an entry must be deleted from a list of duplicates the database server must read the whole list and rewrite some part of it When it adds an entry the database server puts the new row at the end of its list Neither operation is a problem when the list is short which is normal But when a list fills many pages the database server must read all the rows to find the end When it deletes an entry it typically must update and rewrite half the pages in the list Thus an index on a column that has a small number of distinct values in a table that has a large number of rows ca
570. t A trigger consists of a trigger event and a triggered action The CREATE TRIGGER statement consists of clauses that perform the following actions e Assign a trigger name e Specify the trigger event that is the table and the type of action that initiate the trigger Define the SQL actions that are triggered An optional clause called the REFERENCING clause is discussed later under Using FOR EACH ROW Triggered Actions on page 15 8 You can create a trigger using the DB Access utility or one of the SQL APIs INFORMIX ESQL C or INFORMIX ESQL COBOL This section describes the CREATE TRIGGER statement as you would enter it using the interactive Query language option in DB Access In an SOL API you simply precede the statement with the symbol or keywords that identify it as an embedded statement 15 4 Creating and Using Triggers How to Create a Trigger Assigning a Trigger Name The trigger name identifies the trigger It follows the words CREATE TRIGGER in the statement It can be up to 18 characters inclusive in length beginning with a letter and consisting of letters the digits 0 9 and the underscore In the following example the portion of the CREATE TRIGGER statement that is shown assigns the name upqty to the trigger CREATE TRIGGER upqty assign trigger name Specifying the Trigger Event The trigger event is the type of statement that activates the trigger When a statement of this type is p
571. t is a row that is not visible through the view It is also possible to update a row of a view so that it no longer satisfies the conditions of the view Granting and Limiting Access to Your Database 11 25 Using Views If this is improper you can add the clause WITH CHECK OPTION when you create the view This clause asks the database server to test every inserted or updated row to ensure that it meets the conditions set by the WHERE clause of the view The database server rejects the operation with an error if the conditions are not met In Figure 11 8 the view named call_response is defined as shown in the following example CREATE VIEW call_response user_id received resolved duration AS SELECT user_id call_dtime res_dtime res_dtime call_dtime FROM cust_calls WHERE user_id USER It is possible to update the user_id column of the view as shown in the following example UPDATE call_response SET user_id lenora WHERE received BETWEEN TODAY AND TODAY 7 The view requires rows in which user_id equals USER If this update is performed by a user named tony the updated rows vanish from the view However you can create the view as shown in the following example CREATE VIEW call_response user_id received resolved duration AS SELECT user_id call_dtime res_dtime res_dtime call_dtime FROM cust_calls WHERE user_id USER WITH CHECK OPTION The preceding update by
572. t least one disk page When blob values are stored in the tblspace the pages of their data are interspersed among the pages containing rows The result is to inflate the size of the table The blobpages separate the pages containing rows and spread them out on the disk When the database server reads only the rows and not the blob data the disk arm must move farther than it would if the blobpages 10 18 Tuning Your Data Model Managing Indexes were stored apart The database server scans only the row pages on any SELECT operation that retrieves no blob column and whenever it tests rows using a filter expression Another consideration is that disk I O to and from a dbspace is buffered Pages are held in storage in case they are needed again soon and when pages are written the requesting program is allowed to continue before the actual disk write takes place However disk I O to and from blobspaces is not buffered Blobspace pages are not retained in buffers to be read again and the requesting program is not allowed to proceed until all output to them is complete The reason is that blobspace I O is expected to be voluminous If these pages are passed through the normal buffering mechanisms they could monopolize the buffers driving out index pages and other pages that are useful to good performance For best performance then you should locate a TEXT or BYTE column ina blobspace in either of the following circumstances When
573. t privilege to the database cannot exercise their Index privilege This is reasonable because an index can fill a large amount of disk space Granting and Limiting Access to Your Database 11 9 Granting Privileges The Alter privilege permits its holder to use the ALTER TABLE statement on the table including the power to add and drop columns reset the starting point for SERIAL columns and so on You should grant the Alter privilege only to users who understand the data model very well and whom you trust to exercise their power very carefully The References privilege allows you to impose referential constraints on a table As with the Alter privilege you should grant the References privilege only to users who understand the data model very well Column Level Privileges You can qualify the Select Update and References privileges with the names of specific columns This allows you to grant very specific access to a table You can permit a user to see only certain columns you can allow a user to update only certain columns or you can allow a user to impose referential constraints on certain columns Using INFORMIX OnLine Dynamic Server so that table data can be inspected only through a call to the database server this feature solves the problem posed earlier that only certain users should know the salary perfor mance review or other sensitive attributes of an employee To make the example specific suppose a table of employee d
574. t process The key to resolving many to many relationships is to separate the two entities and create two one to many relationships between them with a third intersect entity The intersect entity usually contains attributes from both connecting entities 8 26 Building Your Data Model Resolving Your Relationships To resolve a many to many relationship analyze your business rules again Have you accurately diagrammed the relationship In the telephone directory example we have a many to many relationship between the name and fax entities as shown in Figure 8 12 on page 8 26 To resolve the relation ship between name and fax we carefully reviewed the business rules The business rules say One person can have zero one or many fax numbers a fax number can be for several people Based on what we selected earlier as our primary key for the voice entity a many to many relationship exists A problem exists in the fax entity because the telephone number which is designated as the primary key can appear more than one time in the fax entity this violates the qualification of a primary key Remember the primary key must be unique This many to many relationship is resolved by adding an intersect entity between name and fax entities The new intersect entity faxname contains two attributes fax_num and rec_num The primary key for the entity is a com posite of both attributes Individually each attribute is a foreign key that ref
575. t professional quality used by National League catalog_num 10005 stock_num 3 manu_code HSK cat_advert High Technology Design Expands the Sweet Spot cat_descr Pro style wood Available in sizes 31 32 33 34 35 catalog_num 10008 stock_num 4 manu_code HRO cat_advert Highest Quality Football for High School and Collegiate Competitions cat_descr NFL style pigskin catalog_num 10012 stock_num 6 manu_code SMT cat_advert High Visibility Tennis Day or Night cat_descr Soft yellow color for easy visibility in sunlight or artificial light catalog_num 10043 stock_num 202 manu_code KAR cat_advert High Quality Woods Appropriate for High School Competitions or Serious Amateurs cat_descr Full set of woods designed for precision control and power performance catalog_num 10045 stock_num 204 manu_code KAR cat_advert High Quality Beginning Set of Irons Appropriate for High School Competitions cat_descr Ideally balanced for optimum control Nylon covered shaft catalog_num 10068 stock_num 310 manu_code ANZ cat_advert High Quality Kickboard cat_descr White Standard size Query Result 2 36 Composing Simple SELECT Statements 2 45 Single Table SELECT Statements Expressions and Derived Values You are not limited to selecting columns by name You can use the SELECT clause of a SELECT statement to perform computations on column data and to display information derived from the contents of one or more
576. t the procedure is stored in the database so they can execute it Creating and Using Stored Procedures To write a stored procedure put the SQL statements that you want run as part of the procedure inside the statement block in a CREATE PROCEDURE state ment You can use SPL statements to control the flow of the operation within the procedure SPL statements include IF FOR and others and are described 14 4 Creating and Using Stored Procedures Creating and Using Stored Procedures in the Informix Guide to SQL Syntax The CREATE PROCEDURE and CREATE PROCEDURE FROM statements are also described in Chapter 1 of the Informix Guide to SQL Syntax Creating a Procedure Using DB Access Figure 14 1 To create a stored procedure using DB Access issue the CREATE PROCEDURE statement including all the statements that are part of the procedure in the statement block For example to create a procedure that reads a customer address you can use a statement such as the one in Figure 14 1 CREATE PROCEDURE read_address lastname CHAR 15 one argument RETURNING CHAR 15 CHAR 15 CHAR 20 CHAR 15 CHAR 2 CHAR 5 6 items DEFINE p_lname p_fname p_city CHAR 15 define each procedure variable DEFINE p_add CHAR 20 DEFINE p_state CHAR 2 DEFINE p_zip CHAR 5 SELECT fname addressl city state zipcode INTO p_fname p_add p_city p_state p_zip FROM customer WHERE lname lastname RETURN p_fname lastname p_add
577. t value for a column with a specific default associated with it e It generates a null value for any column that allows nulls but does not specify a default value for any column that specifies null as the default value This means that you must list and supply values for all columns that do not specify a default value or do not permit nulls However you can list the col umns in any order as long as the values for those columns are listed in the same order For information about setting a default value for a column see Chapter 9 Implementing Your Data Model After the INSERT statement is executed the following new row is inserted into the stock table stock_num manu_code description unit_price unit unit_descr 115 SHM tyre pump 114 Both the unit and unit_descr are blank indicating that null values are in those two columns Because the unit column permits nulls one can only guess the number of tire pumps that were purchased for 114 Of course if a default value of box was specified for this column then box would be the unit of measure In any case when inserting values into specific columns of a table pay attention to what data is needed for that row Multiple Rows and Expressions The other major form of the INSERT statement replaces the VALUES clause with a SELECT statement This feature allows you to insert the following data e Multiple rows with only one statement a row is inserted for each row r
578. t_calls table defaults to the login name of the user if no name is entered Check constraint The check constraint specifies conditions on data inserted into a column Each row inserted into a table must meet these conditions For example the quantity column of the items table may check for quantities greater than or equal to 1 For more information on using semantic integrity constraints in database design refer to Defining the Domains on page 9 3 Referential Integrity Referential integrity refers to the relationship between tables Because each table in a database must have a primary key it is possible that this primary key appears in other tables because of its relationship to data within those tables When a primary key from one table appears in another table it is called a foreign key Foreign keys join tables and establish dependencies between tables Tables can form a hierarchy of dependencies in such a way that if you change or delete a row in one table you destroy the meaning of rows in other tables For example in Figure 4 1 the customer_num column of the customer table is a primary key for that table and a foreign key in the orders and cust_call tables Customer number 106 George Watson is referenced in both the orders and cust_calls tables If customer 106 is deleted from the customer table the link between the three tables and this particular customer is destroyed When you delete a row containing a primary k
579. ta model is to identify and define your principal data objects The principal data objects are entities rela tionships and attributes Discovering Entities An entity is a principal data object that is of significant interest to the user It is usually a person place thing or event to be recorded in the database If the data model were a language entities would be its nouns The stores6 database contains the following entities customer orders items stock catalog cust_calls call_type manufact and state The first step in modeling is to choose the entities to record Most of the entities that you choose will become tables in the model 8 4 Building Your Data Model Identifying and Defining Your Principal Data Objects Choosing Possible Entities If you have an idea for your database you can probably list several entities immediately However if other people use the database you should poll them for their understanding of what fundamental things the database should contain Make a preliminary list of all the entities you can identify Interview the potential users of the database for their opinions about what must be recorded in the database Determine basic characteristics for each entity such as there must be at least one address associated with a name All of the decisions you make in determining your entities become your busi ness rules The section The Telephone Directory Example on page 8 6 provides som
580. tabid SELECT tabid FROM systables WHERE tabname orders Data Integrity The output of the query resembles the following display grantor grantee tabid tabauth tfecit mutator 101 su i x tfecit procrustes 101 s idx tfecit public 101 s i x The grantor is the user who grants the privilege The grantor is usually the owner of the table but can be another user empowered by the grantor The grantee is the user to whom the privilege is granted and the grantee public means any user with Connect privilege If your user name does not appear you have only those privileges granted to public The tabauth column specifies the privileges granted The letters in each row of this column are the initial letters of the privilege names except that i means Insert and x means Index In this example public has Select Insert and Index privileges Only the user mut ator has Update privileges and only the user procrustes has Delete privileges Before the database server performs any action for you for example execute a DELETE statement it performs a query similar to the preceding one If you are not the owner of the table and if it cannot find the necessary privilege on the table for your user name or for public it refuses to perform the operation Data Integrity The INSERT UPDATE and DELETE statements modify data in an existing database Whenever you modify existing data the integrity of the data can be affected
581. tatement This column is to have unique integer values installed Figure 6 6 shows the INFORMIX ESOLI C code needed to accomplish these things exec sql begin declare section char dcol 80 short dcolint int sequence exec sql end declare section exec sql declare target_row cursor for select datcol into dcol dcolint from target for update of serials exec sql begin work exec sql open target_row if sqlca sqlcode 0 exec sql fetch next target_row for sequence 1 sqlca sqlcode 0 sequence if dcolint lt 0 null datcol exec sql delete where current of target_row else exec sql update target set serials sequence where current of target_row if sqlca sqlcode gt 0 exec sql commit work else exec sql rollback work Cleaning up a table using an update cursor A program can execute the INSERT DELETE and UPDATE statements as described in Chapter 4 Modifying Data A program also can scan through a table with a cursor updating or deleting selected rows It also can use a cur sor to insert rows with the benefit that the rows are buffered and sent to the database server in blocks In all these activities the program must take pains to detect errors and return the database to a known state when one occurs The most important tool for doing this is the transaction Without transaction logging the program has a more difficult time recovering from errors Modifying Data Through SQL
582. tatus gt 0 THEN no error on first delete DELETE FROM orders WHERE order_num o_num END IF IF status gt 0 THEN no error on either delete COMMIT WORK ELSE problem on some delete DISPLAY Error status deleting ROLLBACK WORK END IF A fragment of 4GL that deletes from two tables The logic of this program is much the same regardless if transactions are used If they are not used the person who sees the error message has a much more difficult set of decisions to make Depending on when the error occurred one of the following situations applies No deletions were performed all rows with this order number remain in the database Some but not all item rows were deleted an order record with only some items remains e Allitem rows were deleted but the order row remains e All rows were deleted In the second and third cases the database is corrupted to some extent it contains partial information that can cause some queries to produce wrong answers You must take careful action to restore consistency to the information When transactions are used all these uncertainties are prevented 6 6 Modifying Data Through SQL Programs Using DELETE Deleting with a Cursor You can also write a DELETE statement through a cursor to delete the row that was last fetched This lets you program deletions based on conditions that Figure 6 2 A Cc annot be tested in a WHERE clause as
583. tax in expression 1 4445 use in expression 1 445S ABSOLUTE keyword syntax in FETCH 1 1945 use in FETCH 1 196S Access control See Privilege ACCESS FOR keywords in INFO statement 1 243S Accessing tables 12 16T ACOS function syntax in expression 1 458S use in expression 1 460S Action clause AFTER 1 117S definition of 1 116S FOR EACH ROW 1 116S subset syntax 1 121S syntax 1 116S Action statements in triggered action clause 1 1225 list of 1 122S order of execution 1 1225 Active set constructing with OPEN 1 2645 1 265S definition of 2 29T of a cursor 5 24T retrieving data with FETCH 1 194S 2 Index ADD CONSTRAINT keywords syntax in ALTER TABLE 1 15S AFTER action 1 117S keyword 1 117S Aggregate function ALL keyword syntax 1 462S and GROUP BY clause 3 5T AVG function syntax 1 462S description of 2 53T DISTINCT keyword syntax 1 462S in ESQL 1 467S 5 14T in EXISTS subquery 1 414S in expressions 1 314S in SELECT 1 315S in SPL expressions 14 21T in subquery 3 36T MAX function syntax 1 4625 MIN function syntax 1 462S null value signalled 5 12T restrictions in modifiable view 11 24T restrictions with GROUP BY 1 334S SUM function syntax 1 462S summary 1 465S Algebraic functions ABS function 1 445S MOD function 1 446S POW function 1 446S ROOT function 1 446S ROUND function 1 446S SORT function 1 447S syntax 1 4445 TRUNC function 1 447S Alias for a table in SELECT 1 323S for table name 2 79T to assign colum
584. te dept_num NULL NULL 0 Less dramatic but equally necessary changes of privilege are required daily or even hourly in any model that contains sensitive data If you anticipate this need you can prepare some automated tools to help maintain privileges Your first step should be to specify privilege classes that are based on the jobs of the users not on the structure of the tables For example a first line manager needs the following privileges The Select and limited Update privilege on the hypothetical hr_data table The Connect privilege to this and other databases Some degree of privilege on several tables in those databases When the manager is promoted to a staff position or sent to a field office you must revoke all those privileges and grant a new set of privileges Define the privilege classes you support and for each class specify the databases tables and columns to which you must give access Then devise two automated procedures for each class one to grant the class to a user and one to revoke it Automating with INFORMIX 4GL The mechanism you use depends on your operating system and other tools If you are a programmer the most flexible tool is probably INFORMIX 4GL 4GL makes it quite easy to program a simple user interaction as shown in the following fragment DEFINE mgr_id char 20 PROMPT What is the user id of the new manager FOR mgr_id CALL table_grant SELECT hr_data mgr_id
585. tection 1 371S 7 14T DEALLOCATE DESCRIPTOR statement syntax 1 143S with concatenation operator 1 432S DEC data type See DECIMAL data type DECIMAL data type changing data types 3 23R description of 3 11R fixed point 9 10T floating point 3 11R 9 10T signalled in SQLAWARN 5 12T syntax 1 425S using as default value 1 195 1 895 Decimal point as delimiter in DATETIME 3 9R as delimiter in INTERVAL 3 15R DECLARE statement cursor characteristics 1 149S cursor types 1 148S cursors with prepared statements 1 154S cursors with transactions 1 155S definition and use hold cursor 1 150S insert cursor 1 149S 1 157S procedure cursor 1 148S scroll cursor 1 149S select cursor 1 148S sequential cursor 1 149S update cursor 1 1485 1 1525 description of 5 20T FOR INSERT clause 6 8T FOR UPDATE 6 15T insert cursor 1 148S insert cursor with hold 1 157S procedure cursor 1 1485 restrictions with SELECT with ORDER BY 1 340S SCROLL keyword 5 23T syntax 1 145S update cursor 1 1485 updating specified columns 1 153S use with concatenation operator 1 432S with FOR UPDATE keywords 1 148S WITH HOLD clause 7 19T with SELECT 1 321S Default assumptions for your environment 4 6R DEFAULT keyword 1 169S in the CONNECT statement 1 465 Default value description of 4 19T specifying with ALTER TABLE 1 19S with CREATE TABLE 1 888 Deferred checking 1 3495 DEFERRED keyword in the SET CONSTRAINTS statement 1 349S DEFINE statement in stored procedur
586. ted with zero names That is should it be possible for an address to exist when no names use it You decide that yes it can Below address and opposite name you write 0 n as shown in the following figure name address Vv name none 0 n 0 1 If you decide that an address could not exist without being associated with at least one name you write 1 n instead of 0 n When the cardinality of a relationship is limited on either side to 1 itis a 1 n relationship In this case the relationship between names and addresses is a 1 n relationship Now consider the next cell the relationship between a name and a voice number How many voice numbers can a name be associated with one or more than one Glancing at your telephone directory you see that you may often have noted more than one telephone number for a person for some busy salesman you have a home number an office number a paging number 8 12 Building Your Data Model Identifying and Defining Your Principal Data Objects and a car phone number But there also can be names without associated numbers You write 0 n opposite name and below number voice as shown in the following figure name address number voice name none 0 n 0 1 0 n What is the other side of this relationship How many names can be associated with a voice number You decide that only one name can be asso ciated with a voice number Can a number be associated with ze
587. tem Configurations 12 4 A Single User Configuration 12 4 A Local Multiuser Configuration 12 6 A Remote Configuration 12 8 Single Machine Configuration Using Network Communication 12 9 Distributed Databases 12 10 Distributed Databases Using Multiple Vendor Servers 12 11 Connecting to Data on a UNIX Network 12 12 Example of Client Server Connections 12 13 Environment Variables 12 14 Connection Information 12 15 SQL Connection Statements 12 16 Accessing Tables 12 16 Using Synonyms with Table Names 12 17 Synonym Chains 12 18 Protecting Your Data in a Networked Environment 12 19 Table of Contents xiii Chapter 13 xiv Table of Contents Data Protection with INFORMIX SE 12 19 Data Protection with INFORMIX OnLine Dynamic Server 12 19 Data Integrity for Distributed Data 12 20 Summary 12 21 Optimizing Your Queries Chapter Overview 13 3 Optimizing Techniques 13 4 Verifying the Problem 13 4 Considering the Total System 13 5 Understanding the Application 13 5 Measuring the Application 13 6 Finding the Guilty Functions 13 7 Keeping an Open Mind 13 7 The Query Optimizer 13 8 How the Optimizer Works 13 8 Reading the Plan 13 12 Time Costs of a Query 13 14 Activities in Memory 13 14 Disk Access Management 13 14 The Cost of Reading a Row 13 16 The Cost of Sequential Access 13 17 The Cost of Nonsequential Access 13 18 The Cost of Rowid Access 13 18 The Cost of Indexed Access 13 18 The Cost of Small Tables 13 19 The Cost of NLS Functio
588. tem descriptor area 1 1645 assigning values to 1 354S modifying contents 1 3545 resizing 1 355S use with EXECUTE statement 1 187S System name in database name 1 4225 SYSTEM statement syntax 2 40S Index 43 44 Index T Table adding a constraint 1 295 alias in SELECT 1 323S ANSI compliant naming 1 507S bottleneck 10 35T candidate keys defined 8 23T changing the data type of a column 3 23R checking with the CHECK TABLE statement 1 375 composite key defined 8 23T contained in one dbspace 10 5T creating a synonym for 1 80S a table 1 845 9 24T a temporary table 1 100S dedicated device for 10 6T description of 1 11T dropping a constraint 1 325 a synonym 1 177S a table 1 179S engine response to locked table 1 370S extent sizes of 10 8T fixed length rows 10 13T in mirrored storage 10 6T in relational model 1 11T 8 20T interleaved dbspaces 10 10T joins in Condition segment 1 331S loading data with the LOAD statement 1 255S lock 7 7T locking changing mode 1 335 with ALTER INDEX 1 135 with LOCK TABLE 1 260S logging 1 104S multiple access arms for 10 7T names 12 16T names synonyms 12 17T naming conventions 1 845 1 470S 1 507S naming with NLS 1 15R optimizing queries 1 3945 ownership 11 7T primary key in 8 22T primary key defined 8 22T relation to dbspace 10 6T repairing with REPAIR TABLE statement 1 299S represents an entity 8 22T restoring with audit trail 1 2925 structure in stores6 database A 2R sy
589. tement In databases 4 24 Modifying Data Archives and Logs that are created with the MODE ANSI option no need exists to mark the beginning of a transaction One is always in effect you indicate only the end of each transaction In both styles you specify the end of a successful transaction by executing the COMMIT WORK statement This statement tells the database server that you reached the end of a series of statements that must succeed together The database server does whatever is necessary to make sure that all modifications are properly completed and committed to disk It is also possible for a program to cancel a transaction deliberately It does so by executing the ROLLBACK WORK statement This statement asks the database server to cancel the current transaction and undo any changes For example an order entry application can use a transaction when creating a new order in the following ways e Accept all data interactively e Validate and expand it Wait for the operator to make a final commitment e Execute BEGIN WORK Insert rows in the orders and items tables checking the error code returned by the database server e If there were no errors execute COMMIT WORK otherwise execute ROLLBACK WORK If any external failure prevents the transaction from being completed the partial transaction rolls back when the system restarts In all cases the data base is in a predictable state Either the new order is complet
590. tential problems e The optimizer can make different choices in a small database than ina large one even when the relative sizes of tables are the same Verify that the query plan is the same in the real and the model databases e Execution time is rarely a linear function of table size Sorting time for example increases faster than table size as does the cost of indexed access when an index goes from two to three levels What appears to be a big improvement in the scaled down environment can be insignificant when applied to the full database Therefore any conclusion you reach as a result of tests in the model database must be tentative until verified in the large one Studying the Data Model Study the definitions of all the tables views and indexes used in the data base You can examine these details interactively using the Table option of DB Access or INFORMIX SQL Pay particular attention to the indexes that exist to the data types of columns used in join conditions and for ordering and to the presence of views This chapter is written assuming that you can not change the data model Nevertheless the better you understand it the better you can understand the query plans chosen by the optimizer For information on data types and views see Chapter 9 Implementing Your Data Model 13 28 Optimizing Your Queries Making Queries Faster Studying the Query Plan Use the output from SET EXPLAIN ON to determine the
591. ter 1 1415S 5 12T syntax 1 140S using with program variables 1 141S See also Database Name segment Database level privilege description of 1 232S 4 15T granting 1 2325 passing grant ability 1 237S revoking 1 303S See also Privilege DATE data type converting to DATETIME 3 25R description of 3 7R 9 12T functions in 1 454S 2 56T in ORDER BY sequence 2 14T range of operations 3 25R representing DATE values 3 29R syntax 1 425S using with DATETIME and INTERVAL values 3 28R DATE function as time function 2 56T syntax in expression 1 4545 use in expression 1 455S 2 61T DATE value setting DBDATE environment variable 4 16R specifying European format with DBDATE 4 17R DATETIME data type 4GL example 13 6T adding or subtracting INTERVAL values 3 27R as quoted string 1 498S character string values 3 10R converting to DATE 3 25R description of 9 12T displaying format 2 61T 9 16T field qualifiers 3 8R 1 428S functions on 2 56T in expression 1 4415 INSERT 1 498S ORDER BY sequence 2 14T relational expressions 2 29T multiplying values 3 26R precision and size 3 8R 9 13T range of expressions 3 26R range of operations with DATE and INTERVAL 3 25R representing DATETIME values 3 29R syntax 1 4255 1 4885 using the DBTIME environment variable 4 27R with EXTEND function 3 26R 3 28R See also Literal DATETIME DATETIME Field Qualifier segment 1 4285 DATETIME formats using the DBTIME environment
592. tes tables indexes and views in the way you defined them You might use such a procedure to set up a training database environment Your procedure might include the creation of one or more tables and associated indexes as shown in Figure 11 7 CREATE DBA PROCEDURE all_objects CREATE TABLE learnl intone SERIAL inttwo INT NOT NULL charcol CHAR 10 CREATE INDEX learn_ix ON learnl inttwo CREATE TABLE toys name CHAR 15 NOT NULL UNIQUE description CHAR 30 on_hand INT END PROCEDURE Figure 11 7 DBA mode procedure that adds tables and indexes to the database To use the all_objects procedure to control additions of columns to tables revoke the Resource privilege on the database from all users When users try to create a table index or view using an SQL statement outside your proce dure they cannot do so When users execute the procedure they have a tem porary DBA privilege so the CREATE TABLE statement for example succeeds and you are guaranteed that every column added has a constraint placed on it In addition objects created by users are owned by that user For the all_objects procedure the two tables and the index are owned by whoever executed the procedure Using Views A view is a synthetic table You can query it as if it were a table and in some cases you can update it as if it were a table However it is not a table rather it is a synthesis of the data that exists in real tables and other views
593. tes that violate referential integrity You can always preserve referential integrity by deleting all foreign key rows before you delete the primary key to which they refer If you are imposing ref erential constraints on your database the database server does not permit you to delete primary keys with matching foreign keys It also does not 8 24 Building Your Data Model Translating E R Data Objects Into Relational Constructs permit you to add a foreign key value that does not reference an existing primary key value Referential integrity is discussed in Chapter 4 Modifying Data Adding Keys to the Telephone Directory Diagram The initial choices of primary and foreign keys is shown in Figure 8 12 This diagram reflects some important decisions For the name table the primary key rec_num is chosen Note that the data type for rec_num is SERIAL The values for rec_num are system generated If you look at the other columns or attributes in the name table you see that the data types associated with the columns are mostly character based None of these columns alone are good candidates for a primary key If you combine elements of the table into a composite key you create an exceedingly cumber some key By using a SERIAL data type you have a key that you can also use to join the other tables to the name table For the voice fax and modem tables the telephone numbers are shown as primary keys Note that these tables are
594. th INFORMIX OnLine Dynamic Server When the OnLine database server creates a database it sets up records that show the existence of the database and its mode of logging It manages disk space directly so these records are not visible to operating system commands Avoiding Name Conflicts Normally only one copy of OnLine is running on a machine and it manages the databases that belong to all users of that machine It keeps only one list of database names The name of your database must be different from that of any other database managed by that database server It is possible to run more than one copy of the database server This is sometimes done for exam ple to create a safe environment for testing apart from the operational data In that case you must be sure you are using the correct database server when you create the database and again when you access it later Implementing Your Data Model 9 21 Creating the Database Selecting a Dbspace OnLine offers you the option of creating the database in a particular dbspace A dbspace is a named area of disk storage Ask your OnLine administrator whether you should use a particular dbspace The administrator can put a database in a dbspace to isolate it from other databases or to locate it on a par ticular disk device Chapter 10 Tuning Your Data Model discusses dbspaces and their relationship to disk devices Some dbspaces are mirrored duplicated on two different disk de
595. th IS keyword 1 327S NOT operator condition 1 405S NOT relational operator 2 32T NOT WAIT keywords in SET LOCK MODE 1 370S NULL keyword ambiguous as procedure variable 1 480S NULL relational operator 2 35T NULL value testing in BYTE expression 3 5R testing with TEXT data type 3 21R Null value checking for in SELECT 1 1845 1 318S defined 8 23T detecting in ESQL 5 15T in INSERT statement 4 7T in SPL IF statement 2 255 inserting with the VALUES clause 1 252S restrictions in primary key 8 22T returned implicitly by stored procedure 2 38S specifying as default value 1 205 testing for 2 35T updating a column 1 387S used in Condition with NOT operator 1 405S used in the ORDER BY clause 1 339S with logical operator 2 36T with SPL WHILE statement 2 465 NUMERIC data type See DECIMAL data type NVARCHAR data type description of 3 18R 9 15T syntax 1 425S versus VARCHAR data type 1 19R O OF keyword syntax in DECLARE 1 145S use in DECLARE 1 153S OLD keyword in DELETE REFERENCING clause 1 119S in INSERT REFERENCING clause 1 119S in UPDATE REFERENCING clause 1 120S ON DELETE CASCADE keyword DELETE trigger event 1 1125 ON EXCEPTION statement placement of 2 325 scope of control 14 29T syntax 2 318 trapping errors 14 27T user generated errors 14 30T ON keyword syntax in CREATE INDEX 1 635 in GRANT 1 231S in REVOKE 1 300S use in CREATE INDEX 1 645 in GRANT 1 237S ON Archive utility using the ARC_DEFAULT environment
596. th audit trails 1 645 COBOL 5 6T Codd E F 1 11T 8 4T 8 32T Code set for crtcmap text file 5 6R mapping non standard to standard 5 5R mapping with crtcmap utility 5 5R Collation COLLCHAR environment variable 4 45R LC_COLLATE environment variable 4 50R simultaneous and performance 1 20R with NLS activated 1 15R Collation order and NLS 2 25T COLLCHAR environment variable 1 16R 4 45R Colon as delimiter in DATETIME 3 9R as delimiter in INTERVAL 3 15R Color setting INFORMIXTERM for 4 38R Column changing data type 3 23R creating with NLS 1 19R defined 2 5T defining 8 20T defining as foreign key 1 935 defining as primary key 1 93S description of 1 12T displaying information for 1 2425 in relational model 1 12T 8 20T in stores6 database A 2R to A 6R inserting into 1 246S label on 3 48T modifying with ALTER TABLE 1 278 naming conventions 1 875 1 1025 1 294S naming allowable characters 1 469S naming in ALTER TABLE 1 17S naming in CREATE TABLE 1 87S number allowed when defining constraint 1 865 putting a constraint on 1 86S referenced and referencing 1 225 1 94S renaming 1 294S specifying check constraint for 1 98S specifying with CREATE TABLE 1 875 virtual 1 137S See also Constraint See also Data Type segment Column expression in SELECT 1 314S syntax 1 433S See also Expression segment Column filter See Filter expression Column name allowable characters 1 469S in UPDATE clause 1 1145 naming in ALTER T
597. that depend on all the rows selected and return information about rows not the rows themselves You cannot use these functions with TEXT or BYTE columns Aggregates often are used to summarize information about groups of rows in a table This use is discussed in Chapter 3 Composing Advanced SELECT Statements When you apply an aggregate function to an entire table the result contains a single row that summarizes all of the selected rows Query 2 45 counts and displays the total number of rows in the stock table SELECT COUNT FROM stock Query 2 45 count 73 Query Result 2 45 Composing Simple SELECT Statements 2 53 Single Table SELECT Statements Query 2 46 includes a WHERE clause to count specific rows in the stock table in this case only those rows that have a manu_code of SHM SELECT COUNT FROM stock WHERE manu_code SHM Query 2 46 count 16 Query Result 2 46 By including the keyword DISTINCT or its synonym UNIQUE and a column name in Query 2 47 you can tally the number of different manufacturer codes in the stock table SELECT COUNT DISTINCT manu_code FROM stock Query 2 47 count Query Result 2 47 Query 2 48 computes the average unit_price of all rows in the stock table SELECT AVG unit_price FROM stock Query 2 48 avg Query Result 2 48 2 54 Composing Simple SELECT Statements Single Table SELECT Statements Quer
598. that stores only 9 12 Implementing Your Data Model Figure 9 3 Defining the Domains M D Y D M Y Choosing a Date Format You can punctuate and order the components of a date in many ways When an Informix database server displays a DATE value it refers to a format defined to the operating system usually in a variable named DBDATE The numbers for day month and year can be shown in any order separated by a chosen delimiter For more information see Chapter 4 of the Informix Guide to SQL Reference a year only a month and day a date and time that is exact to the hour or even to the millisecond The size of a DATETIME value ranges from 2 to 11 bytes depending on its precision as shown in Figure 9 3 The advantage of DATETIME is that it can store dates more precisely than to the nearest day and it can store time values Its sole disadvantage is an inflex ible display format but this can be circumvented see Forcing the Format of a DATETIME or INTERVAL Value on page 9 16 Precision Size Precision Size year to year 3 day to hour 3 year to month 4 day to minute 4 year to day 5 day to second 5 year to hour 6 day to fraction f 5 f 2 year to minute 7 hour to hour 2 year to second 8 hour to minute 3 year to fraction f 8 f 2 hour to second 4 month to month 2 hour to fraction f 4 f 2 month to day 3 minute to minute 2 month to hour 4 minute to second 3 month to minute 5 minute to fraction f 3 f 2 month to sec
599. the database server processes the CREATE TRIGGER statement it returns an error 15 6 Creating and Using Triggers Using Triggered Actions Using Triggered Actions To use triggers effectively you need to understand the relationship between the triggering statement and the resulting triggered actions You define this relationship when you specify the time that the triggered action occurs that is BEFORE AFTER or FOR EACH ROW Using BEFORE and AFTER Triggered Actions Triggered actions that occur before or after the trigger event execute only once A BEFORE triggered action executes before the triggering statement that is before the occurrence of the trigger event An AFTER triggered action executes after the action of the triggering statement is complete BEFORE and AFTER triggered actions execute even if the triggering statement does not process any rows Among other uses you can use BEFORE and AFTER triggered actions to determine the effect of the triggering statement For example before updat ing the quantity column in the items table you could call the stored proce dure upd_items_p1 shown in the following example to calculate the total quantity on order for all items in the table Notice that the procedure stores the total in a global variable called old_qty CREATE PROCEDURE upd_items_pl DEFINE GLOBAL old_qty INT DEFAULT 0 LET old_qty SELECT SUM quantity FROM items END PROCEDURE After
600. the examples although SQL is not case sensitive Composing Simple SELECT Statements 2 3 Introducing the SELECT Statement Introducing the SELECT Statement The SELECT statement is constructed of clauses that let you look at data ina relational database These clauses let you select columns and rows from one or more database tables or views specify one or more conditions order and summarize the data and put the selected data in a temporary table This chapter shows how to use five SELECT statement clauses You must include these clauses in a SELECT statement in the following order 1 SELECT clause 2 FROM clause 3 WHERE clause 4 ORDER BY clause 5 INTO TEMP clause Only the SELECT and FROM clauses are required These two clauses form the basis for every database query because they specify the tables and columns to be retrieved e Adda WHERE clause to select specific rows or create a join condition e Add an ORDER BY clause to change the order in which data is produced Add an INTO TEMP clause to save the results as a table for further queries Two additional SELECT statement clauses GROUP BY and HAVING enable you to perform more complex data retrieval They are introduced in Chapter 3 Composing Advanced SELECT Statements Another clause INTO is used to specify the program or host variable to receive data from a SELECT statement in the INFORMIX 4GL and SQL APIs Complete syntax and rules for using the SELECT st
601. the state column Query Result 2 26 shows the results in order of state SELECT order_num FROM orders WHERE paid_date IS NULL ORDER BY customer_num customer_num po_num ship_date Query 2 27 Composing Simple SELECT Statements 2 35 Single Table SELECT Statements order_num customer_num po_num ship_date 1004 106 8006 05 30 1993 1006 112 913557 1007 117 278693 06 05 1993 1012 117 278701 06 29 1993 1016 119 PC6782 07 12 1993 1017 120 DM354331 07 13 1993 Query Result 2 27 Forming Compound Conditions You can connect two or more comparison conditions or Boolean expressions by using the logical operators AND OR and NOT A Boolean expression eval uates as true or false or if null values are involved as unknown You can use TEXT or BYTE objects in a Boolean expression only when you test for a null value In Query 2 28 the operator AND combines two comparison expressions in the WHERE clause SELECT order_num customer_num po_num ship_date FROM orders WHERE paid_date IS NULL AND ship_date IS NOT NULL ORDER BY customer_num Query 2 28 Query 2 28 returns all rows that have a null paid_date and the ones that do not also have a null ship_date as shown in Query Result 2 28 order_num customer_num po_num ship_date 1004 106 8006 05 30 1993 1007 117 278693 06 05 1993 1012 117 278701 06 29 1993 1016 119 PC6782 07 12 1993 Query Result 2 28 2 36 Composing Simple SELECT Statements Sin
602. the triggering update completes you can calculate the total again to see how much it has changed The following stored procedure upd_items_p2 calculates the total of quantity again and stores the result in the local variable new_qty Then it compares new_qty to the global variable old_qty to see if Creating and Using Triggers 15 7 Using Triggered Actions the total quantity for all orders has increased by more than 50 percent If so the procedure uses the RAISE EXCEPTION statement to simulate an SQL error CREATE PROCEDURE upd_items_p2 EFINE GLOBAL old_qty INT DEFAULT 0 EFINE new_qty INT ET new_qty SELECT SUM quantity FROM items F new_qty gt old_qty 1 50 THEN RAISE EXCEPTION 746 0 Not allowed rule violation END IF END PROCEDURE aeoyg The following trigger calls upd_items_p1 and upd_items_p2 to prevent an extraordinary update on the quantity column of the items table CREATE TRIGGER up_items UPDATE OF quantity ON items BEFORE EXECUTE PROCEDURE upd_items_pl AFTER EXECUTE PROCEDURE upd_items_p2 If an update raises the total quantity on order for all items by more than 50 percent the RAISE EXCEPTION statement in upd_items_p2 terminates the trigger with an error When a trigger fails in INFORMIX OnLine Dynamic Server and the database has logging the database server rolls back the changes made by both the triggering statement and the triggered
603. ties can take a significant amount of time One is sort ing as described in Time Cost of a Sort on page 13 15 The other activity is processing comparisons using LIKE and MATCHES when they begin with wild card characters Disk Access Management Disk Pages It takes much longer to read a row from disk than to examine a row in memory The main goal of the optimizer is to reduce the amount of data that must be read from disk but it can eliminate only the most obvious inefficiencies The database server deals with disk storage in units called pages A page is a block of fixed size The same size is used for all databases managed by one database server Indexes are stored in page size units 13 14 Optimizing Your Queries Time Costs of a Query Time Cost of a Sort A sort requires in memory work as well as disk work The in memory work is proportional to c w n log n where c is the number of columns being ordered and represents the costs of extracting column values from the row and concatenating them into a sort key w is proportional to the width of the combined sort key in bytes and stands for the work of copying or comparing one sort key A numeric value for w would depend strongly on the computer hardware in use n log n is the number of comparisons that are made while sorting a table of n rows The disk work is proportional to 2 n m where n is again the number of rows The factor m represents the number of l
604. tion Figure 2 2 lists the relational operators you can use in a WHERE clause in place of a keyword to test for equality Operator Operation equals l or lt gt does not equal gt greater than gt greater than or equal to lt less than lt less than or equal to Relational operators that test for equality For CHAR expressions greater than means after in ASCII collating order where lowercase letters are after uppercase letters and both are after numer als See the ASCII Character Set chart in Chapter 1 of the Informix Guide to SQL Syntax For DATE and DATETIME expressions greater than means later in time and for INTERVAL expressions it means of longer duration You cannot use TEXT or BYTE columns in string expressions except when you test for null values You can use the preceding keywords and operators in a WHERE clause to create comparison condition queries that perform the following actions Include values Exclude values e Find a range of values Composing Simple SELECT Statements 2 29 Single Table SELECT Statements e Find a subset of values e Identify null values You can also use the preceding keywords and operators in a WHERE clause to create comparison condition queries which perform variable text searches using the following criteria e Exact text comparison Single character wildcards e Restricted single character wildcards e Variable length wildcards e Subsc
605. tion operator 1 4325 EXECUTE ON keywords syntax in GRANT 1 231S in REVOKE 1 300S use in GRANT 1 237S in REVOKE 1 300S EXECUTE PROCEDURE statement 1 1925 assigning values with 14 21T associating cursor with DECLARE 1 148S in FOREACH 2 208 in triggered action 1 122S using 14 9T with INTO keyword 1 1985 EXECUTE statement and sqlca record 1 186S description of 5 31T parameterizing a statement 1 186S syntax 1 184S USING DESCRIPTOR clause 1 1885 with concatenation operator 1 432S with USING keyword 1 186S Existence dependency 8 9T EXISTS keyword beginning a subquery 1 330S in a WHERE clause 3 33T use in condition subquery 1 4145 11 27T EXIT statement exiting a loop 14 23T syntax 2 148 EXP function syntax in expression 1 451S use in expression 1 451S Explicit temporary table 1 100S Exponential function EXP function 1 451S Exponential function See EXP function Expression date oriented 2 56T description of 2 46T display label for 2 49T in UPDATE 1 3875 ordering by 1 339S Expression segment aggregate expressions 1 4625 column expressions 1 433S combined expressions 1 4675 constant expressions 1 4365 expression types 1 4315 function expressions 1 4435 in SPL expressions 1 468S syntax 1 431S EXTEND function syntax in expression 1 454S use in expression 1 456S with DATE DATETIME and INTERVAL 3 26R 3 28R 2 56T 2 61T extension dat Intro 11R dbs Intro 11R idx Intro 11R lok 1 370S Extension checking specif
606. tly one value can be treated like a function This kind of subquery often uses an aggregate function because aggregate functions always return single values Query 3 29 uses the aggregate function MAX in a subquery to find the order_num for orders that include the maximum number of volleyball nets SELECT order_num FROM items WHERE stock_num 9 AND quantity SELECT MAX quantity FROM items WHERE stock_num 9 Query 3 29 order_num 1012 Query Result 3 29 3 36 Composing Advanced SELECT Statements Subqueries in SELECT Statements Query 3 30 uses the aggregate function MIN in the subquery to select items for which the total price is higher than 10 times the minimum price SELECT order_num stock_num manu_code total_price FROM items x WHERE total_price gt SELECT 10 MIN total_price FROM items WHERE order_num x order_num Query 3 30 order_num stock_num manu_code total_price 1003 8 ANZ 840 00 1018 307 PRC 500 00 1018 110 PRC 236 00 1018 304 HRO 280 00 Query Result 3 30 Correlated Subqueries Query 3 31 is an example of a correlated subquery which returns a list of the 10 earliest shipping dates in the orders table It includes an ORDER BY clause after the subquery to order the results because you cannot include ORDER BY within a subquery SELECT po_num ship_date FROM orders main WHERE 10 gt SELECT COUNT DISTINCT ship_date FROM orders sub WHERE sub ship
607. to a table is called the Insert privilege You control the use of a database by granting these privileges to other users or by revoking them Two groups of privileges exist that control the actions a user can perform on data These are database level privileges which affect the entire database and table level privileges which relate to individual tables In addition to these two groups procedure level privileges exist which determine who can execute a procedure Database Level Privileges The three levels of database privilege provide an overall means of controlling who accesses a database Granting and Limiting Access to Your Database 11 5 Granting Privileges Connect Privilege The least of the privilege levels is Connect which gives a user the basic ability to query and modify tables Users with the Connect privilege can perform the following functions Execute the SELECT INSERT UPDATE and DELETE statements provided that they have the necessary table level privileges e Execute a stored procedure provided that they have the necessary table level privileges e Create views provided that they are permitted to query the tables on which the views are based Create temporary tables and create indexes on the temporary tables The Users and the Public Privileges are granted to single users by name or to all users under the name of PUBLIC Any grant to the public serves as a default privilege Prior to execut
608. tributions the distributions rather than the key value can be used to estimate the number of rows that match a filter Optimizing Your Queries 13 9 The Query Optimizer Assessing Filters The optimizer first examines the expressions in the WHERE clause by looking for filters The optimizer estimates the selectivity of each filter it finds The selectivity is a number between 0 and 1 that indicates the fraction of rows the optimizer thinks the filter can pass A very selective filter that passes very few rows is assigned a selectivity near 0 a filter that passes most rows is assigned a selectivity near 1 For details on this process see Filter Selectivity Assignments on page 13 30 The optimizer also notes other information about the query such as what filter columns are indexed and whether an index is sufficient If only the val ues in an index are required INFORMIX OnLine Dynamic Server then no table read can be required it is faster to read the index pages without the data pages In addition the optimizer notes whether an index can be used to evaluate a filter For this purpose an indexed column is a column that has an index or one that is named first in a composite index Consider the following cases When an indexed column is compared to a literal a host variable or an uncorrelated subquery the database server can look up matching values in the index instead of reading the rows When an indexed column
609. ts for LOAD statement 1 257S restrictions in Boolean expression 3 5R with GROUP BY 3 5R with LIKE or MATCHES 3 5R with ORDER BY 3 5R restrictions with GROUP BY 3 7T restrictions with LIKE or MATCHES 2 37T restrictions with relational expression 2 29T selecting a BYTE column 3 5R syntax 1 425S with stored procedures 2 95 2 135 BYTE value displaying 2 11T C C shell how to set environment variables 4 5R cshre file 4 4R login file 4 4R Calculated expression restrictions with GROUP BY 1 334S See also Expression segment CALL keyword in the WHENEVER statement 1 398S 1 401S CALL statement assigning values with 14 21T executing a procedure 14 9T syntax 2 3S call_type table in stores6 database columns in A 5R Candidate key defined 8 23T Cardinality 8 9T Cardinality in relationship 8 13T Caret wildcard in Condition segment 1 411S Cartesian product basis of any join 2 71T description of 2 69T Cascading deletes defined 1 225 1 975 4 21T locking associated with 1 245 1 985 4 21T logging 1 245 1 985 4 21T restriction 1 24S 1 98S 4 22T syntax 1 215 1 945 Cascading triggers and triggering table 1 127S 1 131S description of 1 130S maximum number of 1 130S scope of correlation names 1 125S triggered actions 1 118S Catalog See System catalog Chaining synonyms 12 18T CHAR data type 9 15T changing data types 3 23R description of 3 6R in INSERT 1 4985 in relational expressions 2 29T replacing with TEXT 1
610. ttributes and entity occurrences will be translated into SQL tables joins between tables columns and rows The tables columns and rows of your database must fit the rules found in Rules for Defining Tables Rows and Columns Your data objects should fit these rules before you normalize your data objects Normalizing your data objects is accomplished by analyzing the dependencies between your entities relationships and attributes Normalizing is discussed in Normalizing Your Data Model on page 8 29 After you normalize the data model you can use SQL statements to create a database based on your data model Chapter 9 Implementing Your Data Model describes how to create your database and provides the database schema for the telephone directory example Each entity you choose is represented as a table in the model The table stands for the entity as an abstract concept and each row represents a specific indi vidual occurrence of the entity In addition each attribute of an entity is represented by a column in the table The following ideas are fundamental to most relational data model methods including the entity relationship data model By following these rules while designing your data model you will save time and effort when you normalize your model Rules for Defining Tables Rows and Columns You are already familiar with the idea of a table composed of rows and columns But you must respect the followin
611. ty 20 percent includes some SQL However this is by no means certain If you do not begin your examination of the problem with an open mind it is easy to overlook the part of a program that is consuming the most time If the sluggish operations are not due to the SQL turn to the books cited on page 13 3 If the SOL statements need attention you need to understand how to structure them so they run more efficiently Optimizing Your Queries 13 7 The Query Optimizer The Query Optimizer The optimizer component of the database server decides how to perform a query Its most important job is to decide the order in which to examine each table row To make that decision it has to decide on the most efficient way to access each table by a sequential scan of its rows by an existing index when joining tables by a temporary index built for the occasion or by sorting and it has to estimate how many rows each table contributes to the final result Optimizer design is not a science and the optimizer is one part of a database server that is under continuous development and improvement How the Optimizer Works The optimizer in Informix database servers formulates all possible query plans For each plan it estimates the number of table rows to be examined disk pages to be read and the network accesses that the plan requires It selects the plan with the lowest estimate The following sections provide a general overview of some of the ste
612. u can remove those strings to a table in which only unique copies are stored For example the customer city column contains city names Some city names are repeated down the column and most rows have some trailing blanks in the field Using the VARCHAR data type eliminates the blanks but not the duplication You can create a table named cities as shown in the following example CREATE TABLE cities city_num SERIAL PRIMARY KEY city_name VARCHAR 40 UNIQUE You can change the definition of the customer table so that its city column becomes a foreign key that references the city_num column in the cities table You must change any program that inserts a new row into customer to insert the city of the new customer into cities The database server return code in the SQLCODE field can indicate that the insert failed because of a duplicate key It is not a logical error it simply means that some existing customer is Tuning Your Data Model 10 27 Denormalizing located in that city However a 4GL program must use the WHENEVER statement to trap errors otherwise the negative value in SQLCODE terminates the program Besides changing programs that insert data you also must change all programs and stored queries that retrieve the city name They must use a join into the new cities table to obtain their data The extra complexity in pro grams that insert rows and the extra complexity in some queries is the cost of giving up
613. u use the interactive Query language option in DB Access or INFORMIX SQL You also can use SELECT statements to query on data noninteractively through INFORMIX SQL ACE reports you can embed them in a language such as INFORMIX ESQL C where they are treated as executable code or you can incorporate them in INFORMIX 4GL as part of its fourth generation language 2 10 Composing Simple SELECT Statements Single Table SELECT Statements Special Data Types The examples in this chapter use the INFORMIX OnLine Dynamic Server database server which enables database applications to include the data types VARCHAR TEXT and BYTE These data types are not available to applications that run on INFORMIX SE With the DB Access or INFORMIX SQL Interactive Editor when you issue a SELECT statement that includes one of these three data types the results of the query are displayed differently e Ifyou execute a query on a VARCHAR column the entire VARCHAR value is displayed just as CHARACTER values are displayed e If you select a TEXT column the contents of the TEXT column are displayed and you can scroll through them e Ifyou query ona BYTE column the words lt BYTE value gt are displayed instead of the actual value Differences specific to VARCHAR TEXT and BYTE are noted as appropriate throughout this chapter When Native Language Support NLS is enabled you can issue a SELECT statement that queries on NCHAR or NVARCHAR colum
614. uery 3 24 first performs an outer join on the orders and items tables retrieving information on all orders for items with a manu_code of KAR or SHM It then performs an outer join which combines this information with data from the dominant customer table Query 3 24 preserves order numbers 3 28 Composing Advanced SELECT Statements Creating Advanced Joins that the previous example eliminated returning rows for orders that do not contain items with either manufacturer code An optional ORDER BY clause reorganizes the data as shown in Query Result 3 24 customer_num lname 14 Albertson 18 Baxter 13 Beatty 03 Currie 15 Grant 23 Hanlon 23 Hanlon 25 Henry 04 Higgins 04 Higgins 04 Higgins 04 Higgins 0 Jaeger 0 Jaeger 20 Jewell 20 Jewell 1 Keyes 2 Lawson 28 Lessor 09 Miller 26 Neelie 22 O Brian 6 Parmelee 01 Pauli 24 Putnum 08 Quinn 07 Ream 02 Sadler 27 Satifer 27 Satifer 27 Satifer 19 Shorter 17 Sipes 17 Sipes 05 Vector 21 Wallack 06 Watson 06 Watson Query Result 3 24 022 019 005 002 021 023 023 023 016 012 007 018 014 004 order_num stock_num 204 301 301 202 111 202 110 105 306 101 302 manu_code quantity KAR KAR SHM KAR SHM KAR SHM SHM SHM SHM KAR NRPRPR You can state the join conditions in two ways when you apply an outer join to the result of an outer join to a third table The two subservient tables are joined but you
615. ues 1 285S syntax 1 284S use in transactions 1 285S with concatenation operator 1 432S with FLUSH 1 285S Q Qualifier field for DATETIME 3 8R 1 4285 1 488S for INTERVAL 3 13R 1 485S 1 491S Query cyclic 4 22T improving performance of 13 27T to 13 41T performance of 13 3T to 13 42T piping results to another program 1 2725 self referencing 4 22T sending results to an operating system file 1 271S sending results to another program 1 2725 stated in terms of data model 1 7T time costs of 13 14T Query optimization information statements 1 65 Query optimizer See Optimizer Query plan autoindex path 13 29T chosen by optimizer 13 11T description of 13 22T display with SET EXPLAIN 13 12T indexes in 13 26T use in analyzing performance 13 29T Question mark as placeholder in PREPARE 1 2735 naming variables in PUT 1 287S replacing with USING keyword 1 268S wildcard in Condition segment 1 411S Quoted string in expression 1 436S syntax in Condition segment 1 405S in expression 1 462S in INSERT 1 250S use in expression 1 438S in INSERT 1 498S with LIKE MATCHES keywords 1 328S See also Quoted String segment Quoted String segment DATETIME INTERVAL values as strings 1 498S syntax 1 497S wildcards 1 498S with LIKE in a condition 1 498S Quotes single and double Intro 6S R RAISE EXCEPTION statement exiting a loop 14 23T syntax 2 365 REAL data type See SMALLFLOAT data type RECOVER TABLE statement arc
616. ul in this context It is discussed in Chapter 5 Program ming with SQL You can work around the INTO TEMP clause restriction by first selecting the data you want to insert into a temporary table and then inserting the data from the temporary table with the INSERT statement Like wise the lack of an ORDER BY clause is not important If you need to ensure that the new rows are physically ordered in the table you can first select them into a temporary table and order it and then insert from the temporary table You can also apply a physical order to the table using a clustered index after all insertions are done The last restriction is more serious because it prevents you from naming the same table in both the INTO clause of the INSERT statement and the FROM clause of the SELECT statement This saves the database server from getting into an endless loop in which each inserted row is reselected and reinserted In some cases however you may want to do this For example suppose that you have learned that the Nikolus company supplies the same products as Statements That Modify Data the Anza company but at half the price You want to add rows to the stock table to reflect this Optimally you want to select data from all the Anza stock rows and reinsert it with the Nikolus manufacturer code However you cannot select from the same table into which you are inserting You can get around this restriction by selecting the data you want
617. ulls the constraint NOT NULL e If the column is not a primary key and should not allow duplicates the constraint UNIQUE e Ifthe column has a default value the constraint DEFAULT e Ifthe column has a check constraint the constraint CHECK In short the CREATE TABLE statement is an image in words of the table as you drew it in the data model diagram Figure 9 5 shows the statements for the telephone directory model whose diagram is shown in Figure 8 16 on page 8 31 9 24 Implementing Your Data Model Figure 9 5 Creating the Database CREATE TABLE name rec_num SERIAL PRIMARY KEY lname CHAR 20 fname CHAR 20 bdate DATE anniv DATE email VARCHAR 25 i CREATE TABLE child child CHAR 20 rec_num INT FOREIGN KEY i rec_num REFERENCES NAME CREATE TABLE address id_num SERIAL PRIMARY KEY rec_num INT street VARCHAR 50 20 city VARCHAR 40 10 state CHAR 5 DEFAULT CA zipcode CHAR 10 FOREIGN KEY rec_num REFERENCES name i CREATE TABLE voice vce_num CHAR 13 PRIMARY KEY vce_type CHAR 10 rec_num INT FOREIGN KEY i rec_num REFERENCES name CREATE TABLE fax fax_num CHAR 13 operfrom DATETIME HOUR TO MINUTE opertill DATETIME HOUR TO MINUTE PRIMARY KEY fax_num i CREATE TABLE faxname fax_num CHAR 13 rec_num INT PRIMARY KEY FOREIGN KEY FOREIGN KEY i fax_num rec_num fax_num REFERENCES fax rec_num REFERENCES name CREATE TABLE modem mdm
618. um BETWEEN 100 AND 301 ORDER BY catalog_num Query 2 78b 2 80 Composing Simple SELECT Statements Multiple Table SELECT Statements Query 2 78a and Query 2 78b are equivalent and retrieve the data shown in Query Result 2 78 stock_num manu_code description unit_price unit catalog_num cat_descr Newest ultralight helmet uses plastic shell channels of any helmet on the market cat_advert lead_time stock_num manu_code description unit_price unit catalog_num cat_descr Aerodynamic 110 HRO helmet 260 00 case 10033 Largest ventilation 8 5 oz Lightweight Plastic Slatted with Vents Assures Cool Comfort Without Sacrificing Protection 4 110 HSK helmet 308 00 each 10034 teardrop helmet covered with anti drag fabric Credited with shaving 2 seconds mile from winner s time in Tour de France time trial cat_advert lead_time stock_num manu_code description unit_price unit catalog_num cat_descr Combination cat_advert lead_time stock_num manu_code description unit_price unit catalog_num cat_descr TsO D Teardrop Design Endorsed by Yellow Jerseys You Can Time the Difference 5 205 HRO 3 golf balls 312 00 each 10048 fluorescent yellow and standard white HiFlier Golf Balls Case Includes Fluorescent Yellow and Standard White 4 301 HRO running shoes 42 50 each 10050 Engineered for serious training with exceptional stability Fabulous shock abs
619. um number average 1003 3 319 67 1004 4 354 00 1005 4 140 50 1006 5 89 60 1007 5 339 20 1013 4 35 95 1016 4 163 50 1017 3 194 67 1018 5 226 20 1021 4 403 50 1022 3 77 33 1023 6 513733 Query Result 3 6 If you use a HAVING clause without a GROUP BY clause the HAVING condition applies to all rows that satisfy the search condition In other words all rows that satisfy the search condition make up a single group Composing Advanced SELECT Statements 3 9 Using the GROUP BY and HAVING Clauses Query 3 7 a modified version of Query 3 6 returns just one row the average of all total_price values in the table SELECT AVG total_price average FROM items HAVING count gt 2 Query 3 7 average 270 97 Query Result 3 7 If Query 3 7 like Query 3 6 had included the nonaggregate column order_ num in the select list you would have to include a GROUP BY clause with that column in the group list In addition if the condition in the HAVING clause was not satisfied the output would show the column heading and a message would indicate that no rows were found Query 3 8 contains all the SELECT statement clauses that you can use in the Informix version of interactive SQL the INTO clause naming program or host variables is available only in an INFORMIX 4GL or an SQL API SELECT o order_num SUM i total_price price paid_date order_date span FROM orders o items i WHERE o order_date gt 01 01 92
620. unications Area SQLCODE field after opening cursor 5 20T description of 5 11T end of data on SELECT only 6 14T end of data signalled 5 17T set by DELETE 6 4T set by DESCRIBE 5 33T set by PUT FLUSH 6 11T sqida structure syntax in DESCRIBE 1 1625 in EXECUTE 1 1845 in FETCH 1 194S in OPEN 1 263S in PUT 1 2845 use in DESCRIBE 1 1645 in FETCH 1 201S in OPEN 1 269S in PUT 1 288S use with EXECUTE statement 1 186S SQLERRD array count of deleted rows 6 4T count of inserted rows 6 11T count of rows 6 14T description of 5 12T syntax of naming 5 11T SQLERROR keyword in the WHENEVER statement 1 398S SQLEXEC environment variable 4 41R sqlexecd 12 14T sqlhosts See INFORMIXDIR etc sqlhosts SQLNOTFOUND error conditions with EXECUTE statement 1 188S SQLRM environment variable 4 42R SQLRMDIR environment variable 4 43R SQLSTATE in databases that are not ANSI compliant 5 18T use with a cursor 5 21T SQLWARNING keyword in the WHENEVER statement 1 400S SORT function syntax in expression 1 444S use in expression 1 447S START DATABASE statement adding a transaction log 9 24T syntax and use 1 376S state table in stores6 database columns in A 6R Statement naming with NLS 1 15R SQL ANSI compliance and DBANSIWARN 4 15R SQL CONNECT and INFORMIXSERVER 4 37R SQL CREATE TABLE and COLLCHAR 4 46R SQL DESCRIBE and COLLCHAR 4 46R SQL editing and DBEDIT 4 18R SQL LOAD and DBDELIMITER 4 18R SQL SELECT and COLLCHAR 4 46R Ind
621. upports automatic execution of command scripts In most operating environments DB Access and INFORMIX SQL the interactive SQL tools accept commands and SQL statements to execute from the command line You can combine these two features to automate privilege maintenance 11 14 Granting and Limiting Access to Your Database Controlling Access to Data Using Stored Procedures The details depend on your operating system and the version of DB Access or INFORMIX SQL that you are using In essence you want to create a command script that performs the following functions e Takes a user id whose privileges are to be changed as its parameter e Prepares a file of GRANT or REVOKE statements customized to contain that user id Invokes DB Access or INFORMIX SQL with parameters that tell it to select the database and execute the prepared file of GRANT or REVOKE statements In this way you can reduce the change of the privilege class of a user to one or two commands Controlling Access to Data Using Stored Procedures You can use a stored procedure to control access to individual tables and columns in the database You can accomplish various degrees of access con trol through a procedure Stored procedures are fully described in Chapter 14 Creating and Using Stored Procedures A powerful feature of SPL is the ability to designate a stored procedure as a DBA privileged proce dure Writing a DBA privileged procedure you can allow us
622. using the same table unless the table itself is spread across multiple devices as suggested in the next section 10 6 Tuning Your Data Model INFORMIX OnLine Dynamic Server Disk Storage Reducing Contention Between Programs Using the Same Table Figure 10 2 A dbspace can comprise multiple chunks and each chunk can represent a different disk This permits you to assign multiple disk access arms to one table Figure 10 2 shows a dbspace distributed over multiple disks device 0x21 device 0x27 device 0x22 dbspace three_arms A dbspace distributed over three disks The dbspace named three_arms comprises chunks on three different disks Each chunk is approximately one third the size of an important heavily used table The third chunk is larger to allow for growth When multiple pro grams query the table their I O operations are distributed over the three disks reducing contention for the use of the hardware In an arrangement like this the multiple disks can act as mirrors for each other For example device 0x21 can be mirrored on 0x27 0x27 on 0x22 and 0x22 on 0x21 As long as any two devices are operational the dbspace is usable However if a single piece of hardware such as a disk controller is common to all three disks this type of mirror arrangement is still vulnerable to the failure of that component Tblspaces The total of all disk space allocated to a table is the tblspace of the table The
623. ustomer table do read the row into C look up C customer_num in index on orders customer_num for each matching row in the orders table do read the row into O if O paid_date is null then let Sum 0 look up O order_num in index on items order_num for each matching row in the items table do read the row into I let Sum Sum I total_price end for prepare an output row from C I and Sum end if end for end for A query plan using indexes in pseudocode The keys in an index are sorted so that when the first matching key is found any other rows with identical keys can be read without further searching This query plan reads only the following rows e All rows of the customer table once e All rows of the orders table once Those rows of the items table that match to pdnull rows from orders This is a huge reduction in effort compared with the plans without indexes An inverse plan reading orders first and looking up rows in customer by its index is equally effective However any plan that uses an index must read index data from disk as well as read row data It is difficult to predict the number of index pages that are read because some number of recently used index pages are retained in memory and are found there when they are needed See Disk Access Man agement on page 13 14 13 26 Optimizing Your Queries Making Queries Faster The physical order of a table also affects the cost of index use The physical or
624. utomatically includes a currency symbol The advantages of DECIMAL p s over INTEGER and FLOAT are that much greater precision is available up to 32 digits as compared to 10 for INTEGER and 16 for FLOAT and both the precision and the amount of storage required can be adjusted to suit the application The disadvantages are that arithmetic is less efficient and that many programming languages do not support numbers in this form Therefore when a program extracts a number it usually must convert it to another numeric form for processing However INFORMIX 4GL programs can use DECIMAL p s and MONEY values directly Implementing Your Data Model 9 11 Defining the Domains Whose Money Choosing a Currency Format Each nation has its own way of punctuating amounts of money When an Informix database server displays a MONEY value it refers to a currency format defined to the operating system usually in a variable named DBMONEY A currency symbol can precede or follow the amount and the decimal delimiter can be set to a period a comma or another character When in NLS mode you can set the X Open category LC_MONETARY to specify a foreign currency symbol and format For details see Chapter 4 of the Informix Guide to SQL Reference Chronological Types Informix database servers support three data types for recording time The DATE data type stores a calendar date DATETIME records a point in time to any degree of precision from a yea
625. val table identifier SELECT DBSERVERNAME server tabid FROM systables WHERE tabid lt 4 Query 2 67 server tabid montague montague montague montague BwWN ER Query Result 2 67 Composing Simple SELECT Statements 2 65 Single Table SELECT Statements Without the WHERE clause to restrict the values in the tabid the database server name would be repeated for each row of the systables table In Query 2 68 the HEX function returns the hexadecimal format of three specified columns in the customer table SELECT HEX customer_num hexnum HEX zipcode hexzip HEX rowid hexrow FROM customer Query 2 68 hexnum hexzip hexrow 0x00000065 O0x00016F86 0x00000001 0x00000066 Ox00016FA5 0x00000002 0x00000067 0x0001705F 0x00000003 0x00000068 Ox00016F4A 0x00000004 0x00000069 0x00016F46 0x00000005 Ox0000006A Ox00016F6F 0x00000006 0x0000006B 0x00017060 0x00000007 Ox0000006C Ox00016F6F 0x00000008 Ox0000006D 0x00016F86 0x00000009 OxO0000006E 0x00016F6E Ox0000000A OxO0000006F O0x00016F85 0x0000000B 0x00000070 O0x00016F46 0x0000000C 0x00000071 0x00016F49 0x0000000 0x00000072 Ox00016F6E 0x0000000 0x00000073 0x00016F49 0x0000000 0x00000074 0x00016F58 0x0000001 0x00000075 Ox00016F6F 0x0000001 0x00000076 0x00017191 0x0000001 0x00000077 Ox00001F42 0x0000001 0x00000078 0x00014C18 0x0000001 0x00000079 Ox00004DBA 0x0000001 Ox0000007A 0x0000215C 0x0000001 0x0000007B 0x00007E00 0x0000001 0x0000007C 0x00012116
626. vanced Joins retrieving information on all orders for items with a manu_code of KAR or SHM It then performs an outer join to combine this information with data from the dominant customer table An optional ORDER BY clause reorganizes the data into the form shown in Query Result 3 23 customer_num lname 4 Albertson 8 Baxter 3 Beatty 3 Currie 5 Grant 23 Hanlon 23 Hanlon 25 Henry 04 Higgins 0 Jaeger 20 Jewell 20 Jewell 1 Keyes 2 Lawson 28 Lessor 09 Miller 26 Neelie 22 O Brian 6 Parmelee 01 Pauli 24 Putnum 08 Quinn 07 Ream 02 Sadler 27 Satifer 27 Satifer 27 Satifer 19 Shorter 17 Sipes 05 Vector 21 Wallack 06 Watson Query Result 3 23 1020 1020 1017 1017 019 021 023 023 023 016 018 Composing Advanced SELECT Statements order_num stock_num 301 204 202 301 111 202 306 105 110 101 302 manu_code quantity KAR KAR KAR SHM SHM KAR SHM SHM SHM SHM KAR NPRPR 3 27 Creating Advanced Joins Outer Join for an Outer Join to a Third Table Query 3 24 creates an outer join that is the result of an outer join to a third table This third type is known as a nested outer join SELECT c customer_num lname o order_num stock_num manu_code quantity FROM customer c OUTER orders o OUTER items i WHERE c customer_num o customer_num AND o order_num i order_num AND manu_code IN KAR SHM ORDER BY lname Query 3 24 Q
627. ved to it to reduce the load on avignon You can reproduce the table on the new database server easily enough but how can you redirect all accesses to it One way is to install a synonym to replace the old table as shown in the following example DATABASE stores6 avignon EXCLUSIVE RENAME TABLE customer TO old_cust CREATE SYNONYM customer FOR stores6 db_crunch customer CLOSE DATABASE 12 18 Understanding Informix Networking Protecting Your Data in a Networked Environment When you execute a query within stores6 avignon a reference to table customer finds the synonym and is redirected to the version on the new com puter This is also true of queries executed from database server nantes The synonym in the database stores6 nantes still redirects references to customer to database stores6 avignon however the new synonym there sends the query to database stores6 db_crunch Chains of synonyms can be useful when as in this example you want to redi rect all access to a table in one operation However you should update all users databases as soon as possible so their synonyms point directly to the table You incur extra overhead in handling the extra synonyms and if any computer in the chain is down the table cannot be found It is possible to run an application against a local database and later to run the identical application against a database in another machine The program runs equally well in either case
628. vel lt mgr level AND emp dept_num mgr dept_num ORDER BY 4 Query 3 12a Query 3 12b uses a correlated subquery to retrieve and list the 10 highest priced items ordered SELECT order_num total_price FROM items a WHERE 10 gt SELECT COUNT FROM items b WHERE b total_price lt a total_price ORDER BY total_price Query 3 12b Query 3 12b returns the 10 rows shown in Query Result 3 12 order_num total_price 1018 15 00 1013 19 80 1003 20 00 1005 36 00 1006 36 00 1013 36 00 1010 36 00 1013 40 00 1022 40 00 1023 40 00 Query Result 3 12 You can create a similar query to find and list the 10 employees in the company who have the most seniority Composing Advanced SELECT Statements 3 15 Creating Advanced Joins Correlated and uncorrelated subqueries are described later in Subqueries in SELECT Statements on page 3 32 Using Rowid Values You can use the hidden rowid column in a self join to locate duplicate values in a table In the following example the condition x rowid y rowidis equivalent to saying row x is not the same row as row y Query 3 13 selects data twice from the cust_calls table assigning it the table aliases x and y SELECT x rowid x customer_num FROM cust_calls x cust_calls y WHERE x customer_num y customer_num AND x rowid y rowid Query 3 13 Query 3 13 searches for duplicate values in the customer_num column and for the
629. ver After every SQL statement SQLCODE is set to an integer value as shown in Figure 5 4 When that value is zero the statement is performed without error In par ticular when a statement is supposed to return data into a host variable a code of zero means that the data has been returned and can be used Any nonzero code means the opposite no useful data was returned to host variables In INFORMIX 4GL SOLCODE is also accessible under the name STATUS End of Data The database server sets SQLCODE to 100 when the statement is performed correctly but no rows are found Two situations exist where this can occur The first situation involves a query that uses a cursor Queries using cursors are described under Retrieving Multiple Rows on page 5 19 In these que ries the FETCH statement retrieves each value from the active set into mem ory After the last row is retrieved a subsequent FETCH statement cannot return any data When this occurs the database server sets SQLCODE to 100 which says end of data no rows found The second situation involves a query that does not use a cursor In this case the server sets SQLCODE to 100 when no rows satisfy the query condition In ANSI compliant databases SELECT DELETE UPDATE and INSERT state ments all set SOQLCODE to 100 if no rows are returned In databases that are not ANSI compliant only a SELECT statement that returns no rows causes SQLCODE to be set to 100 Negative Codes When
630. ver when you specify a SERIAL data type on a primary key in one table you specify an INTEGER on the foreign key of the relationship The SERIAL and INTEGER construction is the only data type combination that you can mix in a relationship The decision tree shown in Figure 9 1 summarizes the choices among data types They are explained in the following sections 9 4 Implementing Your Data Model Defining the Domains Data items purely yes numeric no ane all integral yes no All numbers between yes 215 and 2 5 1 no SMALLINT All numbers between yes 231 and 231 1 no INTEGER Number of fractional digits is fixed no At most 8 si digits no gnificant At most 16 significant digits no DECIMAL p y DECIMAL p 0 yes DECIMAL p s yes SMALLFLOAT yes FLOAT Figure 9 1 A diagram of the decisions to be made in choosing a data type 1 of 2 Implementing Your Data Model 9 5 Defining the Domains y Ga is chronological yes no Span of time or specific span point in time point INTERVAL Precise only to nearest yes day no DATE DATETIME Data contains yes foreign characters no No or little variance in yes item lengths ng NCHAR n NVARCHAR m r Data is ASCII characters yes no No or little variance in item lengths no Lengths under
631. ver central SELECT O order_num C fname C lname FROM masterdb central customer C sales boston orders O WHERE C customer_num O Customer_num INTO TEMP mycopy In the example two tables are being joined The joined rows are stored ina temporary table in the current database The tables are located in two data base servers central and boston Informix allows you to over qualify to give more information than is required table names so it is possible in this example that the current database is masterdb or sales Using Synonyms with Table Names A synonym is aname that you can use in place of another name The main use of the CREATE SYNONYM statement is to make it more convenient to refer to tables that are not in the current database The preceding example has been revised as shown in the following example to use synonyms for the table names CREATE SYNONYM mcust FOR masterdb central customer CREATE SYNONYM bords FOR sales boston orders SELECT bords order_num mcust fname mcust lname FROM mcust bords WHERE mcust customer_num bords Customer_num INTO TEMP mycopy Understanding Informix Networking 12 17 Accessing Tables The CREATE SYNONYM statement stores the synonym name in the system catalog table syssyntable in the current database The synonym is available to any query made within that database A short synonym makes it easier to write queries but synonyms can play another role They allow
632. vered in Chapters 8 through 11 of this manual However you may want to update and query at the same time when a database is first being developed before its design has been carefully thought through A typical problem arises when a table inad vertently and incorrectly contains a few rows with duplicate values in a col umn that should be unique You might want to delete the duplicate rows or update only the duplicate rows Either way a test for duplicate rows inevita bly requires a subquery which is not allowed in an UPDATE statement or DELETE statement Chapter 6 Modifying Data Through SQL Programs discusses how to use an update cursor to perform this kind of modification Updating with Selected Values 4 14 Modifying Data The second form of UPDATE statement replaces the list of assignments with a single bulk assignment in which a list of columns is set equal to a list of val ues When the values are simple constants this form is nothing more than the form of the previous example with its parts rearranged as shown in the following example UPDATE customer SET fname lname Barnaby Dorfler WHERE customer_num 103 No advantage exists to writing the statement this way In fact it is harder to read because it is not obvious which values are assigned to which columns However when the values to be assigned come from a single SELECT statement this form makes sense Suppose that changes of address are to be
633. vers the decisions that you must make to implement the model The first step in implementation is to complete the data model by defining a domain or set of data values for every column The second step is to implement the model using SQL statements The first section of this chapter covers defining domains in detail The second section shows how you create the database using the CREATE DATABASE and CREATE TABLE statements and populate it with data Defining the Domains To complete the data model described in Chapter 8 Building Your Data Model you must define a domain for each column The domain of a column describes the constraints on and identifies the set of valid values attributes or columns may assume The purpose of a domain is to guard the semantic integrity of the data in the model that is to ensure that it reflects reality in a sensible way If aname can be entered where a telephone number was planned or a fractional number where an integer should be the integrity of the data model is at risk You define a domain by first defining the constraints that a data value must satisfy before it can be part of the domain Column domains are specified using the following constraints e Data types Default values Check constraints In addition referential constraints can be placed on columns by identifying the primary and foreign keys in each table How to identify these keys was discussed in Chapter 8 Building Y
634. vices for high reliability your database can be put in a mirrored dbspace if its contents are of exceptional importance Choosing the Type of Logging OnLine offers the following four choices for transaction logging No logging at all This choice is not recommended if the database is lost to a hardware failure all data alterations since the last archive are lost CREATE DATABASE db_with_no_log When you do not choose logging BEGIN WORK and other SQL statements related to transaction processing are not permitted in the database This affects the logic of programs that use the database e Regular unbuffered logging This is the best choice for most databases In the event of a failure only uncommitted transactions are lost CREATE DATABASE a_logged_db WITH LOG e Buffered logging If the database is lost a few or possibly none of the most recent alterations are lost In return for this small risk performance during alterations is improves slightly CREATE DATABASE buf_log_db WITH BUFFERED LOG Buffered logging is best for databases that are updated frequently so that speed of updating is important but the updates can be re created from other data in the event of a crash You can use the SET LOG statement to alternate between buffered and regular logging 9 22 Implementing Your Data Model Creating the Database e ANSI compliant logging This is the same as regular logging but the ANSI rules for trans
635. vilege carries the same authorization as the Connect privilege In addition users with the Resource privilege can create new per manent tables indexes and stored procedures thus permanently allocating disk space Database Administrator Privilege A The highest level of database privilege is Database Administrator or DBA When you create a database you are automatically the DBA Holders of the DBA privilege can perform the following functions Execute the DROP DATABASE START DATABASE and ROLLFORWARD DATABASE statements Drop or alter any object regardless of who owns it e Create tables views and indexes to be owned by other users Grant database privileges including the DBA privilege to another user e Alter the NEXT SIZE but no other attribute of the system catalog tables and insert delete or update rows of any system catalog table except systables Warning Although users with the DBA privilege can modify the system catalog tables Informix strongly recommends that you do not update delete or alter any rows in the system catalog tables Modifying the system catalog tables can destroy the integrity of the database Ownership Rights The database and every table view index procedure and synonym in it has an owner The owner of an object is usually the person who created it although a user with the DBA privilege can create objects to be owned by others The owner of an object has all rights to th
636. wide that one row fills a page some database servers permit a row to exceed the size of a page However a typical disk page contains from 5 to 50 rows An index entry consists of a key value and a 4 byte pointer so an index page typically contains from 50 to 500 entries Page Buffers The database server has a set of memory spaces in which it keeps copies of the disk pages it read most recently It does this in case these pages are needed again If they are the database server does not have to read them from disk As with the size of a disk page the number of these page buffers depends on the database server and the host operating system The Cost of Reading a Row When the database server needs to examine a row that is not already in memory it must read it from disk It does not read only one row it reads the pages that contain the row When a row is larger than a page it reads as many whole pages as necessary The cost of reading one page is the basic unit of work that the optimizer uses for its calculations 13 16 Optimizing Your Queries Time Costs of a Query The actual cost of reading a page is variable and hard to predict It is a combination of the following factors Buffering The needed page might be in a page buffer already in which case the cost of access is near zero Contention If more than one application is contending for the use of the disk hardware the database server request can be delayed Seek time
637. ws or index key values The size of the object being locked is referred to as the scope of the lock also called the lock granularity In general the larger the scope of a lock the more concurrency is reduced but the simpler programming becomes Database Locks You can lock an entire database The act of opening a database places a shared lock on the name of the database A database is opened with the CONNECT DATABASE or CREATE DATABASE statements As long as a program has a database open the shared lock on the name prevents any other program from dropping the database or putting an exclusive lock on it You can lock an entire database exclusively with the following statement DATABASE database name EXCLUSIVE This statement succeeds if no other program has opened that database Once the lock is placed no other program can open the database even for reading because its attempt to place a shared lock on the database name fails 7 6 Programming for a Multiuser Environment How Locks Work A database lock is released only when the database closes That can be done explicitly with the DISCONNECT or CLOSE DATABASE statements or implicitly by executing another DATABASE statement Because locking a database reduces concurrency in that database to zero it makes programming very simple concurrent effects cannot happen How ever you should lock a database only when no other programs need access Database locking is often used
638. ws are returned if you select the columns of a primary key or of a candidate key Primary and candidate keys are discussed in Chapter 8 Building Your Data Model Restrictions on Views Because a view is not really a table it cannot be indexed and it cannot be the object of such statements as ALTER TABLE and RENAME TABLE The columns of a view cannot be renamed with RENAME COLUMN To change anything about the definition of a view you must drop the view and re create it Because it must be merged with the user s query the SELECT statement on which a view is based cannot contain any of the following clauses INTO TEMP The user s query might contain INTO TEMP if the view also contains it the data would not know where to go UNION The user s query might contain UNION No meaning has been defined for nested UNION clauses ORDER BY The user s query might contain ORDER BY If the view also contains it the choice of columns or sort directions could be in conflict When the Basis Changes The tables and views on which a view is based can change in several ways The view automatically reflects most of the changes When a table or view is dropped any views in the same database that depend on it are automatically dropped The only way to alter the definition of a view is to drop and re create it Therefore if you change the definition of a view on which other views depend you must also re create the other views because th
639. x 1 370S SET LOG statement buffered vs unbuffered 1 372S 9 22T syntax 1 372S SET OPTIMIZATION statement syntax and use 1 374S Setting environment variables 4 5R SHARE keyword syntax in LOCK TABLE 1 260S Shared memory network connection 12 7T Shared memory parameters specifying file with ONCONFIG 4 39R Shell setting environment variables in a file 4 4R specifying with DBREMOTECMD 4 25R Simple assignment 2 288 SIN function syntax in expression 1 458S use in expression 1 459S Single precision floating point number storage of 3 12R Singleton SELECT statement 1 3185 2 29T Site network 12 4T primary 12 20T secondary 12 20T SITENAME function returns servername 1 438S syntax in expression 1 436S in INSERT 1 250S use in ALTER TABLE 1 18S in CREATE TABLE 1 888 in expression 1 438S in INSERT 1 252S in SELECT 2 63T 2 65T 3 20T Slash arithmetic operator 1 4315 SMALLFLOAT data type changing data types 3 23R 40 Index description of 3 20R 9 9T syntax 1 425S SMALLINT data type changing data types 3 23R description of 3 20R 9 7T syntax 1 425S using as default value 1 195 1 89S SOME keyword beginning a subquery 1 330S 3 33T use in Condition subquery 1 415S Sort merge join 13 27T Sorting avoiding nonsequential access 13 37T avoiding with temporary table 13 36T effect on performance 13 33T in a combined query 1 344S in SELECT 1 337S nested 2 15T optimizer estimates cost 13 12T PSORT_DBTEM
640. xecute privilege to specific users unless you have first revoked it If you create a procedure in an ANSI compliant database no other users have the Execute privilege by default you must grant specific users the Execute privilege The following example grants the Execute privilege to the user orion so that orion can use the stored procedure named read address GRANT EXECUTE ON read_address TO orion Procedure level privileges are recorded in the sysprocauth system catalog table The sysprocauth table uses a primary key of the procedure number grantor and grantee In the procauth column the execute privilege is indi cated by a lowercase letter e If the execute privilege was granted with the WITH GRANT option the privilege is represented by an uppercase letter E For more information on procedure level privileges see Privileges on Stored Procedures on page 14 13 11 12 Granting and Limiting Access to Your Database Granting Privileges Automating Privileges It might seem that this design forces you to execute a tedious number of GRANT statements when you first set up the database Furthermore privi leges require constant maintenance as people change their jobs For example if a clerk in Human Resources is terminated you want to revoke the Update privilege as soon as possible otherwise you risk the unhappy employee executing a statement such as the following one UPDATE hr_data SET emp_name hire_da
641. xes Dropping Indexes In some applications the majority of table updates can be confined to a single time period Perhaps all updates are applied overnight or on specified dates When this is the case consider dropping all non unique indexes while you perform updates and then create new indexes afterward This can have two good effects First because fewer indexes occur to update the updating program can run faster Often the total time to drop the indexes update without them and re create them afterward is less than the time to update with the indexes in place The time cost of updating indexes is discussed under Time Costs of Indexes on page 10 20 Second newly made indexes are the most efficient ones Frequent updates tend to dilute the index structure causing it to contain many partly full leaf pages This reduces the effectiveness of an index and wastes disk space As another timesaving measure make sure that a batch updating program calls for rows in the sequence defined by the primary key index That sequence causes the pages of the primary key index to be read in order and only one time each The presence of indexes also slows down the population of tables when you use the LOAD statement or the dbload utility Loading a table that has no indexes is a very quick process little more than a disk to disk sequential copy but updating indexes adds a great deal of overhead The fastest way to load a table is as d
642. y standard query language developed by International Business Machines Corporation IBM Informix Products That Use SOL Informix produces many application development tools and SQL application programming interfaces API Application development tools currently available include products like INFORMIX SQL INFORMIX 4GL and the Interactive Debugger SQL APIs currently available include INFORMIX ESQL C and INFORMIX ESQL COBOL Informix products work with a database server either INFORMIX OnLine Dynamic Server or INFORMIX SE The DB Access database access utility is shipped as a part of each database server If you are running client applications developed with Version 4 1 and 5 0 application development tools you use INFORMIX NET to connect the client to the network Products Included in This Manual All of the information presented in this manual is valid for the following products INFORMIX ESQLI C Version 6 0 INFORMIX ESQL COBOL Version 6 0 INFORMIX SE Version 6 0 INFORMIX OnLine Dynamic Server Version 6 0 INFORMIX OnLine Optical Version 6 0 INFORMIX TP XA Version 6 0 Introduction 3 Other Useful Documentation An additional product that uses information from this manual is the INFORMIX Gateway with DRDA Version 6 0 In addition some examples in this manual are built using Informix products at earlier release levels Other Useful Documentation You can refer to a number of related
643. y 2 49 computes the average unit_price of just those rows in the stock table that have a manu_code of SHM SELECT AVG unit_price FROM stock WHERE manu_code SHM Query 2 49 avg Query Result 2 49 You can combine aggregate functions in Query 2 50 SELECT MAX ship_charge MIN ship_charge FROM orders Query 2 50 Query 2 50 finds and displays both the highest and lowest ship_charge in the orders table as shown in Query Result 2 50 max min Query Result 2 50 You can apply functions to expressions and you can supply display labels for their results as shown in Query 2 51 SELECT MAX res_dtime call_dtime maximum MIN res_dtime call_dtime minimum AVG res_dtime call_dtime average FROM cust_calls Query 2 51 Composing Simple SELECT Statements 2 55 Single Table SELECT Statements Query 2 51 finds and displays the maximum minimum and average amount of time in days hours and minutes between the reception and resolution of a customer call and labels the derived values appropriately These amounts of time are shown in Query Result 2 51 maximum minimum average 5 20 55 0 00 01 1 02 56 Query Result 2 51 Query 2 52 calculates the total ship_weight of orders shipped on July 13 1993 SELECT SUM ship_weight FROM orders WHERE ship_date 07 13 1993 Query 2 52 sum Query Result 2 52 Time Functions You can use the time functions DAY MDY
644. y and with what data In addition to these points INFORMIX OnLine Secure offers a type of automatic security called mandatory access control MAC With MAC all users and all data are assigned a security label and OnLine Secure compares the labels before allowing access For example a TOP SECRET user could view an UNCLASSIFIED row but an UNCLASSIFIED user could not view a TOP SECRET row This topic and other topics related to security in OnLine Secure are addressed in the INFORMIX OnLine Secure Security Features User s Guide Granting and Limiting Access to Your Database 11 3 Controlling Access to Databases Controlling Access to Databases The normal database privilege mechanisms are based on the GRANT and REVOKE statements They are covered in the section Granting Privileges on page 11 5 However you can sometimes use the facilities of the operating system as an additional way to control access to a database Securing Database Files Database servers other than INFORMIX OnLine Dynamic Server store databases in operating system files Typically a database is represented as a number of files one for each table one for the indexes on each table and pos sibly others The files are collected in a directory The directory represents the database as a whole Multiuser Systems You can deny access to the database by denying access to the database directory The means by which you can do this depend on your operating syste
645. y are set to either a blank or a W to indicate a variety of special conditions only six are used Their meanings depend on the statement just executed A set of warning flags appear when a database opens that is following a CONNECT DATABASE or CREATE DATABASE statement These flags tell you some characteristics of the database as a whole A second set of flags appear following any other statement These flags reflect unusual events that occur during the statement events that might not be reflected by SQLCODE Both sets of SOLAWARN values are summarized in Figure 5 5 The SQLSTATE Value Certain Informix products such as INFORMIX ESQL C and INFORMIX ESQL COBOL support the SQLSTATE value in compliance with X Open and ANSI SQL standards The GET DIAGNOSTICS statement reads the SQLSTATE value in order to diagnose errors after you run an SQL statement The database server returns a result code in a five character string that is 5 12 Programming with SQL Retrieving Single Rows stored in a variable called SOLSTATE The SOLSTATE error code or value tells you the following information about the most recently executed SQL statement e If the statement was successful e Ifthe statement was successful but generated warnings e Ifthe statement was successful but generated no data e If the statement failed For more information on GET DIAGNOSTICS the SQLSTATE variable and the meanings of the SQLSTATE return codes see the section ca
646. y labels with 3 48T restrictions in view 11 22T restrictions on use 1 344S syntax in SELECT 1 310S use in SELECT 1 344S Unique constraint dropping 1 32S modifying a column with 1 285 rules of use 1 305 1 925 1 94S UNIQUE keyword constraint in CREATE TABLE 9 24T restrictions in modifiable view 11 24T syntax in CREATE INDEX 1 635 in CREATE TABLE 1 915 in SELECT 1 3125 use in ALTER TABLE 1 295 in CREATE INDEX 1 645 in CREATE TABLE 1 925 in expression 1 462S in SELECT 1 3138 2 19T no effect in subquery 1 414S UNITS keyword syntax in expression 1 436S use in expression 1 4425 UNIX BSD default print capability 4 7R 4 24R viewing environment settings 4 5R environment variables listed 4 9R PATH environment variable 4 54R specifying directories for intermediate writes 4 40R System V default print capability 4 7R 4 24R terminfo library support 4 39R viewing environment settings 4 5R TERM environment variable 4 55R TERMCAP environment variable 4 56R TERMINFO environment variable 4 56R UNIX operating system 12 4T 12 6T UNLOAD statement DELIMITER clause 1 380S exporting data to a file 9 27T specifying field delimiter with DBDELIMITER 4 18R syntax 1 378S UNLOAD TO file 1 378S unloading VARCHAR TEXT or BYTE columns 1 379S NLOAD TO file 1 378S nloading a database 5 8R NLOCK TABLE statement syntax and use 1 381S nnamed pipes 12 7T pdatable view 1 139S PDATE clause syntax 1 114S pdate cursor 1 1485 definition of 1 14
647. y learned some method by all means use it Building Your Data Model 8 3 Identifying and Defining Your Principal Data Objects This chapter presents a summary of the entity relationship E R data model a modeling method taught in training courses presented by Informix and other companies and based on the original data model by E F Codd This modeling method is carried out in the following steps 1 Identify and define the principal data objects entities relationships and attributes Diagram the data objects using the entity relationship approach Translate your entity relationship data objects into relational constructs Resolve the logical data model g e WY N Normalize the logical data model Steps 1 5 are discussed in this chapter Chapter 9 Implementing Your Data Model discusses a final step converting your logical data model to a physical schema The end product of data modeling is a fully defined database design encoded in a diagram like that in Figure 8 16 on page 8 31 which shows the final set of tables for a personal telephone directory The personal telephone directory is an example developed in this chapter It is used rather than the stores6 database used in the rest of this book because it is small enough to be developed completely in one chapter but large enough to show the entire method Identifying and Defining Your Principal Data Objects The first step in building an entity relationship da
648. y the following features of relationships as shown in Figure 8 8 e A circle across a relationship link indicates optionality in the relationship zero instances e A small bar across a relationship link indicates that exactly one instance of the entity is associated with another entity Consider the bar as a 1 e The crow s feet represents many in your relationship Building Your Data Model 8 17 Diagramming Your Data Objects _ optionailit optionality a ea p y p y Sf pO OF a many sacle a one Figure 8 8 The parts of a relationship in an entity relationship diagram How You Read Entity Relationship Diagrams You read the diagrams first from left to right and then from right to left In the case of the name address relationship diagrammed in Figure 8 9 you read the relationships as follows names can be associated with zero or exactly one address addresses can be associated with zero one or many names can have zero or gt exactly 1 name address A pO O can have zero or many Figure 8 9 Reading an entity relationship diagram The Telephone Directory Example Figure 8 10 shows the telephone directory example and includes the entities relationships and attributes This diagram includes the relationships that were established with the matrix After studying the diagram symbols com pare the entity relationship diagram in Figure 8 10 with the matrix in F
649. year 1 p 2 hour p to minute 2 p 2 year p to month 2 p 2 hour p to second 3 p 2 month p to month 1 p 2 hour p to fraction f 4 p f 2 day p to day 1 p 2 minute p to minute 1 p 2 day p to hour 2 p 2 minute p to second 2 p 2 day p to minute 3 p 2 minute p to fraction f 3 p f 2 day p to second 4 p 2 second p to second 1 p 2 day p to fraction f 5 p f 2 second p to fraction f 24 p f 2 hour p to hour 1 p 2 fraction to fraction f 1 f 2 Round a fractional size to the next full byte All possible precisions of the INTERVAL data type with their sizes in bytes INTERVAL values can be negative as well as positive You can add or subtract them and you can scale them by multiplying or dividing by a number This is not true of either DATE or DATETIME It is reasonable to ask What is one half the number of days until April 23 but it is not reasonable to ask What is one half of April 23 9 14 Implementing Your Data Model Defining the Domains Character Types All Informix database servers support the CHAR n data type When NLS has been enabled the Informix database servers support the NCHAR n data type INFORMIX OnLine Dynamic Server also supports other special use character data types Character Data CHAR n and NCHAR n The CHAR n data type contains a sequence of n ASCII characters The length n ranges from 1 to 32 767 If you are using the INFORMIX SE database server the maximum length is 32
650. ying with DBANSIWARN 4 15R Extension to SQL symbol for Intro 75 with ANSI compliant database 1 14R Extent changing size of for system table 2 9R description of 10 8T next extent doubles 10 10T sizes of 10 8T upper limit on 10 10T EXTENT SIZE keywords 1 107S 10 8T F FETCH statement ABSOLUTE keyword 5 23T as affected by CLOSE 1 395 checking results with SQLCA 1 202S description of 5 21T fetching a row for update 1 201S locking for update 1 201S relation to GET DESCRIPTOR 1 210S sequential 5 23T specifying a value s memory location 1 198S syntax 1 194S with concatenation operator 1 432S INTO keyword 1 319S program arrays 1 199S scroll cursor 1 196S sequential cursor 1 195S 5 25T X Open mode 1 195S Field qualifier for DATETIME 3 8R 1 428S for INTERVAL 3 13R 1 4855 1 491S File compared to database 1 3T environment configuration 4 4R environment configuration checking with chkenv 5 4R extension lok 1 370S mapping and COLLCHAR 4 45R mapping and crtcmap utility 5 5R mapping and DBAPICODE 4 47R mapping format for 5 6R Index 19 20 Index permissions in UNIX 11 4T sending output with the OUTPUT statement 1 271S shell 4 4R temporary for OnLine 4 26R temporary for SE 4 27R FILE statement character position form 5 28R delimiter form 5 24R syntax for character position form 5 29R syntax for delimiter form 5 25R with dbload 5 23R Filter expression effect on performance 13 23T 13 32T 13 33T evaluated fr
651. ynamic Server The OnLine database server contains elaborate features to support archiving and logging They are described in the INFORMIX OnLine Dynamic Server Archive and Backup Guide 4 26 Modifying Data Concurrency and Locks Conceptually the facilities of OnLine are similar to those already described for INFORMIX SE but they are more elaborate for the following reasons OnLine has very stringent requirements for performance and reliability for example it supports making archive copies while databases are in use OnLine manages its own disk space that is devoted to logging e It performs logging concurrently for all databases using a limited set of log files The log files can be copied to another medium backed up while transactions are active These facilities are usually managed from a central location by the OnLine administrator so the users of the databases never have to be concerned with them If you want to make a personal archive copy of a single database or table that is held by OnLine you can do it with the onunload utility This program cop ies a table or a database to tape Its output consists of binary images of the disk pages as they were stored in OnLine As a result the copy can be made very quickly and the corresponding onload program can restore the file very quickly However the data format is not meaningful to any other programs If your OnLine administrator is using ON Archive to create a

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