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1. al bundy INSERT INTO unit VALUES cm 1 0 al bundy INSERT INTO unit VALUES m 100 0 al bundy SERT INTO unit VALUES inch 2 54 al bundy al bundy INSERT INTO shoe data VALUES al bundy shi 2 black 0 0 90 0 tom al bundy INSERT INTO shoe data VALUES al bundy sh2 0 black 30 0 40 0 inch al bundy INSERT INTO shoe data VALUES al bundy sh3 4 brown 50 0 65 0 om al bundy INSERT INTO shoe data VALUES al bundy 7sh4 3 brown 40 0 50 0 inch al bundy al bundy INSERT INTO shoelace data VALUES al bundy sii 5 plack gp 80 0 om al bundy INSERT INTO shoelace data VALUE al bundy s1277 5 black 100 0 om y al bundy INSERT INTO shoelace data VALUE al bundy sl13 0 plack r 35 0 CIRCA al bundy INSERT INTO shoelace data VALUE al bundy Pela B bhblack 20 0 tinoch J3 al bundy INSERT INTO shoelace data VALUE al bundy s197 4 brown dub my al bundy INSERT INTO shoelace data VALUE al bundy sl6 D Chrown 0 9 m al bundy INSERT INTO shoelace data VALUE al bundy sl7 7 brown 60 cm al bundy INSERT INTO shoelace data VALUE al bundy sI8 1 brown 40 incbhb al bundy al bundy SELECT FROM shoelace sl name sl avail sl color sl len sl unit sl len cm
2. end LANGUAGE plpgsql While running psq1 you can load or reload such a function definition file with Ni filename sql and then immediately issue SQL commands to test the function Another good way to develop in PL pgSQL is using PostgreSQL s GUI tool PgAccess It does some nice things for you like escaping single quotes and making it easy to recreate and debug functions 19 2 Structure of PL pgSQL PL pgSQL is a block structured language The complete text of a function definition must be a block A block is defined as lt lt label gt gt DECLARE declarations BEGIN statements END 309 Chapter 19 PL pgSQL SQL Procedural Language Any statement in the statement section of a block can be a sub block Sub blocks can be used for logical grouping or to localize variables to a small group of statements The variables declared in the declarations section preceding a block are initialized to their default values every time the block is entered not only once per function call For example CREATE FUNCTION somefunc RETURNS INTEGER AS DECLARE quantity INTEGER 30 BEGIN RAISE NOTICE Quantity here is quantity Quantity here is 30 quantity 50 Create a sub block DECLARE quantity INTEGER 80 BEGIN RAISE NOTICE Quantity here is quantity
3. seen 342 19 11 6 Appendix eee E E UE OE e ES 342 19 11 6 1 Code for my instr functions 342 20 PL Tcl Tcl Procedural Language essent nennen enne 345 20 1 OVERVIEW nei o nee ER ette PO ed deis 345 20 2 Description ote e tee eee d a ette ede e E Sanden 345 20 2 1 PL Tcl Functions and Arguments eeeseeeeeeeeeee eene 345 20 2 2 Data Values PL Tcl nane nc Rete en 346 20 2 3 Global Data in PL Tcl 2 o ete ederet 347 20 2 4 Database Access from PL Tcl sesesssseeeeeeeeeeeen eene 347 20 2 5 Trigger Procedures in PL Tcl eee esee teen 349 20 2 6 Modules and the unknown command seen 351 20 2 7 Tcl Procedure Names eenn eea roneo en aTe nennen nennen enne 351 21 PL Perl Perl Procedural Van guage iones oserei o ttt ede tei t ede 352 21 1 PL Perl Functions and Arguments enne enne 352 21 2 Data Values an BE Berl eite oerte ete Rieti erre een 353 21 3 Database Access from PL Perl essent 353 214 Trusted and Untrusted PLI Perl eet rrr tret rere s 354 21 5 Missing Features one epp eI REPERI eR 354 22 PL Python Python Procedural Language eseeeeeeeeeneeennen enne 356 22 1 PE Python Functions 2e ee Ree OTI ERR cee 356 22 25 Tigger Funet ons e ds ere t rid td e o t edens 356 22 3 Database ACCES Srna ae ede PRO AA OC EIE Bee 357 22 4 Restricted Envi
4. EXEC SQL CONNECT TO target AS connection name USER user name The target can be specified in the following ways dbname hostname port e tcp postgresql hostname port dbname options unix postgresql hostname port dbname options character variable character string DEFAULT 66 Chapter 4 ECPG Embedded SQL in C There are also different ways to specify the user name userid userid password userid IDENTIFIED BY password userid USING password The useridand password may be a constant text a character variable or a character string The connection name is used to handle multiple connections in one program It can be omitted if a program uses only one connection 4 3 Closing a Connection To close a connection use the following statement EXEC SQL DISCONNECT connection The connection can be specified in the following ways connection name DEFAUL CURREN ALL 4 4 Running SQL Commands Any SQL command can be run from within an embedded SQL application Below are some examples of how to do that Creating a table EXEC SQL CREATE TABLE foo number integer ascii char 16 EC SQL CREATE UNIQUE INDEX numl ON foo number EXEC SQL COMMIT x lt Inserting rows EXEC SQL INSERT INTO foo number ascii VALUES 9999 doodad EXEC SQL
5. 244 Chapter 14 Interfacing Extensions To Indexes Function Support Number size 3 GiST indexes require seven support functions as shown in Table 14 7 Table 14 7 GiST Support Functions Function Support Number consistent 1 union 2 compress 3 decompress 4 penalty 5 picksplit 6 equal 7 14 5 Creating the Operators and Support Routines Now that we have seen the ideas here is the promised example of creating a new operator class First we need a set of operators The procedure for defining operators was discussed in Chapter 11 For the complex abs ops operator class on B trees the operators we require are absolute value less than strategy 1 absolute value less than or equal strategy 2 absolute value equal strategy 3 absolute value greater than or equal strategy 4 absolute value greater than strategy 5 Suppose the code that implements these functions is stored in the file PGROOT src tutorial complex c which we have compiled into PGROOT src tutorial complex so Part of the C code looks like this define Mag c c gt x c gt x c y c y bool complex_abs_eq Complex a Complex b double amag Mag a bmag Mag b return amag bmag Note that we will only show the equality operator in this text The other four operators are very similar Refer to complex c or complex source for the details We ma
6. al_bundy gt SELECT FROM shoelace arrive arr name arr quant s13 10 sl6 20 s18 20 3 rows is exactly what s on the part list We take a quick look at the current data al bundy SELECT FROM shoelace sl name sl avail sl color sl len sl unit sl len cm n ES sll 5 black 80 cm 80 s12 6 black 100 cm 100 s17 6 brown 60 cm 60 s13 O black 35 inch 88 9 sl4 8 black 40 inch 101 6 s18 1 brown 40 inch 101 6 s15 4 brown 1 m 100 sl6 0 brown 0 9 m 90 8 rows move the arrived shoelaces in al bundy INSERT INTO shoelace ok SELECT FROM shoelace arrive and check the results al bundy SELECT FROM shoelace ORDER BY sl name sl name sl avail sl color sl len sl unit sl len cm sll 5 black 80 cm 80 12 6 black 100 cm 100 17 6 brown 60 cm 60 14 8 black 40 inch 101 6 s13 10 black 35 inch 88 9 s18 21 brown 40 inch 101 6 s15 4 brown 1 m 100 233 Chapter 13 The Rule System sl6 20 brown 0 9 m 90 8 rows al bundy SELECT FROM shoelace 1og sl name sl availllog who log when 17 6 A1 Tue Oct 20 19 14 45 1998 MET DST 13 10 Al Tue Oct 20 19 25 16 1998 MET DST 16 20 A1 Tue Oct 20 19 25 16 1998 MET DST 18 21 Al Tue Oct 20 19 25 16 1998 MET DST 4 rows It s a long way from the one INSERT SELECT to these results And its descrip
7. 54 pg on connection loss Name pg on connection loss set or change a callback for unexpected connection loss Synopsis pg on connection loss dbHandle callbackCommand Inputs dbHandle Specifies a valid database handle callbackCommand If present provides the command string to execute when connection loss is detected Outputs None Description pg on connection loss creates changes or cancels a request to execute a callback command if an unexpected loss of connection to the database occurs With a ca11backCommand parameter the request is established or the command string of an already existing request is replaced With no ca11backCom mand parameter a prior request is canceled The callback command string is executed from the Tcl idle loop That is the normal idle state of an application written with Tk In non Tk Tcl shells you can execute update or vwait to cause the idle loop to be entered 55 pg lo creat Name pg lo creat create a large object Synopsis pg lo creat conn mode Inputs conn Specifies a valid database connection mode Specifies the access mode for the large object Outputs objOid The OID of the large object created Description pg 1o creat creates an Inversion Large Object Usage mode can be any or ing together of INV READ and INV WRITE The or operator is pg lo creat conn INV READ INV WRITE pg lo open Name pg 1o
8. CREATE TABLE testl i int4 d real p polygon INSERT INTO testl values 1 3 567 polygon 3 0 4 0 1 0 2 0 INSERT INTO testl values 2 89 05 polygon 4 0 3 0 2 0 1 0 28 the expected output is 1 g 2 po 2 tuple 0 got i 4 bytes bytes 2 points boundbox 1 000000 2 000000 tuple 1 89 050003 p 4 bytes hi 4 000000 3 000000 lo 5 include lt stdio h gt include libpq fe h include utils geo decls h void exit nicely PGconn conn POfinish conn exit 1 main char pghost pgport pgoptions pgtty char dbName int nFields int RM j int i_fnum d_fnum p_fnum PGconn Conn PGresult res begin parameters are null defaul using hardwired constants S pghost NULL pgport NULL pgoptions NULL pgtty NULL dbName getenv USER make a connection to the ts by looking up environment variables or Chapter 1 libpq C Library d 4 bytes 3 567000 p 4 hi 3 000000 4 000000 lo ot i 4 bytes 2 d 4 bytes ints boundbox 000000 1 000000 for the POLYGON type by setting the parameters for a backend connection if the then the system will try to use reasonable failing that host name of the backend server port of the backend server Special options to start up the backend server rver de
9. PQtrace conn debug start a transaction block res PQexec conn BEGIN if res PQresultStatus res PGRES COMMAND OK fprintf stderr BEGIN command failed n POclear res exit nicely conn should PQclear PGresult whenever it is no longer needed to avoid memory leaks ae PQclear res fetch rows from the pg_database the system catalog of databases nid res PQexec conn DECLARE mycursor CURSOR FOR SELECT FROM pg database if res PQresultStatus res PGRES COMMAND OK fprintf stderr DECLARE CURSOR command failed n PQclear res exit nicely conn PQclear res res PQexec conn FETCH ALL in mycursor if res PQresultStatus res PGRES TUPLES OK fprintf stderr FETCH ALL command didn t return tuples properly n PQclear res exit nicely conn first print out the attribute names nFields POnfields res for i 0 i lt nFields i printf 15s POfname res i printf n n 25 Chapter 1 libpq C Library next print out the rows for i 0 i lt PQntuples res i for j 0 J lt nFields j printf 15s POQgetvalue res i j printf An PQclear res close the cursor res PQexec conn CLOSE mycursor POclear res commit the transaction res PQexec c
10. eee a E nennen nennen nennen nennen nne 291 viii SPI moditytuple ungneuee pen ERREUR 202 SPEI pall G iie ti et rere ta de eerie dpt polt 294 SPL repalloGcz erste ek Rs HE e nem utei 295 SPI PITE ciss en a Na A EA E a A a a R 296 SPI freetuples since ala RR ie lal nai eae 297 ulum 298 SPI freeplam eee ORE eite nap auos 299 17 4 Visibility of Data Changes ipiri s 300 173 Examples enc ERREUR ERE BERE EE IRE ces eden ERE ERREUR Fre AEN 300 III Procedural Languages eere esee sees ee eee eee ense neta ena staat ts etae tasto setas ease ss tetto sens ense tosta stesse te soa 303 18 Procedural Languages RR PERRO ge ii eee ie cee 305 I8 T Entrodu ction sitet ae HE CHERRRMSER RUE RREF HER ERR 305 18 2 Installing Procedural Languages eeesseeeeseeeeeee eene enne 305 19 PL pgSQL SQL Procedural Language eeeseseeeeeeeeeer eren 307 19 T OVERVIEW iet eren gi dette PEG RR SEEN cet a re e v ER EE er tenets 307 19 1 1 Advantages of Using PL pgSQL esent 308 19 1411 Better Perkormanice i e cette ee ett teer Het heit 308 19 1 1 2 8 QI Support cte erret ee rhe ertet 308 19 4 1 3 Portability eng ereRDROee S nen quse Red OT 308 19 1 2 Developing 1n PL pgSQL 5 ete eem eee reete 309 19 2 Structure of PI pgSQL oerte A ie reete cae hd wees 309 19 2 T Lexica Det lls
11. CREATE TABLE phone data person text phone text private bool CREATE VIEW phone number AS SELECT person phone FROM phone data WHERE NOT private GRANT SELECT ON phone number TO secretary Nobody except him and the database superusers can access the phone data table But due to the GRANT the secretary can SELECT from the phone number view The rule system will rewrite the SELECT from phone number into a SELECT from phone data and add the qualification that only entries where pri vate is false are wanted Since the user is the owner of phone number the read access to phone data is now checked against his permissions and the query is considered granted The check for accessing phone number is also performed but this is done against the invoking user so nobody but the user and the secretary can use it The permissions are checked rule by rule So the secretary is for now the only one who can see the public phone numbers But the secretary can setup another view and grant access to that to public Then anyone can see the phone number data through the secretaries view What the secretary cannot do is to create a view that directly accesses phone data actually he can but it will not work since every access aborts the transaction during the permission checks And as soon as the user will notice that the secretary opened his phone number view he can REVOKE his access Immediately any access
12. occurrence of string2 If n is negative search backwards If m is not passed assume 1 search starts at first character by Roberto Mello rmelloGfslc usu edu modified by Robert Gaszewski graszew poland com Licensed under the GPL v2 or later CREATE FUNCTION instr VARCHAR VARCHAR RETURNS INTEGER AS DECLARE pos integer BEGIN pos instr 1 2 1 RETURN pos D LANGUAGE plpgsql amp 342 Chapter 19 PL pgSQL SQL Procedural Language CREATE FUNCTION instr VARCHAR VARCHAR INTEGER RETURNS INTEGER AS DECLAR string ALIAS FOR 1 string to search ALIAS FOR 2 beg index ALIAS FOR 3 pos integer NOT NULL DEFAULT 0 temp str VARCHAR beg INTEGER length INTEGER Ss length INTEGER IF beg index gt 0 THEN temp str substring string FROM beg index pos position string to search IN temp str IF pos 0 THEN RETURN 0 SE RETURN pos beg index 1 END IF LSE Ss length char length string to search length char length string beg length beg index ss length 2 WHILE beg gt 0 LOOP temp str substring string FROM beg FOR ss length pos position string to search IN temp str IF pos 0 THEN RETURN beg END IF beg beg 1 D LOOP ETURN 0 END I
13. Merge Join gt Seq Scan gt Sort Seq Scan on s gt Seq Scan Sort Seq Scan on shoelace arrive Seq Scan on shoelace data while omitting the extra range table entry would result in a Merge Join gt Seq Scan Sort gt Seq Scan on s gt Seq Scan gt Sort Seq Scan on shoelace arrive that totally produces the same entries in the log relation Thus the rule system caused one extra scan on the shoelace data relation that is absolutely not necessary And the same obsolete scan is done once more in the UPDATE But it was a really hard job to make that all possible at all A final demonstration of the PostgreSQL rule system and its power There is a cute blonde that sells shoelaces And what AI could never realize she s not only cute she s smart too a little too smart Thus it happens from time to time that Al orders shoelaces that are absolutely not sellable This time he ordered 1000 pairs of magenta shoelaces and since another kind is currently not available but he committed to buy some he also prepared his database for pink ones al bundy INSERT INTO shoelace VALUES al bundy sl9 Qj Spink 35 0 inch 0 0 al bundy INSERT INTO shoelace VALUES al bundy 7s110 1000 magenta 40 0 inch 0 0 Since this happens often we must lookup for shoelace entries that fit for absolutely no shoe sometimes We could do that in a complicated statement eve
14. Quantity here is 80 END RAISE NOTICE Quantity here is quantity Quantity here is 50 RETURN quantity LANGUAGE plpgsql It is important not to confuse the use of BEGIN END for grouping statements in PL pgSQL with the database commands for transaction control PL pgSQL s BEGIN END are only for grouping they do not start or end a transaction Functions and trigger procedures are always executed within a transaction established by an outer query they cannot start or commit transactions since PostgreSQL does not have nested transactions 19 2 1 Lexical Details Each statement and declaration within a block is terminated by a semicolon All keywords and identifiers can be written in mixed upper and lower case Identifiers are implicitly converted to lower case unless double quoted There are two types of comments in PL pgSQL A double dash starts a comment that extends to the end of the line A starts a block comment that extends to the next occurrence of Block comments cannot be nested but double dash comments can be enclosed into a block comment and a double dash can hide the block comment delimiters and 310 Chapter 19 PL pgSQL SQL Procedural Language 19 3 Declarations All variables rows and records used in a block must be declared in the declarations section of the block The only exception is that the loop variable of a FOR loop iterating over a range of intege
15. Anything you did at all differently from the installation instructions The PostgreSQL version You can run the command SELECT version to find out the version of the server you are connected to Most executable programs also support a version option at least postmaster version and psql version should work If the function or the options do not exist then your version is more than old enough to warrant an upgrade You can also look into the README file in the source directory or at the name of your distribution file or package name If you run a prepackaged version such as RPMs say so including any subversion the package may have If you are talking about a CVS snapshot mention that including its date and time If your version is older than 7 3 2 we will almost certainly tell you to upgrade There are tons of bug fixes in each new release that is why we make new releases Platform information This includes the kernel name and version C library processor memory infor mation In most cases it is sufficient to report the vendor and version but do not assume everyone knows what exactly Debian contains or that everyone runs on Pentiums If you have installation problems then information about compilers make etc is also necessary Do not be afraid if your bug report becomes rather lengthy That is a fact of life It is better to report everything the first time than us having to squeeze the fac
16. CREATE TABLE shoelace log sl name char 10 shoelace changed 228 Chapter 13 The Rule System Sl avail integer new available value log who text who did it log when timestamp when i CREATE RULE log_shoelace AS ON UPDATE TO shoelace_data WHERE EW sl avail OLD sl_avail DO INSERT INTO shoelace_log VALUES EW sl_name EW sl_avail current_user current_timestamp Now AI does al bundy UPDATE shoelace data SET sl avail 6 al bundy WHERE sl name sl7 and we look at the log table al bundy SELECT FROM shoelace 1og sl name sl availllog who log when s17 6 A1l Tue Oct 20 16 14 45 1998 MET DST 1 row That s what we expected What happened in the background is the following The parser created the parse tree this time the parts of the original parse tree are highlighted because the base of operations is the rule action for update rules UPDATE shoelace data SET sl avail 6 FROM shoelace data shoelace data WHERE bpchareq shoelace data sl name s17 There is a rule log_shoelace that is ON UPDATE with the rule qualification expression int4ne NEW sl avail OLD sl avail and one action INSERT INTO shoelace log VALUES NEW sl name NEW sl avail current user current timestamp FROM shoelace data NEW shoelace data OLD This is a little strange looking
17. Index Scan using comp hostidx on computer The other possible query is a DELETE FROM computer WHERE hostname old with the execution plan Nestloop Index Scan using comp hostidx on computer Index Scan using soft hostidx on software This shows that the planner does not realize that the qualification for the hostname on computer could also be used for an index scan on software when there are multiple qualification expressions combined with AND what he does in the regexp version of the query The trigger will get invoked once for any of the 2000 old computers that have to be deleted and that will result in one index scan over computer and 2000 index scans for the software The rule implementation will do it with two queries over indexes And it depends on the overall size of the software table if the rule will still be faster in the sequential scan 240 Chapter 13 The Rule System situation 2000 query executions over the SPI manager take some time even if all the index blocks to look them up will soon appear in the cache The last query we look at is a DELETE FROM computer WHERE manufacurer bim Again this could result in many rows to be deleted from computer So the trigger will again fire many queries into the executor But the rule plan will again be the nested loop over two index scans Only using another index on computer Nestloop Index Scan using c
18. WHERE proname LIKE bytea The dblink function executes a remote query see cont rib dblink lIt is declared to return record since it might be used for any kind of query The actual column set must be specified in the calling query so that the parser knows for example what should expand to 203 Chapter 9 Extending SQL Functions 9 8 Procedural Language Handlers All calls to functions that are written in a language other than the current version 1 interface for compiled languages this includes functions in user defined procedural languages functions written in SQL and functions using the version 0 compiled language interface go through a call handler function for the specific language It is the responsibility of the call handler to execute the function in a meaningful way such as by interpreting the supplied source text This section describes how a language call handler can be written This is not a common task in fact it has only been done a handful of times in the history of PostgreSQL but the topic naturally belongs in this chapter and the material might give some insight into the extensible nature of the PostgreSQL system The call handler for a procedural language is a normal function which must be written in a com piled language such as C and registered with PostgreSQL as taking no arguments and returning the 1an guage handler type This special pseudo type identifies the handler as a call han
19. CREATE RIGGER tafter AFTER INSERT OR UPDATE OR DELETE ON ttest FOR EACH ROW EXECUTE PROCEDURE trigf CREATE vac INSERT INTO ttest VALUES NULL WARNING trigf fired before there are 0 tuples in ttest INSERT 0 0 Insertion skipped and AFTER trigger is not fired vac SELECT FROM ttest x 0 rows vac INSERT INTO ttest VALUES 1 INFO trigf fired before there are 0 tuples in ttest INFO trigf fired after there are 1 tuples in ttest A AA AA A A remember what we said about visibility INSERT 167793 1 vac SELECT FROM ttest 1 row vac INSERT INTO ttest SELECT x 2 FROM ttest INFO trigf fired before there are 1 tuples in ttest INFO trigf fired after there are 2 tuples in ttest AA A A A remember what we said about visibility INSERT 167794 1 vac SELECT FROM ttest vac gt UPDATE ttest SET x NULL WHERE x 2 INFO trigf fired before there are 2 tuples in ttest vac gt UPDATE ttest SET x 4 WHERE x 2 INFO trigf fired before there are 2 tuples in ttest INFO trigf fired after there are 2 tuples in ttest vac SELECT FROM ttest 256 Chapter 16 Triggers 2 rows vac DELETE FROM ttest INFO trigf fired before there are 2 tuples in tt
20. IF OT FOUND THEN RETURN false END IF RETURN true END LANGUAGE plpgsql 19 3 5 RENAME RENAME oldname TO newname Using the RENAME declaration you can change the name of a variable record or row This is primarily useful if NEW or OLD should be referenced by another name inside a trigger procedure See also ALIAS Examples RENAME id TO user id RENAME this var TO that var Note RENAME appears to be broken as of PostgreSQL 7 3 Fixing this is of low priority since ALIAS covers most of the practical uses of RENAME 19 4 Expressions All expressions used in PL pgSQL statements are processed using the server s regular SQL executor Expressions that appear to contain constants may in fact require run time evaluation e g now for the timestamp type so it is impossible for the PL pgSQL parser to identify real constant values other than the NULL keyword All expressions are evaluated internally by executing a query SELECT expression using the SPI manager In the expression occurrences of PL pgSQL variable identifiers are replaced by parameters and the actual values from the variables are passed to the executor in the parameter array 314 Chapter 19 PL pgSQL SQL Procedural Language This allows the query plan for the SELECT to be prepared just once and then re used for subsequent evaluations The evaluation done by the PostgreSQL main parser ha
21. destination 186 void VARDATA t VARSIZE t VARHDRSZ return new t Chapter 9 Extending SQL Functions source how many bytes text concat_text text argl text arg2 int32 new text size VARSIZE argl VARSIZE arg2 VARHDRSZ text new text text palloc new text size VARATT SIZEP new text new text size memcpy VARDATA new text VARDATA argl VARSIZE argl VARHDRSZ memcpy VARDATA new text VARSIZE argl VARHDRSZ VARDATA arg2 VARSIZE arg2 VARHDRSZ return new text Supposing that the above code has been prepared in file funcs c and compiled into a shared object we could define the functions to PostgreSQL with commands like this CREATE FUNCTION add one int4 RETURNS int4 AS PGROOT tutorial funcs LANGUAGE C WITH isStrict note overloading of SQL function name add one CREATE FUNCTION add one float8 RETURNS float8 AS PGROOT tutorial funcs add one float8 LANGUAGE C WITH isStrict CREATE FUNCTION makepoint point point RETURNS point AS PGROOT tutorial funcs LANGUAGE C WITH isStrict CREATE FUNCTION copytext text RETURNS text AS PGROOT tutorial funcs LANGUAGE C WITH isStrict CREATE FUNCTION concat text text text RETURNS text AS PGROOT tutorial funcs LANGUAGE C WITH isStrict Here PGROOT stands
22. public PGpoint points The points defining this path Constructors public PGpath PGpoint points boolean open Parameters points the PGpoints that define the path 97 Chapter 5 JDBC Interface open True if the path is open false if closed public PGpath Required by the driver public PGpath String s throws SQLException Parameters S definition of the path in PostgreSQL s syntax Throws SQLException on conversion failure Methods public void setValue String s throws SQLException Parameters S Definition of the path in PostgreSQL s syntax Throws SQLException on conversion failure Overrides setValue in class PGobject public boolean equals Object obj Parameters obj Object to compare with Returns true if the two pathes are identical Overrides equals in class PGobject public Object clone This must be overridden to allow the object to be cloned Overrides clone in class PGobject public String getValue This returns the path in the syntax expected by PostgreSQL Overrides getValue in class PGobject 98 public boolean isOpen This returns true if the path is open public boolean isClosed This returns true if the path is closed public void closePath Marks the path as closed public void openPath Marks the path as open Class org postgresql geometric PGpoint java lang Object l t org postgresql util PGobject t org postgresql geometric PGpoint Ch
23. then re 2 more You will turn re probably only need that fer If you were using a rer keys referrer typ rmm end Iss 19 11 2 Porting Functions Example 19 5 A Simple Function Here is an Oracle function CREATE OR REPLAC E FUNCTION cs fmt browser version v name IN varchar v version IN var char RETURN varchar IS BEGI IF v version D IF SHOW ERRORS IS NULL THEN RETURN v name RETURN v name v version Let s go through this function and see the differences to PL pgSQL PostgreSQL does not have named parameters You have to explicitly alias them inside your function Oracle can have IN OUT and INOUT parameters passed to functions The INOUT for example means that the parameter will receive a value and return another PostgreSQL only has IN parameters and functions can return only a single value The RETURN Key word in the function prototype not the function body becomes RETURNS in Post greSQL On PostgreSQL functions are created using single quotes as delimiters so you have to escape single quotes inside your functions which can be quite annoying at times see Section 19 11 1 1 The show errors command does not exist in PostgreSQL So let s see how this function would look when ported to PostgreSQL CREATE OR REPLAC E FUNCTION cs fmt browser version VARCHAR VARCHAR 335 Ch
24. version 1 calling con vention is indicated by writing a PG FUNCTION INFO V1 macro call for the function as illustrated below Lack of such a macro indicates an old style version 0 function The language name specified in CREATE FUNCTION is C in either case Old style functions are now deprecated because of portability problems and lack of functionality but they are still supported for compatibility reasons 9 5 1 Dynamic Loading The first time a user defined function in a particular loadable object file is called in a backend session the dynamic loader loads that object file into memory so that the function can be called The CREATE FUNCTION for a user defined C function must therefore specify two pieces of information for the function the name of the loadable object file and the C name link symbol of the specific function to call within that object file If the C name is not explicitly specified then it is assumed to be the same as the SQL function name The following algorithm is used to locate the shared object file based on the name given in the CREATE FUNCTION command 1 If the name is an absolute path the given file is loaded 2 If the name starts with the string 1ibdir that part is replaced by the PostgreSQL package library directory name which is determined at build time 3 If the name does not contain a directory part the file is searched for in the path specified by the
25. 1 gt 2 return 1 return 2 LANGUAGE pltcl WITH isStrict Note the clause WITH isStrict which saves us from having to think about NULL input values if a NULL is passed the function will not be called at all but will just return a NULL result automatically In a non strict function if the actual value of an argument is NULL the corresponding n variable will be set to an empty string To detect whether a particular argument is NULL use the function argisnull For example suppose that we wanted tc1 max with one null and one non null argument to return the non null argument rather than NULL CREATE FUNCTION tcl max integer integer RETURNS integer AS if argisnull 1 if argisnull 2 return null return 2 if argisnull 2 return 1 if 1 gt 2 return 1 return 2 LANGUAGE pltcl As shown above to return a NULL value from a PL Tcl function execute return null This can be done whether the function is strict or not Composite type arguments are passed to the procedure as Tcl arrays The element names of the array are the attribute names of the composite type If an attribute in the passed row has the NULL value it will not appear in the array Here is an example that defines the overpaid_2 function as found in the older PostgreSQL documentation in PL Tcl CREATE FUNCTION overpaid 2 EMP RETURNS bool AS if 200000 0 lt 1 salary ret
26. 7 empty char sqlext 8 sqlca Many of the empty fields may be used in a future release If no error occurred in the last SQL statement sqica sqlcode will be 0 ECPG NO ERROR If sqlca sqlcode is less that zero this is a serious error like the database definition does not match the query If it is greater than zero it is a normal error like the table did not contain the requested row sqlca sqlerrm sqlerrmc will contain a string that describes the error The string ends with the line number in the source file These are the errors that can occur 12 Out of memory in line d Should not normally occur This indicates your virtual memory is exhausted 200 ECPG UNSUPPORTED Unsupported type s on line d Should not normally occur This indicates the preprocessor has generated something that the library does not know about Perhaps you are running incompatible versions of the preprocessor and the library 70 Chapter 4 ECPG Embedded SQL in C 201 ECPG TOO MANY ARGUMENTS Too many arguments line d This means that the server has returned more arguments than we have matching variables Perhaps you have forgotten a couple of the host variables in the INTO var1 var2 list 202 ECPG TOO FEW ARGUMENTS Too few arguments line d This means that the server has returned fewer arguments than we have host variables Perhaps you have too many host variables in the INTO vari
27. GetAttributeByName is the PostgreSQL system function that returns attributes out of the current row It has three arguments the argument of type TupleTableSlot passed into the function the name of the 191 Chapter 9 Extending SQL Functions desired attribute and a return parameter that tells whether the attribute is null GetAtt ribut eByName re turns a Datum value that you can convert to the proper data type by using the appropriate Dat umGet XXX macro The following command lets PostgreSQL know about the c overpaid function CREATE FUNCTION c overpaid emp int4 RETURNS bool AS PGROOT tutorial funcs LANGUAGE C E 9 5 6 Table Function API The Table Function API assists in the creation of user defined C language table functions Section 9 7 Table functions are functions that produce a set of rows made up of either base scalar data types or composite multi column data types The API is split into two main components support for returning composite data types and support for returning multiple rows set returning functions or SRFs The Table Function API relies on macros and functions to suppress most of the complexity of building composite data types and returning multiple results A table function must follow the version 1 calling convention described above In addition the source file must include include funcapi h 9 5 6 1 Returning Rows Composite Types The Table Function API
28. List of Figures 7 1 How a connection is established ees eesceseecseceececeneecsecesceceeesseceacecsecesaeceaceseeesaeeeneesseecaeeeaeenees 168 8 1 The major PostgreSQL system catalogs eene nene enen nennen 172 List of Examples 1 1 hibpg Example Program 1 retener eterne tente Per E eet Ree eoe deren e ERE Een 24 1 2 hbpq Example Program 2 5 ete re ett en ree Pei ten eec ens 26 1 3 libpq Example Program 3 sees enne nennen enin E treten enne nnr ene 28 2 1 Large Objects with Libpq Example Program essere eene enne 35 3 1 pgtcl Example Program iecore ep eterne ect eer de V TE Ede e NoE Eaa ett ERS 41 5 1 Processing a Simple Query in JDBC sss eene nennen nennen en entente 80 5 2 Simple Delete Example nte e e ripe dere e pt eerte eme eet 81 3 3 Drop Table Example B eer tate e redet bt Ue Edere ite 82 5 4 Binary Data Ex mples eiue eere perterritus e tete RE eer entere ets 83 5 5 Connect ionPoolDataSource Configuration Example seen 109 5 6 DataSource Code Example ee eie ter pe Tert hepar tree eet et onn 110 2 7 DbataSoureeJNDI Code Exampl 5 RE UE E RR egets 111 18 1 Manual Installation of PL pgSQL esses enne nennen retener eene 306 19 1 A PL pgSQL Trigger Procedure Example seen 331 19 2 A Simple PL pgSQL Function to Increment an Integer 332 19 3 A Simple PL pgSQL Function
29. ins IF a posl 0 THEN RETURN Return a blank END IF a pos2 instr v url a posl 2 IF a pos2 0 THEN v host substr v url v path RETURN v host D IF a posl 2 s host substr v url ETURN v host a posl 2 4 zy T LANGUAGE plpgsql R a pos2 a posl1 2 ETURNS VARCHAR AS Note PostgreSQL does not have an instr function so you can work around it using a combination of other functions got tired of doing this and created my own instr functions that behave exactly like Oracle s it makes life easier See the Section 19 11 6 for the code 338 Chapter 19 PL pgSQL SQL Procedural Language 19 11 3 Procedures Oracle procedures give a little more flexibility to the developer because nothing needs to be explicitly returned but it can be through the use of INOUT or OUT parameters An example CREATE OR REPLACE PROCEDURE cs create job v job id IN INTEGER IS a running job count INTEGER PRAGMA AUTONOMOUS TRANSACTION 0 BEGIN LOCK TABLE cs jobs IN EXCLUSIVE MODE 6 SELECT count INTO a running job count FROM cs jobs WHERE end stamp IS NULL IF a running job count 0 THEN COMMIT free lock raise application error 20000 Unable to create a new job a job is cur rently running END
30. tions are executed inside the database server the TRUSTED flag should only be given for languages that do not allow access to database server internals or the file system The languages PL pgSQL PL Tcl PL Perl and PL Python are known to be trusted the languages PL TcIU and PL PerlU are designed to provide unlimited functionality should not be marked trusted In a default PostgreSQL installation the handler for the PL pgSQL language is built and installed into the library directory If Tcl Tk support is configured in the handlers for PL Tcl and PL TclU are also built and installed in the same location Likewise the PL Perl and PL PerlU handlers are built and installed if Perl support is configured and PL Python is installed if Python support is configured The createlang script automates step 2 and step 3 described above Example 18 1 Manual Installation of PL pgSQL The following command tells the database server where to find the shared object for the PL pgSQL lan guage s call handler function CREATE FUNCTION plpgsql call handler RETURNS LANGUAGE HANDLER AS libdir plpgsql LANGUAGE C The command CREATE TRUSTED PROCEDURAL LANGUAGE plpgsql HANDLER plpgsql call handler then defines that the previously declared call handler function should be invoked for functions and trigger procedures where the language attribute is plpgsql 306 Chapter 19 PL pgSQL SQL
31. to wait for backend data to arrive thereby using no CPU power unless there is something to do See POsocket to obtain the file de scriptor number to use with select Note that this will work OK whether you submit queries with PQsendQuery PQgetResult or simply use PQexec You should however remember to check PQno tifies after each POgetResult or PQexec to see if any notifications came in during the processing of the query 1 7 Functions Associated with the COPY Command The COPY command in PostgreSQL has options to read from or write to the network connection used by libpq Therefore functions are necessary to access this network connection directly so applications may take advantage of this capability 17 Chapter 1 libpq C Library These functions should be executed only after obtaining a PGRES COPY OUT or PGRES COPY IN result object from PQexec or POgetResult PQgetline Reads a newline terminated line of characters transmitted by the backend server into a buffer string of size length int PQgetline PGconn conn char string int length Like fgets this routine copies up to length 1 characters into string It is like get s however in that it converts the terminating newline into a zero byte POget1ine returns EOF at the end of input 0 if the entire line has been read and 1 if the buffer is full but the terminating newline has not yet been read Notice that the application must check to see
32. 100 Chapter 5 JDBC Interface Translate the point with the supplied amount Parameters x integer amount to add on the x axis y integer amount to add on the y axis public void translate double x double y Translate the point with the supplied amount Parameters x double amount to add on the x axis y double amount to add on the y axis public void move int x int y Moves the point to the supplied coordinates Parameters x integer coordinate y integer coordinate public void move double x double y Moves the point to the supplied coordinates Parameters x double coordinate y double coordinate public void setLocation int x int y Moves the point to the supplied coordinates java awt Point for description of this Parameters x integer coordinate y integer coordinate See Also Point public void setLocation Point p refer to Moves the point to the supplied java awt Point refer to java awt Point for description of this Parameters p Point to move to 101 Chapter 5 JDBC Interface See Also Point Class org postgresql geometric PGpolygon java lang Object l t org postgresql util PGobject org postgresql geometric PGpolygon public class PGpolygon extends PGobject implements Serializable Cloneable This implements the polygon data type within PostgreSQL Variables public PGpoint points The points defining the polygon Constructors publi
33. Ee 2 EN sll 5 black 80 cm 80 s12 6 black 100 cm 100 s17 7 brown 60 cm 60 s13 O black 35 inch 88 9 sl4 8 black 40 inch 101 6 s18 1 brown 40 inch 101 6 s15 4 brown 1 m 100 sl6 0 brown 0 9 m 90 8 rows It s the simplest SELECT Al can do on our views so we take this to explain the basics of view rules The S EL CT FROM shoelace Was interpreted by the parser and produced the parse tree SEI shoelace ECT shoelace sl_col shoelace sl_uni sl_name or t FROM shoelace shoela ce shoelace sl_avail shoelace sl_len shoelace sl len cm 222 Chapter 13 The Rule System and this is given to the rule system The rule system walks through the range table and checks if there are rules in pg rewrite for any relation When processing the range table entry for shoelace the only one up to now it finds the RETURN rule with the parse tree SELECT s sl name s sl avail S sl color s sl len s sl unit float8mul s sl len u un fact AS sl len cm FROM shoelace OLD shoelace NEW shoelace data s unit u WHERE bpchareq s sl unit u un name Note that the parser changed the calculation and qualification into calls to the appropriate functions But in fact this changes nothing To expand the view the rewriter simply creates a subselect range table entry containing the rule s action parse tree and substitutes this range table entry for the original one that referenced t
34. If the function returns a composite type the result columns get the same names as the individual attributes of the type A table function may be aliased in the FRoM clause but it also may be left unaliased If a function is used in the FROM clause with no alias the function name is used as the relation name Table functions work wherever tables do in SELECT statements For example CREATE TABLE foo fooid int foosubid int fooname text CREATE FUNCTION getfoo int RETURNS setof foo AS SELECT FROM foo WHERE fooid 1 LANGUAGE SQL SELECT FROM getfoo 1 AS t1 SELECT FROM foo HERE foosubid in select foosubid from getfoo foo fooid z where z fooid foo fooid CREATE VIEW vw getfoo AS SELECT FROM getfoo 1 SELECT FROM vw getfoo are all valid statements In some cases it is useful to define table functions that can return different column sets depending on how they are invoked To support this the table function can be declared as returning the pseudo type record When such a function is used in a query the expected row structure must be specified in the query itself so that the system can know how to parse and plan the query Consider this example SE ECT FROM dblink dbname templatel select proname prosrc from pg proc AS tl proname name prosrc text
35. It could also happen that we tell you to update to a newer version to see if the bug happens there Or we might decide that the bug cannot be fixed before some major rewrite we might be planning is done Or perhaps it is simply too hard and there are more important things on the agenda If you need help immediately consider obtaining a commercial support contract 6 1 Identifying Bugs Before you report a bug please read and re read the documentation to verify that you can really do whatever it is you are trying If it is not clear from the documentation whether you can do something or not please report that too it is a bug in the documentation If it turns out that the program does something different from what the documentation says that is a bug That might include but is not limited to the following circumstances A program terminates with a fatal signal or an operating system error message that would point to a problem in the program A counterexample might be a disk full message since you have to fix that yourself A program produces the wrong output for any given input A program refuses to accept valid input as defined in the documentation A program accepts invalid input without a notice or error message But keep in mind that your idea of invalid input might be our idea of an extension or compatibility with traditional practice PostgreSQL fails to compile build or install according to the instructions on su
36. The fd argument must have been returned by a previous lo open The number of bytes actually read is returned In the event of an error the return value is negative 2 3 7 Seeking on a Large Object To change the current read or write location on a large object call int lo lseek PGconn conn int fd int offset int whence This routine moves the current location pointer for the large object described by d to the new location specified by offset The valid values for whence are SEEK SET SEEK CUR and SEEK END 2 3 8 Closing a Large Object Descriptor A large object may be closed by calling int lo close PGconn conn int fd where d is a large object descriptor returned by 1o open On success 1o close returns zero On error the return value is negative 34 Chapter 2 Large Objects 2 3 9 Removing a Large Object To remove a large object from the database call int lo unlink PGconn conn Oid lobjId The 20b jId argument specifies the OID of the large object to remove In the event of an error the return value is negative 2 4 Server side Built in Functions There are two built in registered functions 1o import and lo export which are convenient for use in SQL queries Here is an example of their use CREATE TABLE image name text raster oid INSERT INTO imag name raster VALUES beautiful image lo_import etc motd SELE
37. They generally correspond to what are often known as abstract data types PostgreSQL can only operate on such types through methods provided by the user and only understands the behavior of such types to the extent that the user describes them Composite types are created whenever the user creates a table PostgreSQL stores these types in only one way within the file that stores all rows of a table but the user can look inside at the attributes of these types from the query language and optimize their retrieval by for example defining indexes on the attributes PostgreSQL base types are further divided into built in types and user defined types Built in types like int4 are those that are compiled into the system User defined types are those created by the user in the manner to be described later 171 Chapter 8 Extending SQL An Overview 8 3 About the PostgreSQL System Catalogs Having introduced the basic extensibility concepts we can now take a look at how the catalogs are actually laid out You can skip this section for now but some later sections will be incomprehensible without the information given here so mark this page for later reference All system catalogs have names that begin with pg The following tables contain information that may be useful to the end user There are many other system catalogs but there should rarely be a reason to query them directly Table 8 1 PostgreSQL System Catalogs Catalog
38. black This parse tree will surely insert three new log entries And that s absolutely correct Here we can see why it is important that the original parse tree is executed last If the UPDATE would have been executed first all the rows are already set to zero so the logging INSERT would not find any row where 0 shoelace data sl avail 231 Chapter 13 The Rule System 13 4 3 Cooperation with Views A simple way to protect view relations from the mentioned possibility that someone can try to INSERT UPDATE and DELETE on them is to let those parse trees get thrown away We create the rules CREATE RULE shoe ins protect AS ON INSERT TO shoe DO INSTEAD NOTHING CREATE RULE shoe upd protect AS ON UPDATE TO shoe DO INSTEAD NOTHING CREATE RULE shoe del protect AS ON DELETE TO shoe DO INSTEAD NOTHING I If Al now tries to do any of these operations on the view relation shoe the rule system will apply the rules Since the rules have no actions and are INSTEAD the resulting list of parse trees will be empty and the whole query will become nothing because there is nothing left to be optimized or executed after the rule system is done with it A more sophisticated way to use the rule system is to create rules that rewrite the parse tree into one that does the right operation on the real tables To do that on the shoelace view we create the following
39. d The database returned a numeric value and the variable was not numeric 244 ECPG VAR NOT CHAR Variable is not a character type in line d The database returned a non numeric value and the variable was numeric 400 ECPG PGSQL Postgres error s line d Some PostgreSQL error The message contains the error message from the PostgreSQL backend 401 ECPG TRANS Error in transaction processing line d PostgreSQL signaled that we cannot start commit or rollback the transaction 402 ECPG CONNECT Could not connect to database s in line d The connect to the database did not work nd ce e ECPG NOT FOUND Data not found line d This is a normal error that tells you that what you are querying cannot be found or you are at the end of the cursor 4 7 Including Files To include an external file into your embedded SQL program use EXEC SQL INCLUDE filename The embedded SQL preprocessor will look for a file named i1ename h preprocess it and include it in the resulting C output Thus embedded SQL statements in the included file are handled correctly Note that this is not the same as include lt filename h gt 72 Chapter 4 ECPG Embedded SQL in C because the file would not be subject to SOL command preprocessing Naturally you can continue to use the C include directive to include other header files Note The include file name is case sens
40. rs null while rs next open the large object for reading int oid rs getInt 1 84 Chapter 5 JDBC Interface LargeObject obj lobj open oid LargeObjectManager READ xead the data byte buf new byte obj size obj read buf 0 obj size do something with the data read here Close the object obj close rs close ps close 5 7 PostgreSQL Extensions to the JDBC API PostgreSQL is an extensible database system You can add your own functions to the backend which can then be called from queries or even add your own data types As these are facilities unique to PostgreSQL we support them from Java with a set of extension API s Some features within the core of the standard driver actually use these extensions to implement Large Objects etc 5 7 1 Accessing the Extensions To access some of the extensions you need to use some extra methods in the org postgresql PGConnection class In this case you would need to case the return value of Driver getConnection For example Connection db Driver getConnection url username password later on Fastpath fp org postgresql PGConnection db getFastpathAPI 5 7 1 1 Class org postgresql PGConnection public class PGConnection These are the extra methods used to gain access to PostgreSQL s extensions 5 7 1 1 1 Methods public Fastpath getFastpathAPI throws SQLException This re
41. sults are stored into Tcl variables remaining rows if any are ignored No store occurs if the SELECT returns no rows this case can be detected by checking the result of spi exec For example spi exec SELECT count AS cnt FROM pg proc will set the Tcl variable cnt to the number of rows in the pg proc system catalog 347 Chapter 20 PL Tcl Tcl Procedural Language If the optional 1oop body argument is given it is a piece of Tcl script that is executed once for each row in the SELECT result note 200p body is ignored if the given query is not a SELECT The values of the current row s fields are stored into Tcl variables before each iteration For example Spi exec array C SELECT FROM pg class elog DEBUG have table C relname will print a DEBUG log message for every row of pg class This feature works similarly to other Tcl looping constructs in particular continue and break work in the usual way inside the loop body If a field of a SELECT result is NULL the target variable for it is unset rather than being set spi prepare query typelist Prepares and saves a query plan for later execution The saved plan will be retained for the life of the current backend The query may use arguments which are placeholders for values to be supplied whenever the plan is actually executed In the query string refer to arguments by the symbols 1 n If the query uses arguments the nam
42. the connection is ready Either of these states should be equally detectable from the return value of POconnectPoll as above Other states may be shown during and only during an asynchronous connection procedure These indicate the current stage of the connection procedure and may be useful to provide feedback to the user for example These statuses may include CONNECTION STARTED Waiting for connection to be made CONNECTION MADE Connection OK waiting to send CONNECTION AWAITING RESPONSE Waiting for a response from the server CONNECTION AUTH OK Received authentication waiting for connection start up to continue CONNECTION SETENV Negotiating environment part of the connection start up Note that although these constants will remain in order to maintain compatibility an application should never rely upon these appearing in a particular order or at all or on the status always being one of these documented values An application may do something like this switch PQstatus conn case CONNECTION_STARTED feedback Connecting break case CONNECTION_MADE feedback Connected to server break default dback Connecting Chapter 1 libpq C Library Note that if POconnectStart returns a non NULL pointer you must call POfinish when you are finished with it in order to
43. 3 PG GETARG INT32 1 build a tuple tuple BuildTupleFromCStrings attinmeta values make the tuple into a datum result TupleGetDatum slot tuple Clean up this is not actually necessary pfree values 0 pfree values 1 pfree values 2 pfree values SREF RETURN NEXT funcctx result else do when there is no more left SRF RETURN DONE funcctx with supporting SQL code of CREATE TYPE __testpassbyval AS fl int4 f2 int4 f3 int4 CREATE OR REPLACE FUNCTION testpassbyval int4 int4 RETURNS setof X testpassbyval AS MODULE PATHNAME testpassbyval LANGUAGE c IMMUTABLE STRICT See cont rib tablefunc for more examples of table functions 9 5 7 Writing Code We now turn to the more difficult task of writing programming language functions Be warned this section of the manual will not make you a programmer You must have a good understanding of C including the use of pointers before trying to write C functions for use with PostgreSQL While it may be possible to load functions written in languages other than C into PostgreSQL this is often difficult when it is possible at all because other languages such as FORTRAN and Pascal often do not follow the same calling convention as C That is other languages do not pass argument and return values between functions in the same way For this reason we will assu
44. 3 4 Attributes Using the TYPE and ROWTYPE attributes you can declare variables with the same data type or structure as another database item e g a table field variable TYPE STYPE provides the data type of a variable or database column You can use this to declare variables that will hold database values For example let s say you have a column named user id in your users table To declare a variable with the same data type as users user id you write user id users user id TYPE By using TYPE you don t need to know the data type of the structure you are referencing and most important if the data type of the referenced item changes in the future e g you change your table definition of user id from INTEGER to REAL you may not need to change your function definiti table ROWTYPE ion SROWTYPE provides the composite data type corresponding to a whole row of the specified table table must be an existing table or view name of the database DECLARE users rec users ROWTYPE user id users user id TYPE BEGIN user id users rec user id 313 Chapter 19 PL pgSQL SQL Procedural Language CREATE FUNCTION does view exist INTEGER RETURNS bool AS DECLARE key ALIAS FOR 1 table data cs materialized views ROWTYPE Em BEGIN SELECT INTO table data FROM cs materialized views WHERE sort key key
45. C strings to produce a properly formed tuple The metadata is stored here to avoid redundant work across multiple calls To return a tuple you must create a tuple slot based on the TupleDesc You can use TupleTableSlot TupleDescGetSlot TupleDesc tupdesc to initialize this tuple slot or obtain one through other user provided means The tuple slot is needed to create a Datum for return by the function The same slot can and should be re used on each call After constructing an Att InMetadata structure HeapTuple BuildTupleFromCStrings AttInMetadata attinmeta char values can be used to build a HeapTupl1e given user data in C string form values is an array of C strings one for each attribute of the return tuple Each C string should be in the form expected by the input function of the attribute data type In order to return a null value for one of the attributes the corresponding pointer in the values array should be set to NULL This function will need to be called again for each tuple you return Building a tuple via TupleDescGetAtt InMetadata and BuildTupleFromCStrings is only conve nient if your function naturally computes the values to be returned as text strings If your code naturally computes the values as a set of Datums you should instead use the underlying heap ormtuple routine to convert the Dat ums directly into a tuple You will still need the TupleDesc and a TupleTableSlot but not Att InMetadata Once you have
46. Currently binary tuple data can only be returned by a query that extracts data from a binary cursor 1 3 5 Retrieving SELECT Result Values PQgetvalue Returns a single field column value of one tuple row of a PGresult Tuple and field indices start at 0 char POgetvalue const PGresult res int tup num int field num For most queries the value returned by POget value is a null terminated character string representation of the attribute value But if PObinaryTuples is 1 the value returned by PQget value is the binary representation of the type in the internal format of the backend server but not including the size word if the field is variable length It is then the programmer s responsibility to cast and convert the data to the correct C type The pointer returned by PQget value points to storage that is part of the PGresult structure One should not modify it and one must explicitly copy the value into other storage if it is to be used past the lifetime of the PGresult structure itself POgetisnull Tests a field for a NULL entry Tuple and field indices start at 0 int POgetisnull const PGresult res ll Chapter 1 libpq C Library int tup num int field num This function returns 1 if the field contains a NULL 0 if it contains a non null value Note that Poget value will return an empty string not a null pointer for a NULL field PQgetlength Returns the length of a field attribute value in bytes
47. Extending SQL Operators 11 3 2 NEGATOR The NEGATOR clause if provided names an operator that is the negator of the operator being defined We say that operator A is the negator of operator B if both return Boolean results and x A y equals NOT x B y for all possible inputs x y Notice that B is also the negator of A For example lt and gt are a negator pair for most data types An operator can never validly be its own negator Unlike commutators a pair of unary operators could validly be marked as each others negators that would mean A x equals NOT B x for all x or the equivalent for right unary operators An operator s negator must have the same left and or right operand types as the operator itself so just as with COMMUTATOR only the operator name need be given in the NEGATOR clause Providing a negator is very helpful to the query optimizer since it allows expressions like NOT x y to be simplified into x lt gt y This comes up more often than you might think because NOT operations can be inserted as a consequence of other rearrangements Pairs of negator operators can be defined using the same methods explained above for commutator pairs 11 3 3 RESTRICT The RESTRICT clause if provided names a restriction selectivity estimation function for the operator note that this is a function name not an operator name RESTRICT clauses only make sense for binary operators that return boolean The idea behin
48. IF DELETE FROM cs active job INSERT INTO cs active job job id VALUES v job i3 BEGI INSERT INTO cs jobs job id start stamp VALUES v job id sysdate EXCEPTION WHEN dup val on index THEN NULL don t worry if it al ready exists END COMMIT END show errors Procedures like this can be easily converted into PostgreSQL functions returning an INTEGER This pro cedure in particular is interesting because it can teach us some things Q There is no pragma statement in PostgreSQL O If youdoa LOCK TABLE in PL pgSQL the lock will not be released until the calling transaction is finished You also cannot have transactions in PL pgSQL procedures The entire function and other functions called from therein is executed in a transaction and PostgreSQL rolls back the results if something goes wrong Therefore only one BEGIN statement is allowed O Theexception when would have to be replaced by an IF statement So let s see one of the ways we could port this procedure to PL pgSQL 339 Chapter 19 PL pgSQL SQL Procedural Language CREATE OR REPLACE FUNCTION cs create job INTEGER RETURNS INTEGER AS DECLARE v job id ALIAS FOR 1 a running job count INTEGER a num INTEGER PRAGMA AUTONOMOUS TRANSACTION BEGIN LOCK TABLE cs
49. Lear ge Objects esee Ote DOqaneg medie 103 5 7 3 1 Class org postgresql largeobject LargeOb ject e s 103 5 7 3 1 Variables etes onGheoes eee nee 104 57 3 12 Methods a onc caet e he eie etes 104 5 7 3 2 Class org postgresql largeobject LargeObjectManager 105 5 31 3 2 T Variables 5 peso ete e URIERR EIS 106 5 7 3 2 2 Methods 5 sb unneesesesetotemeeseeso neret 106 5 8 Using the driver in a multithreaded or a servlet environment sess 107 5 9 Connection Pools And DataSources sesssseseseeeeee eene eee nre 107 5 9 1 JDBC JDK Version Support eene ener 107 5 9 2 JDBC Connection Pooling API sess 107 5 9 3 Application Servers ConnectionPoolDataSource eee 108 5 9 4 Applications DataSource esesssseeeseeeeeeee eene eene nennen 109 5 9 5 DataSources and JNDI tette edere erp dein 111 5 9 6 Specific Application Server Configurations esee 112 5 10 Further Reading eere ei Ate ta iq i Ede tite quce 112 6 PyGreSQL Python Interface eese trennen eren en nennen nenne A enne 113 6 T The pg Module t eret de eie ice eet edet 113 6 1 L Constants ced uei a ei a eta a ee HIE ee 113 6 2 pg Module Functions creck snwcod chev erect e e a Los iet ite pete lens 114 CODDeGCL cope Siok eRe AE EE EE AAEE E 114 BOT CEMMOS rrer e NEO TETEE EE 117 set dethost EE E
50. Name Description lg database databases pg class tables log attribute table columns pg index indexes 3 proc procedures functions lg type data types both base and complex log operator operators log aggregate aggregate functions Ig am access methods Ipg amop access method operators Ipg amproc access method support functions Ig opclass access method operator classes 172 Chapter 8 Extending SQL An Overview Figure 8 1 The major PostgreSQL system catalogs p ttre lid j RLRE typinput typoutput typrecelve typsend D N Pg am lj 1 laid o amgettuple nminsert amdelete am zetattr Z 173 KEY ambeginsean AITITES Cag Chapter 8 Extending SQL An Overview The Developer s Guide gives a more detailed explanation of these catalogs and their columns However Figure 8 1 shows the major entities and their relationships in the system catalogs Columns that do not refer to other entities are not shown unless they are part of a primary key This diagram is more or less incomprehensible until you actually start looking at the contents of the catalogs and see how they relate to each other For now the main things to take away from this diagram are as follows In several of the sections that follow we will present various join queries on the system catalogs that display information we need to extend the system Looking at this diagram s
51. PGREALM is set PostgreSQL applications will attempt authentication with servers for this realm and use separate ticket files to avoid conflicts with local ticket files This environment variable is only used if Kerberos authentication is selected by the backend PGOPTIONS sets additional run time options for the PostgreSQL backend PGTTY sets the file or tty on which debugging messages from the backend server are displayed PGREQUIRESSL sets whether or not the connection must be made over SSL If set to 1 libpq will refuse to connect if the server does not accept an SSL connection This option is only available if PostgreSQL is compiled with SSL support PGCONNECT TIMEOUT sets the maximum number of seconds that libpq will wait when attempting to connect to the PostgreSQL server This option should be set to at least 2 seconds The following environment variables can be used to specify user level default behavior for every Post greSQL session PGDATESTY Ec E sets the default style of date time representation PGTZ sets the default time zone PGCLIENTENCODING sets the default client encoding if multibyte support was selected when config uring PostgreSQL The following environment variables can be used to specify default internal behavior for every Post greSQL session PGGEQO sets the default mode for the genetic optimizer Refer to the SET S
52. PGresult res If the SQL command that generated the PGresult was INSERT UPDATE or DELETE this returns a string containing the number of rows affected If the command was anything else it returns the empty string 12 Chapter 1 libpq C Library PQoidValue Returns the object ID of the inserted row if the SOL command was an INSERT that inserted exactly one row into a table that has OIDs Otherwise returns InvalidOid Oid PQoidValue const PGresult res The type oid and the constant InvalidOid will be defined if you include the libpq header file They will both be some integer type PQoidStatus Returns a string with the object ID of the inserted row if the SOL command was an INSERT The string will be 0 if the INSERT did not insert exactly one row or if the target table does not have OIDs If the command was not an INSERT returns an empty string char PQoidStatus const PGresult res This function is deprecated in favor of PQoidValue and is not thread safe 1 4 Asynchronous Query Processing The PQexec function is adequate for submitting commands in simple synchronous applications It has a couple of major deficiencies however PQexec waits for the command to be completed The application may have other work to do such as maintaining a user interface in which case it won t want to block waiting for the response Since control is buried inside PQexec it is hard for the frontend to decide it would like to
53. PQsetnonblocking should not use select until POflush has returned 0 indicating that there is no buffered data waiting to be sent to the backend A typical frontend using these functions will have a main loop that uses select to wait for all the con ditions that it must respond to One of the conditions will be input available from the backend which in select s terms is readable data on the file descriptor identified by POQsocket When the main loop detects input ready it should call PoconsumeInput to read the input It can then call PQisBusy fol lowed by PQgetResult if PQisBusy returns false 0 It can also call POonotifies to detect NOTIFY messages see Section 1 6 A frontend that uses PQsendQuery PQgetResult can also attempt to cancel a command that is still being processed by the backend PQrequestCancel Request that PostgreSQL abandon processing of the current command int PQrequestCancel PGconn conn The return value is 1 if the cancel request was successfully dispatched 0 if not If not PoerrorMes sage tells why not Successful dispatch is no guarantee that the request will have any effect however Regardless of the return value of POQrequestCancel the application must continue with the normal result reading sequence using POget Result If the cancellation is effective the current command will terminate early and return an error result If the cancellation fails say because the backend was already done processing the
54. SPI OK FINISH if properly disconnected SPI ERROR UNCONNECTED if called from an un connected procedure Description SPI finish closes an existing connection to the SPI manager You must call this function after complet ing the SPI operations needed during your procedure s current invocation You may get the error return SPI ERROR UNCONNECTED if SPI finish is called without having a current valid connection There is no fundamental problem with this it means that nothing was done by the SPI manager Usage SPI finish must be called as a final step by a connected procedure or you may get unpredictable results However you do not need to worry about making this happen if the transaction is aborted via elog ERROR In that case SPI will clean itself up Algorithm SPI finish performs the following Disconnects your procedure from the SPI manager and frees all memory allocations made by your procedure via palloc since the SPI connect These allocations can t be used any more See Memory management 262 SPI exec Name SPI exec Creates an execution plan parser planner optimizer and executes a query Synopsis SPI exec query tcount Inputs char query String containing query plan int tcount Maximum number of tuples to return Outputs int SPI ERROR UNCONNECTED if called from an un connected procedure SPI ERROR ARGUMENT if query is NULL or tcount lt 0 SPI ERROR UNCONNECTED if procedure is unconnected S
55. SQL Note that statement level trigger events are not supported in the current version You can currently specify BEFORE or AFTER on INSERT DELETE or UPDATE of a tuple as a trigger event 16 1 Trigger Definition If a trigger event occurs the trigger manager called by the Executor sets up a TriggerData information structure described below and calls the trigger function to handle the event The trigger function must be defined before the trigger itself can be created The trigger function must be declared as a function taking no arguments and returning type t rigger The trigger function receives its input through a TriggerData structure not in the form of ordinary function arguments If the function is written in C it must use the version 1 function manager interface The syntax for creating triggers is CREATE TRIGGER trigger BEFORE AFTER INSERT DELETE UPDATE OR ON relation FOR EACH ROW STATEMENT EXECUTE PROCEDURE procedure args where the arguments are trigger The trigger must have a name distinct from all other triggers on the same table The name is needed if you ever have to delete the trigger BEFORE AFTER Determines whether the function is called before or after the event INSERT DELETE UPDATE The next element of the command determines what event s will trigger the function Multiple event
56. THEN RETURN beg END IF END IF beg beg 1 END LOOP RETURN 0 END IF END LANGUAGE plpgsql 344 Chapter 20 PL Tcl Tcl Procedural Language PL Tcl is a loadable procedural language for the PostgreSQL database system that enables the Tcl lan guage to be used to write functions and trigger procedures This package was originally written by Jan Wieck 20 1 Overview PL Tcl offers most of the capabilities a function writer has in the C language except for some restrictions The good restriction is that everything is executed in a safe Tcl interpreter In addition to the limited command set of safe Tcl only a few commands are available to access the database via SPI and to raise messages via elog There is no way to access internals of the database backend or to gain OS level access under the permissions of the PostgreSQL user ID as a C function can do Thus any unprivileged database user may be permitted to use this language The other implementation restriction is that Tcl procedures cannot be used to create input output functions for new data types Sometimes it is desirable to write Tcl functions that are not restricted to safe Tcl for example one might want a Tcl function that sends mail To handle these cases there is a variant of PL Tcl called PL TclU for untrusted Tcl This is the exact same language except that a full Tcl interpreter is used If PL TclU is used it must be installed as an untruste
57. Trigger Manager This section describes the low level details of the interface to a trigger function This information is only needed when writing a trigger function in C If you are using a higher level function language then these details are handled for you 253 Chapter 16 Triggers Note The interface described here applies for PostgreSQL 7 1 and later Earlier versions passed the TriggerData pointer in a global variable currentTriggerData When a function is called by the trigger manager it is not passed any normal parameters but it is passed a context pointer pointing to a TriggerData structure C functions can check whether they were called from the trigger manager or not by executing the macro CALLED AS TRIGGER fcinfo which expands to fcinfo context NULL amp amp IsA fcinfo context TriggerData If this returns true then it is safe to cast fcinfo gt context to type TriggerData and make use of the pointed to TriggerData structure The function must not alter the TriggerData structure or any of the data it points to struct TriggerData is defined in commands trigger h typedef struct TriggerData odeTag type TriggerEvent tg event Relation tg relation HeapTuple tg trigtuple HeapTuple tg newtuple Trigger tg trigger TriggerData where the members are defined as follows type Always T TriggerData if this is a trigger event tg event describes the event for which th
58. Tuple and field indices start at 0 int POgetlength const PGresult res int tup num int field num This is the actual data length for the particular data value that is the size of the object pointed to by POgetvalue Note that for character represented values this size has little to do with the binary size reported by POfsize PQprint Prints out all the tuples and optionally the attribute names to the specified output stream void PQprint FILE fout output stream const PGresult res const PQprintOpt po struct pqbool header print output field headings and row count pqbool align fill align the fields pqdbool standard old brain dead format pqbool html3 output html tables pqbool expanded expand tables pqbool pager use pager for output if needed char fieldSep field separator char tableOpt insert to HTML table char caption HTML caption char fieldName null terminated array of replacement field names PQprintOpt This function was formerly used by psql to print query results but this is no longer the case and this function is no longer actively supported 1 3 6 Retrieving Non SELECT Result Information PQcmdStatus Returns the command status string from the SQL command that generated the PGre sult char PQcmdStatus PGresult res PQcmdTuples Returns the number of rows affected by the SQL command char PQcmdTuples
59. UPDATE and he knows that this result should go into table t1 But which of the rows that are there has to be replaced by the new row To resolve this problem another entry is added to the target list in UPDATE and also in DELETE statements the current tuple ID CTID This is a system attribute containing the file block number and position in the block for the row Knowing the table the CTID can be used to retrieve the original t1 row to be updated After adding the CTID to the target list the query actually looks like SELECT tl a t2 b tl ctid FROM tl t2 WHERE tl a t2 a Now another detail of PostgreSQL enters the stage At this moment table rows aren t overwritten and this is why ABORT TRANSACTION is fast In an UPDATE the new result row is inserted into the table after stripping CTID and in the tuple header of the row that CTID pointed to the cmax and xmax entries are set to the current command counter and current transaction ID Thus the old row is hidden and after the transaction committed the vacuum cleaner can really move it out Knowing all that we can simply apply view rules in absolutely the same way to any command There is no difference 13 3 4 The Power of Views in PostgreSQL The above demonstrates how the rule system incorporates view definitions into the original parse tree In the second example a simple SELECT from one view created a final parse tree that is a join of 4 tables unit is use
60. attribute eg oid then the appropriate negative attribute number will be returned The caller should be careful to test for exact equality to SPI ERROR NOATTRIBUTE to detect error testing for result lt 0 is not correct unless system attributes should be rejected 279 SPI fname Name SPI fname Finds the attribute name for the specified attribute number Synopsis SPI fname tupdesc fnumber Inputs TupleDesc tupdesc Input tuple description int fnumber Attribute number Outputs char Attribute name NULL if fnumber is out of range SPI result set to SPI ERROR NOATTRIBUTE on error Description SPI fname returns the attribute name for the specified attribute Usage Attribute numbers are 1 based Algorithm Returns a newly allocated copy of the attribute name Use pfree to release the copy when done with it 280 SPI getvalue Name SPI getvalue Returns the string value of the specified attribute Synopsis SPI getvalue tuple tupdesc fnumber Inputs HeapTuple tuple Input tuple to be examined TupleDesc tupdesc Input tuple description int fnumber Attribute number Outputs char Attribute value or NULL if attribute is NULL fnumber is out of range SPI result set to SPI ERROR NOATTRIBUTE no output function available SPI result set to SPI ERROR NOOUTFUNC Description SPI getvalue returns an external string representation of the value of the specified attribu
61. bottommost selects will be pulled up into the middle select since there s no need to process them separately But the middle select will remain separate from the top because it contains aggregate functions If we pulled those up it would change the behavior of the topmost select which we don t want However collapsing the query tree is an optimization that the rewrite system doesn t have to concern itself with Note There is currently no recursion stopping mechanism for view rules in the rule system only for the other kinds of rules This doesn t hurt much because the only way to push this into an endless loop blowing up the backend until it reaches the memory limit is to create tables and then setup the view rules by hand with CREATE RULE in such a way that one selects from the other that selects from the one This could never happen if CREATE VIEW is used because for the first CREATE VIEW the second relation does not exist and thus the first view cannot select from the second 13 3 3 View Rules in Non SELECT Statements Two details of the parse tree aren t touched in the description of view rules above These are the command type and the result relation In fact view rules don t need this information There are only a few differences between a parse tree for a SELECT and one for any other command Obviously they have another command type and this time the result relation points to the range table entry where the result should go Every
62. buf int Oft int len throws SQL Exception Reads some data from the object into an existing array Parameters buf destination array off offset within array 104 Chapter 5 JDBC Interface len number of bytes to read public void write byte buf throws SQLException Writes an array to the object public void write byte buf int off int len throws SQLException Writes some data from an array to the object Parameters buf destination array off offset within array len number of bytes to write 5 7 3 2 Class orzg postgresql largeobject LargeObjectManager public class LargeObjectManager extends Object java lang Object l t org postgresql largeobject LargeObjectManager This class implements the large object interface to PostgreSQL It provides methods that allow client code to create open and delete large objects from the database When opening an object an instance of org postgresql largeobject LargeObject is returned and its methods then allow access to the object This class can only be created by org postgresql PGConnection To get access to this class use the fol lowing segment of code import org postgresql largeobject Connection conn LargeObjectManager 10bj 105 Chapter 5 JDBC Interface code that opens a connection lobj org postgresql PGConnection myconn getLargeObjectAPI Normally client code would use the BLOB methods to access lar
63. by the original parse tree INSERT INTO shoelace log VALUES NEW sl name NEW sl avail current user current timestamp FROM shoelace data NEW shoelace data OLD shoelace data shoelace data WHERE int4ne NEW sl avail OLD sl avail AND bpchareq shoelace data sl name s17 Step 4 replaces NEW references by the target list entries from the original parse tree or by the matching variable references from the result relation INSERT INTO shoelace log VALUES shoelace data sl name 6 current user current timestamp FROM shoelace data NEW shoelace data OLD shoelace data shoelace data WHERE int4ne 6 OLD sl avail AND bpchareq shoelace data sl name s17 Step 5 changes OLD references into result relation references INSERT INTO shoelace log VALUES shoelace data sl name 6 current user current timestamp FROM shoelace data NEW shoelace data OLD shoelace data shoelace data WHERE int4ne 6 shoelace data sl avail AND bpchareq shoelace data sl name s17 230 Chapter 13 The Rule System That s it Since the rule is not INSTEAD we also output the original parse tree In short the output from the rule system is a list of two parse trees that are the same as the statements INSERT TO shoelace log VALUES hoelace data sl name 60 urrent user current timestamp WHERE AND l shoelace data sl avail Ab S
64. call this the data dictionary The catalogs appear to the user as tables like any other but the DBMS stores its internal bookkeeping in them One key difference between PostgreSQL and standard relational systems is that PostgreSQL stores much more information in its catalogs not only information about tables and columns but also information about its types func tions access methods and so on These tables can be modified by the user and since PostgreSQL bases its internal operation on these tables this means that PostgreSQL can be extended by users By comparison conventional database systems can only be extended by changing hardcoded procedures within the DBMS or by loading modules specially written by the DBMS vendor PostgreSQL is also unlike most other data managers in that the server can incorporate user written code into itself through dynamic loading That is the user can specify an object code file e g a shared library that implements a new type or function and PostgreSQL will load it as required Code written in SQL is even more trivial to add to the server This ability to modify its operation on the fly makes PostgreSQL uniquely suited for rapid prototyping of new applications and storage structures 8 2 The PostgreSQL Type System The PostgreSQL type system can be broken down in several ways Types are divided into base types and composite types Base types are those like int4 that are implemented in a language such as C
65. can be downloaded from the PostgreSQL JDBC web site Alternatively you can build the driver from source but you should only need to do this if you are making changes to the source code For details refer to the PostgreSQL installation instructions After installation the driver should be found in PREFIX share java postgresql jar The resulting driver will be built for the version of Java you are running If you build with a 1 1 JDK you will build a version that supports the JDBC 1 specification if you build with a Java 2 JDK e g JDK 1 2 or JDK 1 3 you will build a version that supports the JDBC 2 specification 5 1 2 Setting up the Class Path To use the driver the JAR archive named postgresql jar if you built from source otherwise it will likely be named 3dbc7 2 1 1 3jaror jdbc7 2 1 2 jar for the JDBC 1 and JDBC 2 versions respec tively needs to be included in the class path either by putting it in the CLASSPATH environment variable or by using flags on the java command line For instance I have an application that uses the JDBC driver to access a large database containing astro nomical objects I have the application and the JDBC driver installed in the usr local 1lib directory and the Java JDK installed in usr 10ca1 jdk1 3 1 To run the application I would use export CLASSPATH usr local lib finder jarO usr local pgsql share java postgresql jar java Finder Q finder jar contains the Finder application l htt
66. checks for valid values are required and in the case of an invalid value an error message should be generated it must be done by a trigger for now On the other hand a trigger that is fired on INSERT on a view can do the same as a rule put the data somewhere else and suppress the insert in the view But it cannot do the same thing on UPDATE or DELETE because there is no real data in the view relation that could be scanned and thus the trigger would never get called Only a rule will help For the things that can be implemented by both it depends on the usage of the database which is the best A trigger is fired for any row affected once A rule manipulates the parse tree or generates an additional one So if many rows are affected in one statement a rule issuing one extra query would usually do a better job than a trigger that is called for any single row and must execute his operations this many times For example There are two tables CREATE TABLE computer hostname text indexed manufacturer text indexed CREATE TABLE software software text indexed hostname text indexed i Both tables have many thousands of rows and the index on hostname is unique The hostname column contains the full qualified domain name of the computer The rule trigger should constraint delete rows from software that reference the deleted host Since the trigger is called for each individual row deleted from
67. command then there will be no visible result at all 15 Chapter 1 libpq C Library Note that if the current command is part of a transaction cancellation will abort the whole transaction POrequestCancel can safely be invoked from a signal handler So it is also possible to use it in con junction with plain PQexec if the decision to cancel can be made in a signal handler For example psql invokes PQrequestCancel from a SIGINT signal handler thus allowing interactive cancellation of queries that it issues through PQexec Note that PQrequestCancel will have no effect if the connection is not currently open or the backend is not currently processing a command 1 5 The Fast Path Interface PostgreSQL provides a fast path interface to send function calls to the backend This is a trapdoor into system internals and can be a potential security hole Most users will not need this feature PQfn Request execution of a backend function via the fast path interface PGresult PQfn PGconn conn int fnid int result buf int result len int result is int const PQArgBlock args int nargs The fnid argument is the object identifier of the function to be executed result buf is the buffer in which to place the return value The caller must have allocated sufficient space to store the return value there is no check The actual result length will be returned in the integer pointed to by re sult len If a 4 byte integer result is exp
68. command allows more They can have no action They can have multiple actions The keyword INSTEAD is optional The pseudo relations NEW and OLD become useful They can have rule qualifications Second they don t modify the parse tree in place Instead they create zero or many new parse trees and can throw away the original one 13 4 2 How These Rules Work Keep the syntax CREATE RULE rule name AS ON event TO object WHERE rule qualification DO INSTEAD action actions NOTHING in mind In the following update rules means rules that are defined ON INSERT UPDATE or DELETE Update rules get applied by the rule system when the result relation and the command type of a parse tree are equal to the object and event given in the CREATE RULE command For update rules the rule system creates a list of parse trees Initially the parse tree list is empty There can be zero NOTHING keyword one or multiple actions To simplify we look at a rule with one action This rule can have a qualification or not and it can be INSTEAD or not What is a rule qualification It is a restriction that tells when the actions of the rule should be done and when not This qualification can only reference the NEW and or OLD pseudo relations which are basically the relation given as object but with a special meaning So we have four cases that produce the following parse trees for a one action rule 227 Chapter
69. configuration variable dynamic library path 4 Otherwise the file was not found in the path or it contains a non absolute directory part the dynamic loader will try to take the name as given which will most likely fail It is unreliable to depend on the current working directory If this sequence does not work the platform specific shared library file name extension often so is appended to the given name and this sequence is tried again If that fails as well the load will fail Note The user ID the PostgreSQL server runs as must be able to traverse the path to the file you intend to load Making the file or a higher level directory not readable and or not executable by the postgres user is a common mistake In any case the file name that is given in the CREATE FUNCTION command is recorded literally in the system catalogs so if the file needs to be loaded again the same procedure is applied Note PostgreSQL will not compile a C function automatically The object file must be compiled before it is referenced in a CREATE FUNCTION command See Section 9 5 8 for additional information 182 Chapter 9 Extending SQL Functions Note After it is used for the first time a dynamically loaded object file is retained in memory Future calls in the same session to the function s in that file will only incur the small overhead of a symbol table lookup If you need to force a reload of an object file for example after recom
70. database row for INSERT UPDATE operations in ROW level triggers OLD Data type RECORD variable holding the old database row for UPDATE DELETE operations in ROW level triggers 330 Chapter 19 PL pgSQL SQL Procedural Language G NAME Data type name variable that contains the name of the trigger actually fired G WHEN Data type text a string of either BEFORE or AFTER depending on the trigger s definition G LEVEL Data type text a string of either ROW or STATEMENT depending on the trigger s definition TG OP Data type text a string of INSERT UPDATE or DELE fired rj E telling for which operation the trigger is G_RELID Data type oid the object ID of the table that caused the trigger invocation G_RELNAME Data type name the name of the table that caused the trigger invocation TG_NARGS Data type integer the number of arguments given to the trigger procedure in the CREATE TRIGGER statement TG ARGV Data type array of text the arguments from the CREATE TRIGGER statement The index counts from 0 and can be given as an expression Invalid indices lt 0 or gt tg nargs result in a null value A trigger function must return either NULL or a record row value having exactly the structure of the table the trigger was fired for Triggers fired BEFORE may return NULL to sig
71. dbname Note Users of source packages must specially enable the build of PL Python during the installation process refer to the installation instructions for more information Users of binary packages might find PL Python in a separate subpackage 22 1 PL Python Functions The Python code you write gets transformed into a function E g CREATE FUNCTION myfunc text RETURNS text AS return args 0 LANGUAGE plpython gets transformed into def plpython procedure myfunc 23456 return args 0 where 23456 is the OID of the function If you do not provide a return value Python returns the default None which may or may not be what you want The language module translates Python s None into the SQL null value The PostgreSQL function parameters are available in the global args list In the myfunc example args 0 contains whatever was passed in as the text argument For myfunc2 text integer args 0 would contain the text variable and args 1 the integer variable The global dictionary SD is available to store data between function calls This variable is private static data The global dictionary GD is public data available to all Python functions within a session Use with care Each function gets its own restricted execution object in the Python interpreter so that global data and function arguments from myfunc are not available to myfunc2 The exception is the data in the GD dictionary as mentio
72. dictionary with the field names used as the dictionary index 151 listfields Name listfields list the fields names of the query result Synopsis listfields Parameters none Return Type list field names Exceptions SyntaxError Too many arguments pg error Invalid query result or invalid connection Description listfields method returns the list of field names defined for the query result The fields are in the same order as the result values 152 fieldname Name fieldname get field name by number Synopsis fieldname i Parameters field number integer Return Type string field name Exceptions TypeError Bad parameter type or too many arguments ValueError Invalid field number pg error Invalid query result or invalid connection Description fieldname method allows to find a field name from its rank number It can be useful for displaying a result The fields are in the same order than the result values 153 fieldnum Name fieldnum get field number by name Synopsis fieldnum name Parameters name field name string Return Type integer field number integer Exceptions TypeError Bad parameter type or too many arguments ValueError Unknown field name pg error Invalid query result or invalid connection Description fieldnum method returns a field number from its name It can be
73. eie 252 16 2 Interaction with the Trigger Manager sese 253 16 3 Visibility of Data Changes eene ueteres 255 16 4 Examples e tree ceret qe de dus nevis REI wees 256 17 Server Programming Interface toca tte peti plene nt rhe eri En 260 17 1 Interface Functions e ERE ERREUR RI a nants 260 SBLconnectz ote bett beet ehe bre reser iub hut Ee dedi 260 SPIsfinish s icone iae ea Ue a P ede E dei teas 262 RM UE ER EI E ER 263 SPI ptepare bett Une a E S EE EEEE Reb eii E 266 SPI E CCP EEEE dei tou eo p o E ER 268 SPL cursor dm EE 270 SPI cursorzfind 5 Bates hates eos staan edendis ee D2 SPI c rsor fetch uen OU DP EO NEUTER RITE 273 SPL_CUrSOP_MOVE SARA EE E EEEE E E A 274 SPI cursor cloSe iae etie A veo es ee e ti Eee een dte 275 Nul ysgbu E PE eek outa tans 276 17 2 Interface Support Funct ons s sei ceteri Macatee tt dede e to eodem 278 SPI fn mber ierat a e AN UNA 2778 SPE fnafne z annee eased asec tbi ete ban petere ceechietie e bietet oce tore E ble sensed 280 SPL getvalue ERR a e WR Peng 281 dul ioc B 283 SPI gettype sen eh ueber hee ti oR eee ee I E E 285 SPL Petty pers 4 toe be e EE n i E e p ies 286 SPI getreln me i ee eoe er eR ae eee ek ena Pes 287 17 3 Memory Management i teeth tei e d dei eto ero dei 288 SPI COpytuple eene p entupeeeteele i eee ORT 288 SPI copytupled sC e eb eu P ere eei c EE EEE 290 SPI copytupleintoslot
74. emp RETURNS text AS SELECT 1 name LANGUAGE SQL SELECT getname new emp getname one 1 row 9 2 4 SQL Table Functions A table function is one that may be used in the FROM clause of a query All SQL language functions may be used in this manner but it is particularly useful for functions returning composite types If the function is defined to return a base type the table function produces a one column table If the function is defined to return a composite type the table function produces a column for each column of the composite type Here is an example CREATE TABLE foo fooid int foosubid int fooname text INSERT INTO foo VALUES 1 1 Joe INSERT INTO foo VALUES 1 2 Ed INSERT INTO foo VALUES 2 1 Mary CREATE FUNCTION getfoo int RETURNS foo AS SELECT FROM foo WHERE fooid 1 LANGUAGE SQL SELECT upper fooname FROM getfoo 1 AS t1 fooid foosubid fooname upper H H 1 1 Joe JOE 2 rows As the example shows we can work with the columns of the function s result just the same as if they were columns of a regular table Note that we only got one row out of the function This is because we did not say SETOF 179 Chapter 9 Extending SQL Functions 9 2 5 SQL Functions Returning Sets When an SQL function is decla
75. ena be Ue teded edili etos 33 2 3 3 Exporting a Large Object rennen eene 33 2 3 4 Opening an Existing Large Object sese 33 2 3 5 Writing Data to a Large Object nennen 34 2 3 6 Reading Data from a Large Object sse 34 iii 2 3 7 Seeking on a Large Object ener 34 2 3 8 Closing a Large Object Descriptor sseeeeeeeeenen nene 34 2 3 9 Removing a Large Object sseesssessseseeeeeennen enne nnne 34 2 4 Server side Built in Functions eee ene enne trennen 35 2 5 Accessing Large Objects from Libpq ee eee eee csecsseeseceeceeceeeeeeecseesaesaecneceseeeeeeseneeaee 35 3 patel Tel Binding Iabraty oder reet ceteri e Pt tte de 41 3 T Introduction tentent bai cedere eta i ite i aeo honed 41 3 2 Loading pgtcl into your application oo lees ceeceeeeeeecaeessesaeceeceeeeeeeeaeesessaesaeenees 42 3 3 pgtcl Command Reference Information sess 42 Dg CONNECT a serie ter a URDU DE OH ERI RR MERE se Er EGER EE r ER d 43 PEA CISCONMECT o ted tiem et tede cam i eret eee 45 pe conndefaults nott eerie Hp Ep ertet ptite 46 PECK EC PTS 47 PE xesult soos EDU UNES 48 pszselect 5 ine eet eee CO ai e n E etus 50 PE EXECUTE LETT 52 PRANStE Ny tice uomen ee Pie ee QU SERE 54 pe on connection VOSS esses uto ot eph er es et rh ER 55 pg lo ere t i oue eee oe eR P ERE ei EE soba tua Ie terres 56 pelo Open ao
76. export must be used in a BI Example 3 1 shows EGIN COMMIT transaction block a small example of how to use the routines 4l Example 3 1 pgtcl Example Program getDBs d get the names of all the databases at a given host and port number with the defaults being the localhost and port 5432 d return them in alphabetical order proc getDBs host localhost port 5432 datnames is the list to be result set conn pg connect templatel host host port Sport set res pg exec conn SELECT datname FROM pg database ORDER BY datname set ntups pg result Sres numTuples for set i 0 i lt Sntups incr i lappend datnames pg result res getTuple i pg_result Sres clear pg_disconnect conn return Sdatnames 3 2 Loading pgtcl into your application Before using pgtcl commands you must load 1ibpgtc1 into your Tcl application This is normally done with the Tcl load command Here is an example load libpgtcl info sharedlibextension The use of info sharedlibextension is recommended in preference to hard wiring so or s1 into the program The load command will fail unless the system s dynamic loader knows where to look for the libpgtcl shared library file You may need to work with ldconfig or set the environment variable LD_LIBRARY_PATH or use some equivalent facility for your platform to make it work Refer to the PostgreSQL installation instructions for more
77. for i 0 zoo 3 i 30 printf type d Sd size d i POftype res i i POfsize res i for i 0 i POntuples res int ival float dval int plen POLYGON pval Chapter 1 libpq C Library we hard wire this to the 3 fields we know about ival int POQgetvalue res float POQgetvalue res dval plen PQgetlength res i i fnum d fnum plen doesn t include the length field so need to increment by VARHDSZ f pval POLYGON malloc plen VARHDRSZ pval gt size plen memmove char amp pval gt npts printf tuple d got n i printf i d bytes d n PQgetlength res i printf d d bytes f n PQgetlength res i PQgetvalue res i p_fnum plen ival dval printf p d bytes d points tboundbox hi f f lo f f n PQgetlength res i pval npts pval boundbox xh pval boundbox yh pval boundbox xl pval boundbox yl PQclear res close the cursor I res PQexec conn CLOSE mycursor POclear res commit the transaction res PQexec conn COMMIT PQclear res close the connection to the database and POfinish conn return 0 cleanup 3l Chapter 2 Large Objects 2 1 Introduction In PostgreSQL releases prior to 7 1 the size of any row in the database could not exceed the size of a data page Since th
78. has a set of data types that can store geometric features into a table These include single points lines and polygons We support these types in Java with the org postgresql geometric package It contains classes that extend the org postgresql util PGobject class Refer to that class for details on how to implement your own data type handlers Class org postgresql geometric PGbox java lang Object t org postgresql util PGobject t org postgresql geometric PGbox public class PGbox extends PGobject implements Serializable Cloneable This represents the box data type within PostgreSQL Variables public PGpoint point These are the two corner points of the box Constructors public PGbox double x1 double yl double x2 double y2 Parameters xl first x coordinate yl first y coordinate X2 second x coordinate y2 second y coordinate 90 Chapter 5 JDBC Interface public PGbox PGpoint pl PGpoint p2 Parameters pl first point p2 second point public PGbox String s throws SQLException Parameters S Box definition in PostgreSQL syntax Throws SQLException if definition is invalid public PGbox Required constructor Methods public void setValue String value throws SQLException This method sets the value of this object It should be overridden but still called by subclasses Parameters value a string representation of the value of th object Th
79. in SQL queries esses 9 1 3 4 Retrieving SELECT Result Information eee 10 1 3 5 Retrieving SELECT Result Values sees 11 1 3 6 Retrieving Non SELECT Result Information seen 12 1 4 Asynchronous Query Processing teen nennen entente 13 1 5 The Fast Path Interface eere eR CAREER EUER OPERE eS 16 1 6 Asynchronous Notification eeeseseseeeeeeeneee rennen nennen nen renes nennen nnne 16 1 7 Functions Associated with the COPY Command eese 17 1 8 libpq Tracing Functions isione esinsin sno nenne etre entre nee nnne 19 1 9 libpq Control Functions tne teg ete rd ertet pe diitetis 20 1 10 Environment Variables eese eeeeeeeeeeeee enne nennen nennt tenente entente e eene 20 ILI Files iuh tenes Re tee e tes 21 1 12 Threading Behavior osien nren cie teo e pe YR e Pee eb ed 22 1 13 Building Libpq Programs iiiter etre eite terere eb i 22 1 14 Example Programs cists titi mp Un EP ORB ered QE Reps 23 2 large Objects unt benieo ATE og ih tesa altel ces 32 2 Introduction 5er re rere i tusk Pee coe OSEE ER EY RC E aa 32 2 2 Implementation Features eite tette deperire eet erbe debitis 32 2 3 TIntetfaces s oe EFE ER e EE A EEAO urere e RERO SEE E RUE 32 2 3 1 Greating a Large Object ees iestietane geo itueteietgtpegre 33 2 322 Importing a L rge ObjJect Reed
80. inadequate for future data processing applications The relational model successfully replaced previous models in part because of its Spartan simplicity However this simplicity makes the implementation of certain applications very difficult PostgreSQL offers substantial additional power by incorporating the following additional concepts in such a way that users can easily extend the system inheritance data types functions Other features provide additional power and flexibility constraints triggers rules transactional integrity These features put PostgreSQL into the category of databases referred to as object relational Note that this is distinct from those referred to as object oriented which in general are not as well suited to support ing traditional relational database languages So although PostgreSQL has some object oriented features it is firmly in the relational database world In fact some commercial databases have recently incorporated features pioneered by PostgreSQL 1 http s2k ftp CS Berkeley EDU 8000 postgres postgres html Preface 2 A Short History of PostgreSQL The object relational database management system now known as PostgreSQL and briefly called Post gres95 is derived from the POSTGRES package written at the University of California at Berkeley With over a decade of development behind it PostgreSQL is the most advanced open source database available anywhere offering mul
81. information libpgtcl in turn depends on 1ibpq so the dynamic loader must also be able to find the 1ibpq shared library In practice this is seldom an issue since both of these shared libraries are normally stored in the same directory but it can be a stumbling block in some configurations If you use a custom executable for your application you might choose to statically bind 1ibpgtcl into the executable and thereby avoid the load command and the potential problems of dynamic linking See the source code for pgtclsh for an example 42 pg connect 3 3 pgtcl Command Reference Information pg connect Name pg connect open a connection to the backend server Synopsis pg connect conninfo connectOptions pg connect dbName host hostName port portNumber tty pqtty options optionalBackendArgs Inputs new style connectOptions A string of connection options each written in the form keyword value A list of valid options can be found in 1ibpq s PQconnectdb manual entry Inputs old style dbName Specifies a valid database name host hostName Specifies the domain name of the backend server for dbName port portNumber Specifies the IP port number of the backend server for dbName tty pqtty Specifies file or tty for optional debug output from backend options optionalBackendArgs Specifies options for the backend server for dbName 43 pg connect Outputs dbHandle If succe
82. is an integer false for other results args FastpathArguments to pass to fastpath Returns null if no data Integer if an integer result or byte otherwise public Object fastpath String name boolean resulttype FastpathArg args throws SQLException Send a function call to the PostgreSQL backend by name Note The mapping for the procedure name to function id needs to exist usually to an earlier call to addfunction This is the preferred method to call as function id s can may change between versions of the backend For an example of how this works refer to org postgresql LargeObject Parameters name Function name resulttype True if the result is an integer false for other results args FastpathArguments to pass to fastpath Returns null if no data Integer if an integer result or byte otherwise See Also LargeObject public int getInteger String name FastpathArg args throws SQLException 87 Chapter 5 JDBC Interface This convenience method assumes that the return value is an Integer Parameters name Function name args Function arguments Returns integer result Throws SQLException if a database access error occurs or no result public byte getData String name FastpathArg args throws SQLException This convenience method assumes that the return value is binary data Parameters name Function name args Function arguments Returns byte array containing result
83. is planned to equip TOAST with such functionality in the future This section describes the implementation and the programming and query language interfaces to Post greSQL large object data We use the libpq C library for the examples in this section but most program ming interfaces native to PostgreSQL support equivalent functionality Other interfaces may use the large object interface internally to provide generic support for large values This is not described here 2 2 Implementation Features The large object implementation breaks large objects up into chunks and stores the chunks in tuples in the database A B tree index guarantees fast searches for the correct chunk number when doing random access reads and writes 2 3 Interfaces The facilities PostgreSQL provides to access large objects both in the backend as part of user defined functions or the front end as part of an application using the interface are described below For users familiar with POSTGRES 4 2 PostgreSQL has a new set of functions providing a more coherent interface Note All large object manipulation must take place within an SQL transaction This requirement is strictly enforced as of PostgreSQL 6 5 though it has been an implicit requirement in previous versions resulting in misbehavior if ignored 32 Chapter 2 Large Objects The PostgreSQL large object interface is modeled after the Unix file system interface with analogues of open 2 read 2 wri
84. jobs IN EXCLUSIVE MODE SELECT count INTO a running job count FROM cs jobs WHERE end stamp IS NULL IF a running job count gt 0 COMMIT free lock RAISE EXCEPTION Unable to create a new job a job is currently running Er Iw H nj DELETE FROM cs active job INSERT INTO cs active job job id VALUES v job i3 SELECT count into a num FROM cs jobs WHERE job id v job id IF NOT FOUND THEN If nothing was returned in the last query This job is not in the table so lets insert it INSERT INTO cs jobs job id start stamp VALUES v job id sysdate RETURN 1 ELSE RAISE NOTICE Job already running Er e H fr RETURN 0 END LANGUAGE plpgsql Q Notice how you can raise notices or errors in PL pgSQL 19 11 4 Packages Note haven t done much with packages myself so if there are mistakes here please let me know Packages are a way Oracle gives you to encapsulate PL SQL statements and functions into one entity like Java classes where you define methods and objects You can access these objects methods with a dot Here is an example of an Oracle package from ACS 4 the ArsDigita Community System 4 http www arsdigita com doc 340 CR AS EN S h Chapter 19 PL pgSQL SQL Proced
85. ld b o foo sl foo o HP UX uses the extension s1 for shared libraries unlike most other systems IRIX PIC is the default no special compiler options are necessary The linker option to produce shared libraries is shared coe Foose ld shared o foo so foo o Linux The compiler flag to create PIC is fpic On some platforms in some situations fPIC must be used if pic does not work Refer to the GCC manual for more information The compiler flag to create a shared library is shared A complete example looks like this GG fpic o fooec cc shared o foo so foo o MacOS X Here is a sample It assumes the developer tools are installed Coe Eoosc cc bundle flat namespac undefined suppress o foo so foo o 200 Chapter 9 Extending SQL Functions NetBSD The compiler flag to create PIC is pic For ELF systems the compiler with the flag shared is used to link shared libraries On the older non ELF systems 1d Bshareable is used goce fpic c foo c gcc shared o foo so foo o OpenBSD The compiler flag to create PIC is pic 1d Bshareable is used to link shared libraries gcc fpic c foo c ld Bshareable o foo so foo o Solaris The compiler flag to create PIC is KP IC with the Sun compiler and pic with GCC To link shared libraries the compiler option is G with either compiler or alternatively shared with GCC cc KPIC c foo c cc G o foo so foo o or gece fpic c foose gcc
86. mation Systems Vienna University of Technology November 29 1998 Discusses SQL history and syntax and describes the addition of INTERSECT and EXCEPT constructs into PostgreSQL Prepared as a Master s Thesis with the support of O Univ Prof Dr Georg Gottlob and Univ Ass Mag Katrin Seyr at Vienna University of Technology A Yu and J Chen The POSTGRES Group The Postgres95 User Manual University of California Sept 5 1995 Zelaine Fong The design and implementation of the POSTGRES query optimizer University of Califor nia Berkeley Computer Science Department l http s2k ftp CS Berkeley EDU 8000 postgres papers 2 http s2k ftp CS Berkeley EDU 8000 postgres papers UCB MS zfong pdf 359 Bibliography Proceedings and Articles Nels Olson Partial indexing in POSTGRES research project University of California UCB Engin T7 49 1993 O676 1993 L Ong and J Goh A Unified Framework for Version Modeling Using Production Rules in a Database System ERL Technical Memorandum M90 33 University of California April 1990 L Rowe and M Stonebraker The POSTGRES data model Proc VLDB Conference Sept 1987 P Seshadri and A Swami Generalized Partial Indexes Proc Eleventh International Conference on Data Engineering 6 10 March 1995 IEEE Computer Society Press Cat No 95CH35724 1995 p 420 7 M Stonebraker and L Rowe The design of POSTGRES Proc ACM SIGMOD Conferenc
87. nbytes lo write conn lobj_fd buf nwritten len nwritten nwritten nbytes free buf fprintf stderr n lo_close conn lobj_fd exportFile export large object lobjOid to file out filename ay void exportFile PGconn conn Oid lobjId char filename int lobj_fd char buf BUFSIZE int nbytes tmp int fd create an inversion object 5 lobj fd lo open conn lobjId INV READ if 10bj fd 0 fprintf stderr can t open large object d n lobjId open the file to be written to Af fd open filename O_CREAT O_WRONLY 0666 if fd lt 0 error fprintf stderr can t open unix file s n filename read in from the Unix file and write to the inversion file Ef while nbytes lo read conn 1l1obj fd buf BUFSIZE gt 0 tmp write fd buf nbytes if tmp nbytes fprintf stderr error while writing s n 38 Chapter 2 Large Objects filename void lo close conn l1lobj fd void close fd return void exit nicely PGconn conn PQfinish conn exit 1 int main int argc char argv char in_filename out_filename char database Oid lob jOid PGconn conn PGresult res if argc 4 fprintf stderr Usage s database name in filename out_filename n argv 0 exit 1 database argv 1 in_filename argv 2 out filena
88. of a SELECT INTO is mostly identical to a CREATE TABLE INSERT SELECT sequence and is not discussed separately here On INSERT UPDATE and DELETE queries the result relation is the table or view where the changes take effect the target list The target list is a list of expressions that define the result of the query In the case of a SELECT the expressions are what builds the final output of the query They are the expressions between the SELECT and the FROM keywords is just an abbreviation for all the attribute names of a relation It is expanded by the parser into the individual attributes so the rule system never sees it DELETE queries don t need a target list because they don t produce any result In fact the planner will add a special CTID entry to the empty target list But this is after the rule system and will be discussed later For the rule system the target list is empty In INSERT queries the target list describes the new rows that should go into the result relation It is the expressions in the VALUES clause or the ones from the SELECT clause in INSERT SELECT The first step of the rewrite process adds target list entries for any columns that were not assigned to by the original query and have defaults Any remaining columns with neither a given value nor a default will be filled in by the planner with a constant NULL expression In UPDATE queries the target list describes the new rows that should replace the o
89. of a procedural language and the ease of use of SQL but saving lots of time because you don t have the whole client server communication overhead This can make for a considerable performance increase 19 1 1 2 SQL Support PL pgSQL adds the power of a procedural language to the flexibility and ease of SQL With PL pgSQL you can use all the data types columns operators and functions of SQL 308 Chapter 19 PL pgSQL SQL Procedural Language 19 1 1 3 Portability Because PL pgSQL functions run inside PostgreSQL these functions will run on any platform where PostgreSQL runs Thus you can reuse code and reduce development costs 19 1 2 Developing in PL pgSQL Developing in PL pgSQL is pretty straight forward especially if you have developed in other database procedural languages such as Oracle s PL SQL Two good ways of developing in PL pgSQL are Using a text editor and reloading the file with psq1 Using PostgreSQL s GUI Tool PgAccess One good way to develop in PL pgSQL is to simply use the text editor of your choice to create your functions and in another window use psq1 PostgreSQL s interactive monitor to load those functions If you are doing it this way it is a good idea to write the function using CREATE OR REPLACE FUNCTION That way you can reload the file to update the function definition For example CREATE OR REPLACE FUNCTION testfunc INTEGER RETURNS INTEGER AS
90. of the form tupno attributeName assignbyidx arrayName appendstr assign the results to an array using the first attribute s value and the remaining attributes names as keys If appendstr is given then it is appended to each key In short all but the first field of each tuple are stored into the array using subscripts of the form firstFieldValue fieldNameAppendStr 48 pag result getTuple tupleNumber returns the fields of the indicated tuple in a list Tuple numbers start at zero tupleArray tupleNumber arrayName stores the fields of the tuple in array arrayName indexed by field names Tuple numbers start at Zero attributes returns a list of the names of the tuple attributes lAttributes returns a list of sublists name ftype fsize foreach tuple attribute clear clear the result query object Outputs The result depends on the selected option as described above Description pg result returns information about a query result created by a prior pg exec You can keep a query result around for as long as you need it but when you are done with it be sure to free it by executing pg result clear Otherwise you have a memory leak and Pgtcl will eventually start complaining that you ve created too many query result objects 49 pg select Name pg select loop over the result of a SELECT statement Synopsis pg select dbHandle queryString arrayVar queryProcedure Inputs dbHandle S
91. open open a large object Synopsis pg lo open conn objOid mode Inputs conn Specifies a valid database connection objOid Specifies a valid large object OID mode Specifies the access mode for the large object Outputs fd A file descriptor for use in later pg lo routines Description pg 1o open open an Inversion Large Object Usage Mode can be either r w or rw 57 pg lo close Name pg lo close close a large object Synopsis pg lo close conn fd Inputs conn Specifies a valid database connection fd A file descriptor for use in later pg lo routines Outputs None Description pg 1o close closes an Inversion Large Object Usage 58 pg lo read Name pg lo read read a large object Synopsis pg lo read conn fd bufVar len Inputs conn Specifies a valid database connection fd File descriptor for the large object from pg lo open bufVar Specifies a valid buffer variable to contain the large object segment len Specifies the maximum allowable size of the large object segment Outputs None Description pg 1o readreads at most len bytes from a large object into a variable named bufVar Usage bufVar must be a valid variable name 59 pg lo write Name pg lo write write a large object Synopsis pg lo write conn fd buf len Inputs conn Specifies a valid database connection fd File descriptor for the large objec
92. prevent any unwarranted headaches in the future See Also LargeObjectManager public int getID String name throws SQLException 88 Chapter 5 JDBC Interface This returns the function id associated by its name If addFunction or addFunctions have not been called for this name then an SQLException is thrown 5 7 1 3 Class orzg postgresql fastpath FastpathArg public class FastpathArg extends Object java lang Object l t org postgresql fastpath FastpathArg Each fastpath call requires an array of arguments the number and type dependent on the function being called This class implements methods needed to provide this capability For an example on how to use this refer to the org postgresql LargeObject package See Also Fastpath LargeObjectManager LargeObject 5 7 1 3 1 Constructors public FastpathArg int value Constructs an argument that consists of an integer value Parameters value int value to set public FastpathArg byte bytes Constructs an argument that consists of an array of bytes Parameters bytes array to store public FastpathArg byte buf Int off int len Constructs an argument that consists of part of a byte array Parameters buf source array off offset within array 89 Chapter 5 JDBC Interface len length of data to include public FastpathArg String s Constructs an argument that consists of a String 5 7 2 Geometric Data Types PostgreSQL
93. proc RETURNS INTEGER AS DECLARE referrer keys RECORD Declare a generic record to be used in a FOR a output varchar 4000 BEGIN a output CREATE FUNCTION cs find referrer type VARCHAR VARCHAR VARCHAR RETURNS VARCHAR AS DECLARE v host ALIAS FOR 1 336 Chapter 19 PL pgSQL SQL Procedural Language v domain ALIAS FOR 2 v url ALIAS FOR 3 BEGIN Notice how we scan through the results of a query in a FOR loop using the FOR record construct FOR referrer keys IN SELECT FROM cs referrer keys ORDER BY try order LOOP a output a output IF v_ referrer keys kind LIKE referrer keys key string THEN RETURN referrer keys referrer typ pd Pe END IET END LOOP a output a output RETURN NULL END LANGUAGE plpgsql This works because we are not substituting any variables Otherwise it would fail Look at PERFORM for another way to run functions EXECUTE a output END LANGUAGE plpgsql Example 19 7 A Procedure with a lot of String Manipulation and OUT Parameters The following Oracle PL SQL procedure is used to parse a URL and return several elements host path and query It is an procedure because in PL pgSQL functions only one value can be returned see Section 19 11 3 In PostgreSQL one
94. rules CREATE RULE shoelace ins AS ON INSERT TO shoelace DO INSTEAD INSERT INTO shoelace data VALUES Sl name z 3 Sl avail Sl color z sl len Ej Bi E B Bi lt 51 unit CREATE RULE shoelace_upd AS ON UPDATE TO shoelace DO INSTEAD UPDATE shoelace_data SET sl_name NEW sl_name sl_avail NEW sl_avail sl_color NEW sl_color sl len NEW sl len sl unit NEW sl unit WHERE sl name OLD sl name CREATE RULE shoelace del AS ON DELETE TO shoelace DO INSTEAD DELETE FROM shoelace data WHERE sl name OLD sl name Now there is a pack of shoelaces arriving in Al s shop and it has a big part list Al is not that good in calculating and so we don t want him to manually update the shoelace view Instead we setup two little tables one where he can insert the items from the part list and one with a special trick The create commands for these are CREATE TABLE shoelace arrive arr name char 10 arr quant integer 232 Chapter 13 The Rule System CREATE TABLE shoelace ok k name char 10 O O k_quant integer CREATE RULE shoelace_ok_ins AS ON INSERT TO shoelace_ok DO INSTEAD UPDATE shoelace SET sl_avail sl_avail NEW ok_quant WHERE sl_name NEW ok_name Now Al can sit down and do whatever until
95. since you can t normally write INSERT VALUES FROM The FROM clause here is just to indicate that there are range table entries in the parse tree for NEW and OLD These are needed so that they can be referenced by variables in the INSERT command s query tree 229 Chapter 13 The Rule System The rule is a qualified non INSTEAD rule so the rule system has to return two parse trees the modified rule action and the original parse tree In the first step the range table of the original query is incorporated into the rule s action parse tree This results in INSERT INTO shoelace log VALUES NEW sl name NEW sl avail current user current timestamp FROM shoelace data NEW shoelace data OLD shoelace data shoelace data In step 2 the rule qualification is added to it so the result set is restricted to rows where sl avail changes INSERT INTO shoelace log VALUES NEW sl name NEW sl avail current user current timestamp FROM shoelace data NEW shoelace data OLD shoelace data shoelace data WHERE int4ne NEW sl avail OLD sl avail This is even stranger looking since INSERT VALUES doesn t have a WHERE clause either but the planner and executor will have no difficulty with it They need to support this same functionality anyway for INSERT SELECT In step 3 the original parse tree s qualification is added restricting the result set further to only the rows touched
96. so you will need to include at least these two files For portability reasons it s best to include postgres h first before any other system or user header files Including postgres h will also include e1og h and palloc h for you Symbol names defined within object files must not conflict with each other or with symbols defined in the PostgreSQL server executable You will have to rename your functions or variables if you get error messages to this effect Compiling and linking your object code so that it can be dynamically loaded into PostgreSQL always requires special flags See Section 9 5 8 for a detailed explanation of how to do it for your particular operating system 9 5 8 Compiling and Linking Dynamically Loaded Functions Before you are able to use your PostgreSQL extension functions written in C they must be compiled and linked in a special way to produce a file that can be dynamically loaded by the server To be precise a shared library needs to be created For more information you should read the documentation of your operating system in particular the manual pages for the C compiler cc and the link editor 1a In addition the PostgreSQL source code contains several working examples in the contrib directory If you rely on these examples you will make your modules dependent on the availability of the PostgreSQL source code however Creating shared libraries is generally analogous to linking executables first the source fi
97. system error say which If nothing at all happens say so Even if the result of your test case is a program crash or otherwise obvious it might not happen on our platform The easiest thing is to copy the output from the terminal if possible Note In case of fatal errors the error message reported by the client might not contain all the information available Please also look at the log output of the database server If you do not keep your server s log output this would be a good time to start doing so vii Preface The output you expected is very important to state If you just write This command gives me that output or This is not what I expected we might run it ourselves scan the output and think it looks OK and is exactly what we expected We should not have to spend the time to decode the exact semantics behind your commands Especially refrain from merely saying that This is not what SQL says Oracle does Digging out the correct behavior from SQL is not a fun undertaking nor do we all know how all the other relational databases out there behave If your problem is a program crash you can obviously omit this item Any command line options and other start up options including concerned environment variables or configuration files that you changed from the default Again be exact If you are using a prepackaged distribution that starts the database server at boot time you should try to find out how that is done
98. that are part of an inheritance hierarchy may have different fields 190 Chapter 9 Extending SQL Functions than other members of the same inheritance hierarchy Therefore PostgreSQL provides a procedural inter face for accessing fields of composite types from C As PostgreSQL processes a set of rows each row will be passed into your function as an opaque structure of type TUPLE Suppose we want to write a function to answer the query SELECT name c overpaid emp 1500 AS overpaid FROM emp WHERE name Bill OR name Sam In the query above we can define c overpaid as include postgres h include executor executor h for GetAttributeByName bool c overpaid TupleTableSlot t the current row of EMP int32 limit bool isnull int32 salary salary DatumGetInt32 GetAttributeByName t salary amp isnull if isnull return false return salary limit In version 1 coding the above would look like this PG FUNCTION INFO V1 c overpaid Datum Cc overpaid PG FUNCTION ARGS TupleTableSlot t TupleTableSlot PG GETARG POINTER 0 int32 limit PG GETARG INT32 1 bool isnull int32 salary salary DatumGetInt32 GetAttributeByName t salary amp isnull if isnull PG RETURN BOOL false Alternatively we might prefer to do PG RETURN NULL for null salary PG RETURN BOOL salary limit
99. the index s size in pages and tuples is available from the IndexOptInfo struct 3 Estimate the number of index pages that will be retrieved during the scan This might be just indexS electivity times the index s size in pages 4 Compute the index access cost A generic estimator might do this Our generic assumption is that the index pages will be read sequentially so they have cost 1 0 each not random page cost Also we charge for evaluation of the indexquals at each index tuple All the costs are assumed to be paid incrementally during the scan Ey indexStartupCost 0 indexTotalCost numIndexPages cpu index tuple cost cost qual eval indexQuals numIndexTuples 5 Estimate the index correlation For a simple ordered index on a single field this can be retrieved from p8 statistic If the correlation is not known the conservative estimate is zero no correlation Examples of cost estimator functions can be found in src backend utils adt selfuncs c By convention the pg proc entry for an amcostestimate function should show eight arguments all declared as internal since none of them have types that are known to SQL and the return type is void 251 Chapter 16 Triggers PostgreSQL has various server side function interfaces Server side functions can be written in SQL C or any defined procedural language Trigger functions can be written in C and most procedural languages but not in
100. they look like inside If the values of your data type might exceed a few hundred bytes in size in internal form you should be careful to mark them TOAST able To do this the internal representation must follow the standard layout for variable length data the first four bytes must be an int 32 containing the total length in bytes of the datum including itself Then all your functions that accept values of the type must be careful 207 Chapter 10 Extending SQL Types to call pg detoast datum on the supplied values after checking that the value is not NULL if your function is not strict Finally select the appropriate storage option when giving the CREATE TYPE command 208 Chapter 11 Extending SQL Operators 11 1 Introduction PostgreSQL supports left unary right unary and binary operators Operators can be overloaded that is the same operator name can be used for different operators that have different numbers and types of operands If there is an ambiguous situation and the system cannot determine the correct operator to use it will return an error You may have to type cast the left and or right operands to help it understand which operator you meant to use Every operator is syntactic sugar for a call to an underlying function that does the real work so you must first create the underlying function before you can create the operator However an operator is not merely syntactic sugar because
101. to find out where the header files are on the local system pg config includedir usr local include Failure to specify the correct option to the compiler will result in an error message such as testlibpq c 8 22 libpq fe h No such file or directory When linking the final program specify the option 1pq so that the libpq library gets pulled in as well as the option Ldirectory to point it to the directory where the libpq library resides Again the compiler will search some directories by default For maximum portability put the L option before the 1pq option For example cc o testprog testprogl o testprog2 o L usr local pgsql lib lpq You can find out the library directory using pg config as well pg config libdir usr local pgsql lib Error messages that point to problems in this area could look like the following testlibpq o In function main testlibpq o text 0x60 undefined reference to PQsetdbLogin testlibpq o text 0x71 undefined reference to PQstatus testlibpq o text 0xa4 undefined reference to PQerrorMessage This means you forgot 1pq usr bin ld cannot find lpq This means you forgot the L or did not specify the right path If your codes references the header file 1ibpq int h and you refuse to fix your code to not use it starting in PostgreSQL 7 2 this file will be found in includedir postgresqgl internal libpq int h so you need to add the appro
102. to the planner Now we face Al with the problem that the Blues Brothers appear in his shop and want to buy some new shoes and as the Blues Brothers are they want to wear the same shoes And they want to wear them immediately so they need shoelaces too A needs to know for which shoes currently in the store he has the matching shoelaces color and size and where the total number of exactly matching pairs is greater or equal to two We teach him what to do and he asks his database al bundy SELECT FROM shoe ready WHERE total avail gt 2 shoename sh avail sl name sl avail total avail 223 Chapter 13 The Rule System shl 2 s11 5 2 sh3 4 s17 2 rows Alis a shoe guru and so he knows that only shoes of type sh1 would fit shoelace sl7 is brown and shoes that need brown shoelaces aren t shoes the Blues Brothers would ever wear The output of the parser this time is the parse tree SELECT shoe ready shoename shoe ready sh avail shoe ready sl name shoe ready sl avail shoe ready total avail FROM shoe ready shoe ready WHERE int4ge shoe ready total avail 2 The first rule applied will be the one for the shoe ready view and it results in the parse tree SELECT shoe ready shoename shoe ready sh avail shoe ready sl name shoe ready sl avail shoe ready total avail FROM SELECT rsh shoename rsh sh avail rsl sl name rsl sl avail min rsh sh a
103. to the secretaries view will fail Someone might think that this rule by rule checking is a security hole but in fact it isn t If this would not work the secretary could setup a table with the same columns as phone number and copy the data to there once per day Then it s his own data and he can grant access to everyone he wants A GRANT means T trust you If someone you trust does the thing above it s time to think it over and then REVOKE This mechanism does also work for update rules In the examples of the previous section the owner of the tables in Al s database could GRANT SELECT INSERT UPDATE and DELETE on the shoelace view to al But only SELECT on shoelace log The rule action to write log entries will still be executed successfully And AI could see the log entries But he cannot create fake entries nor could he manipulate or remove existing ones Warning GRANT ALL currently includes RULE permission This means the granted user could drop the rule do the changes and reinstall it think this should get changed quickly 13 6 Rules and Command Status The PostgreSQL server returns a command status string such as INSERT 149592 1 for each query it receives This is simple enough when there are no rules involved but what happens when the query is rewritten by rules As of PostgreSQL 7 3 rules affect the command status as follows 238 Chapter 13 The Rule System 1 If there is no unconditional INSTEAD rule for th
104. used to build a function that converts result list strings to their correct type using a hardcoded table definition The number returned is the field rank in the result values list 154 ntuples Name ntuples return the number of tuples in query object Synopsis ntuples Parameters none Return Type integer The number of tuples in query object Exceptions SyntaxError Too many arguments Description ntuples method returns the number of tuples found in a query 155 6 6 Large Object pglarge open This object handles all the request concerning a PostgreSQL large object It embeds and hides all the recurrent variables object OID and connection exactly in the same way pgobjects do thus only keeping significant parameters in function calls It keeps a reference to the pgob ject used for its creation sending requests though with its parameters Any modification but dereferencing the pgob ject will thus affect the pglarge object Dereferencing the initial pgobject is not a problem since Python will not deallocate it before the large object dereference it All functions return a generic error message on call error whatever the exact error was The error attribute of the object allows to get the exact error message pglarge objects define a read only set of attributes that allow to get some information about it These attributes are oid the OID associated with the object pgcnx the pgobject a
105. used to return multiple rows or columns from the function The function opens the cursor and returns the cursor name to the caller The caller can then FETCH rows from the cursor The cursor can be closed by the caller or it will be closed automatically when the transaction closes The cursor name returned by the function can be specified by the caller or automatically generated The following example shows how a cursor name can be supplied by the caller CREATE TABLE test col text INSERT INTO test VALUES 123 CREATE FUNCTION reffunc refcursor RETURNS refcursor AS EGIN UJ 328 D amp Chapter 19 PL pgSQL SQL Procedural Language OPEN 1 FOR SELECT col FROM test ETURN 1 2 ANGUAGE plpgsql UJ EGIN n ny ELECT reffunc funccursor ETCH ALL IN funccursor COMMIT The following example uses automatic cursor name generation CREATE FUNCTION reffunc2 RETURNS refcursor AS DECLARE ref refcursor BEGIN OPEN ref FOR SELECT col FROM test RETURN ref END LANGUAGE plpgsql UJ EGIN SELECT reffunc2 reffunc2 lt 1 unnamed cursor 1 gt row FETCH ALL IN lt unnamed cursor 1 gt COMMIT 19 8 Errors and Messages Use the RAISE statement to report messages and raise errors RAISI Possible leve
106. users to allow users to define set returning functions that do not have this limitation Currently the point at which data begins being written to disk is controlled by the SORT MEM configuration variable Administrators who have sufficient memory to store larger result sets in memory should consider increasing this parameter 19 6 2 Conditionals IF statements let you execute commands based on certain conditions PL pgSQL has four forms of IF IF HEN IF HEN S IF THEN ELSE IF and e IE 2 HEN ELSIF THEN ELSE 19 6 2 1 rF THEN IF boolean expression THEN statements END IF IF THEN statements are the simplest form of IF The statements between THEN and END IF will be executed if the condition is true Otherwise they are skipped IF v user id 0 THEN UPDATE users SET email v email WHERE user id v user id END IF 19 6 2 2 IF THEN ELSE IF boolean expression THEN statements ELSE statements END IF IF THEN ELSE statements add to IF THEN by letting you specify an alternative set of statements that should be executed if the condition evaluates to FALSE IF parentid IS NULL or parentid THEN 321 return fullname ELSE END IF IF v count gt 0 THEN INSERT INTO users count count return t ELSE return f END IF 19 6 2 3 IF TH
107. usually called PL PerlU In this case the full Perl language is available If the createlang program is used to install the language the language name plperlu will select the untrusted PL Perl variant The writer of a PL PerlU function must take care that the function cannot be used to do anything unwanted since it will be able to do anything that could be done by a user logged in as the database administrator Note that the database system allows only database superusers to create functions in untrusted languages If the above function was created by a superuser using the language plper1u execution would succeed 2 http www cpan org modules by module DBD APILOS 3 http www cpan org SITES html 354 Chapter 21 PL Perl Perl Procedural Language 21 5 Missing Features The following features are currently missing from PL Perl but they would make welcome contributions PL Perl functions cannot call each other directly because they are anonymous subroutines inside Perl There s presently no way for them to share global variables either PL Perl cannot be used to write trigger functions DBD PgSPI or similar capability should be integrated into the standard PostgreSQL distribution 355 Chapter 22 PL Python Python Procedural Language The PL Python procedural language allows PostgreSQL functions to be written in the Python language To install PL Python in a particular database use createlang plpython
108. value fixed length pass by reference fixed length pass by reference variable length By value types can only be 1 2 or 4 bytes in length also 8 bytes if sizeof Datum is 8 on your machine You should be careful to define your types such that they will be the same size in bytes on all architectures For example the Long type is dangerous because it is 4 bytes on some machines and 8 bytes on others whereas int type is 4 bytes on most Unix machines A reasonable implementation of the int4 type on Unix machines might be 4 byte integer passed by value typedef int int4 PostgreSQL automatically figures things out so that the integer types really have the size they advertise On the other hand fixed length types of any size may be passed by reference For example here is a sample implementation of a PostgreSQL type 16 byte structure passed by reference 184 Chapter 9 Extending SQL Functions typedef struct double x y Point Only pointers to such types can be used when passing them in and out of PostgreSQL functions To return a value of such a type allocate the right amount of memory with pa11oc fill in the allocated memory and return a pointer to it Alternatively you can return an input value of the same type by returning its pointer Never modify the contents of a pass by reference input value however Finally all variable length types must also be passed by reference All variable
109. var2 list 203 ECPG TOO MANY MATCHES Too many matches line d This means the query has returned several rows but the variables specified are not arrays The S command was not unique 204 ECPG INT FORMAT Not correctly formatted int type s line d ECT This means the host variable is of type int and the field in the PostgreSQL database is of another type and contains a value that cannot be interpreted as an int The library uses st rtol for this conversion 205 ECPG UINT FORMAT Not correctly formatted unsigned type s line d This means the host variable is of type unsigned int and the field in the PostgreSQL database is of another type and contains a value that cannot be interpreted as an unsigned int The library uses strtoul for this conversion 206 ECPG FLOAT FORMAT Not correctly formatted floating point type s line d This means the host variable is of type float and the field in the PostgreSQL database is of another type and contains a value that cannot be interpreted as a float The library uses st rtod for this conversion 207 ECPG CONVERT BOOL Unable to convert s to bool on line d This means the host variable is of type boo1 and the field in the PostgreSQL database is neither t nor f 208 ECPG EMPTY Empty query line d The query was empty This cannot normally happen in an embedded SQL program so it ma
110. way to work around this is to split the procedure in three different functions one to return the host another for the path and another for the query CREATE OR REPLACE PROCEDURE cs parse url v url IN VARCHAR v host OUT VARCHAR This will be passed back v path OUT VARCHAR This one too v query OUT VARCHAR And this one is a posl INTEGER a pos2 INTEGER begin v host NULL v path NULL V query NULL a posl instr v url PostgreSQL doesn t have an instr function IF a posl 0 THEN RETURN END IF a pos2 instr v url a posl 2 IF a pos2 0 THEN v host substr v url a posl 2 337 Chapter 19 PL pgSQL SQL Procedural Language v path RETURN END IF v host substr v url a posl 2 a pos2 a posl 2 a posl instr v url a pos2 1 THEN substr v url IF a_posl 0 v_path RETURN END IF a_pos2 substr v_url a posl a pos2 substr v url a pos2 a posl 1 v path fe v query END show errors Here is how this procedure could be translated for PostgreSQL CREATE OR REPLACE FUNCTION cs parse url host VARCHAR DECLARE v url ALIAS FOR 1 VARCHAR VARCHA INTEGE INTEGE INTEGE host Dm uU ou 4 5 O n ct ll NULL Eey Urie ZAA
111. with that name is looked up among the variables that were previously declared within a EXEC SOL DECLARE section Depending on whether the variable is being use for input or output a pointer to the variable is output to allow access by the function For every variable that is part of the SQL query the function gets other arguments The type as a special symbol A pointer to the value or a pointer to the pointer The size of the variable if itis a char or varchar The number of elements in the array for array fetches The offset to the next element in the array for array fetches The type of the indicator variable as a special symbol A pointer to the value of the indicator variable or a pointer to the pointer of the indicator variable 0 Number of elements in the indicator array for array fetches The offset to the next element in the indicator array for array fetches Note that not all SQL commands are treated in this way For instance an open cursor statement like EX EC SQL OPI EN cursor is not copied to the output Instead the cursor s DECLARE command is used because it opens the cursor as well Here is a complete example describing the output of the preprocessor of a file oo pgc details may change with each particular version of the preprocessor EX EC SOL B EGIN DECLARE S ECTION int index in
112. www ibm com 4 http meteora ucsd edu s2k s2k home html Preface Benchmark compared to POSTGRES Version 4 2 Apart from bug fixes the following were the major enhancements The query language PostQUEL was replaced with SQL implemented in the server Subqueries were not supported until PostgreSQL see below but they could be imitated in Postgres95 with user defined SQL functions Aggregates were re implemented Support for the GROUP BY query clause was also added The 1ibpq interface remained available for C programs In addition to the monitor program a new program psql was provided for interactive SQL queries using GNU Readline A new front end library 1ibpgtcl supported Tcl based clients A sample shell pgtclsh provided new Tcl commands to interface Tcl programs with the Postgres95 backend The large object interface was overhauled The Inversion large objects were the only mechanism for storing large objects The Inversion file system was removed The instance level rule system was removed Rules were still available as rewrite rules A short tutorial introducing regular SQL features as well as those of Postgres95 was distributed with the source code GNU make instead of BSD make was used for the build Also Postgres95 could be compiled with an unpatched GCC data alignment of doubles was fixed 2 3 PostgreSQL By 1996 it became clear that the name Postgres95 would not stand the test of tim
113. you are to return to Executor if UPDATE and you don t want to replace this tuple with another one or skip the operation tg trigger is pointer to structure Trigger defined in utils rel h typedef struct Trigger Oid tgoid char tgname Oid tgfoid int16 tgtype bool tgenabled bool tgisconstraint Oid tgconstrrelid bool tgdeferrable bool tginitdeferred int16 tgnargs int16 tgattr FUNC MAX ARGS char tgargs Trigger where tgname is the trigger s name tgnargs is number of arguments in tgargs tgargs is an array of pointers to the arguments specified in the CREATE TRIGGER statement Other members are for internal use only 255 Chapter 16 Triggers 16 3 Visibility of Data Changes PostgreSQL data changes visibility rule during a query execution data changes made by the query itself via SQL function SPI function triggers are invisible to the query scan For example in query INSERT INTO a SELECT FROM a tuples inserted are invisible for SELECT scan In effect this duplicates the database table within itself subject to unique index rules of course without recursing But keep in mind this notice about visibility in the SPI documentation Changes made by query Q are visible by queries that are started after query Q no matter whether they are started inside Q during the execution of Q or after Q is done This is true for triggers as well so though a tuple being inserted tg t rigtu
114. 13 The Rule System Noqualification and not INSTEAD The parse tree from the rule action where the original parse tree s qualification has been added Noqualification but INSTEAD The parse tree from the rule action where the original parse tree s qualification has been added Qualification given and not INSTEAD The parse tree from the rule action where the rule qualification and the original parse tree s qualifi cation have been added Qualification given and INSTEAD The parse tree from the rule action where the rule qualification and the original parse tree s qualifi cation have been added The original parse tree where the negated rule qualification has been added Finally if the rule is not INSTEAD the unchanged original parse tree is added to the list Since only qualified INSTEAD rules already add the original parse tree we end up with either one or two output parse trees for a rule with one action For ON INSERT rules the original query if not suppressed by INSTEAD is done before any actions added by rules This allows the actions to see the inserted row s But for ON UPDATE and ON DELETE rules the original query is done after the actions added by rules This ensures that the actions can see the to be updated or to be deleted rows otherwise the actions might do nothing because they find no rows matching their qualifications The parse trees generated from rule actions are thrown into the rewr
115. 327 Chapter 19 PL pgSQL SQL Procedural Language 19 7 3 Using Cursors Once a cursor has been opened it can be manipulated with the statements described here These manipulations need not occur in the same function that opened the cursor to begin with You can return a re cursor value out of a function and let the caller operate on the cursor Internally a refcur sor value is simply the string name of a Portal containing the active query for the cursor This name can be passed around assigned to other refcursor variables and so on without disturbing the Portal All Portals are implicitly closed at transaction end Therefore a refcursor value is useful to reference an open cursor only until the end of the transaction 19 7 3 1 FETCH FETCH cursor INTO target FETCH retrieves the next row from the cursor into a target which may be a row variable a record variable or a comma separated list of simple variables just like SELECT INTO As with SELECT INTO the special variable FOUND may be checked to see whether a row was obtained or not FETCH cursl INTO rowvar FETCH curs2 INTO foo bar baz 19 7 3 2 CLOSE CLOSE cursor CLOSE closes the Portal underlying an open cursor This can be used to release resources earlier than end of transaction or to free up the cursor variable to be opened again CLOSE cursi 19 7 3 3 Returning Cursors PL pgSQL functions can return cursors to the caller This is
116. 61 62 query 52 reading 59 writing 60 PGUSER pg_config pg_conndefaults 46 pg_connect 43 45 47 48 50 pg ctl pg dumpall pg execute 52 pg function is visible pg get constraintdef pg get indexdef pg get ruledef pg get userbyid pg get viewdef pg hba conf pg ident conf pg lo close 58 pg lo creat 56 pg lo export 65 364 pg lo import 64 pg lo Iseek 61 pg lo open 57 pg lo read 59 pg lo tell 62 pg lo unlink 63 pg lo write 60 pg opclass is visible pg operator is visible pg table is visible pg type is visible phantom read PIC PL Perl 352 PL pgSQL 307 PL Python 356 PL SQL 333 PL Tcl 345 point polygon port postgres user postmaster ps to monitor activity psql Python 356 qualified names query quotes and identifiers escaping R tree See indexes range table readline real record referential integrity regclass regoper Index regoperator regproc regprocedure regression test regtype regular expressions See Also pattern matching reindex relation relational database row rules 217 and views 219 schema current schemas current schema SCO OpenServer search path changing at runtime current search_path SELECT select list semaphores sequences and seri
117. 7 2 is the first release of the JDBC Driver that supports the bytea data type The introduction of this functionality in 7 2 has introduced a change in behavior as compared to previous releases In 7 2 the methods getBytes setBytes getBinaryStream and setBinaryStream operate on the bytea data type In 7 1 these methods operated on the OID data type associated with Large Objects It is possible to revert the driver back to the old 7 1 behavior by setting the compat ible property on the Connection to a value of 7 1 To use the bytea data type you should simply use the getBytes setBytes getBinaryS tream OrsetBinaryStream methods 82 Chapter 5 JDBC Interface To use the Large Object functionality you can use either the LargeObject API provided by the Post greSQL JDBC Driver or by using the get BLOB and set BLOB methods Important For PostgreSQL you must access Large Objects within an SQL transaction You would open a transaction by using the setAutoCommit method with an input parameter of false Note In a future release of the JDBC Driver the getBLoB and setBLOB methods may no longer interact with Large Objects and will instead work on bytea data types So it is recommended that you use the LargeOb ject API if you intend to use Large Objects Example 5 4 Binary Data Examples For example suppose you have a table containing the file name of an image and you also want to store the image in a bytea co
118. COMMIT 67 Deleting rows EXEC SQL DELETE FROM foo WHERE EXEC SOL COMMIT Singleton Select EXEC SOL SELECT foo INTO FooBar FROM tablel WH Select using Cursors number EXEC SQL DECLARE foo bar CURSOR FOR SELECT number ascii FROM foo ORDER BY ascii EXEC SQL FETCH foo bar INTO FooBar EXEC SQL CLOSE foo bar EXEC SQL COMMIT Updates EXEC SQL UPDATE foo SET ascii foobar WHERE number 9999 EXEC SQL COMMIT Chapter 4 ECPG Embedded SQL in C 9999 ERE ascii doodad DooDad The tokens of the form something are host variables that is they refer to variables in the C program They are explained in the next section In the default mode statements are committed only when EC SQL COMMIT is issued The embed EX ded SQL interface also supports autocommit of transactions as known from other interfaces via the t command line option to ecpg see below or via the SET AUTOCOMMIT TO ON statement In EXEC SOL autocommit mode each query is automatically committed unless it is inside an explicit transaction block EXEC SQL S ET AUTOCOMMIT TO OFF This mode can be explicitly turned off using 4 5 Passing Data To pass data from t
119. CT lo export image raster tmp motd FROM image WHERE name beautiful image 2 5 Accessing Large Objects from Libpq Example 2 1 is a sample program which shows how the large object interface in libpq can be used Parts of the program are commented out but are left in the source for the reader s benefit This program can be found in src test examples testlo c in the source distribution Frontend applications which use the large object interface in libpq should include the header file 1ibpq 1libpq fs h and link with the libpq library Example 2 1 Large Objects with Libpq Example Program testlo c a test using large objects with libpq Copyright c 1994 Regents of the University of California include lt stdio h gt include libpq fe h include libpq libpq fs h 35 Chapter 2 Large Objects define BUFSIZE 1024 importFile A import file in filename into database as large object lobjOid Oid importFile PGconn conn char filename Oid 10bjId int lobj fd char buf BUFSIZE int nbytes tmp int fd open the file to be read in fd open filename O RDONLY 0666 if fd 0 error fprintf stderr can t open unix file s n filename create the large object lobjId lo creat conn INV READ INV WRITE if lobjId 0 fprintf stderr can t create large object n lobj
120. E E E t E nu 118 Betdefportza snee n EI deli i RO RE E m E E EEE 119 set defpott sor e Ern Regatta REP 120 ROI G 121 set detopt xeu reni eth Cem pone RS des 122 pet deftty ine ree met oe pee t sd E OASE SS 123 set deftty iiS Reni i EET US Pers 124 Bet defbases eR RI ORT REO NA SER CERE IR 125 setdetbases sei e eite ee tierce ere ere pet cedes ete 126 6 3 Connection Object pgob jection aa E E EEE E E 127 QUeELy A A A E A E E E T E E A 127 TESS bers E di a A ESE ded aU ee a ee E 129 CLOSE 130 AICNO mE XE 131 POMOULY ss EE 132 1Inserttable e A EE ER UU ee Dem 133 putlime s seen ime Dm eme eoer iibi eec ee PEERS 134 Bethe sic cm ha ti ai eae ka tien eic etes 135 endcopy oue eee ROT Dn eepotiepieme tea PEE 136 locreate eb s nbus 137 getlo cessas Oase geo Hem iae daos io ER 138 loim pott e oerte enc ep RE Un DRE REI iie trece qudis 139 6 4 Database Wrapper Class DB oet ettet tpe 140 PREY us ueoeg depu REOR E ROSQUNIR RORIS 140 get databases iiti UO a ORE ur EE 142 OW HH 143 Bet AattDam es nci ri e ERR TURNER Gass AREE RR E E E 144 11A E E oio Qe PR IRR ER CE ree re e rie nueve eee steer E 145 IDSeTt os ennt Do uei gan es 146 updatea EE 147 CLEAR Foes ossia Ree ees ee ee ee addi 148 delete xecnestseieuuewle ee EU P DS 149 6 5 Query Result Object pgqueryob ject eeseeseeeseesee eene enne nnne ettet nennen en
121. ELECT execq SELECT FROM a 10 INFO EXECQ 0 301 Chapter 17 Server Programming Interface INFO EXECQ 1 INFO EXECQ 2 lt lt lt 0 2 only one tuple inserted as specified 3 lt lt lt 10 is max value only 3 is real of tuples vac gt DELETE FROM a DELETE 3 vac gt INSERT INTO a VALU INSERT 167712 1 vac gt SELECT FROM a x GI S execq SELECT FROM a 0 1 q lt lt lt no tuples ina 0 1 1 row vac gt INSERT INTO a VALUES execq SELECT FROM a 0 1 INFO EXECQ 0 INSERT 167713 1 vac gt SELECT FROM a x 1 2 lt lt lt there was single tuple ina 1 2 rows This demonstrates data changes visibility rule vac gt INSERT INTO a SELECT execq SELECT FROM a 0 x FROM a INFO EXECQ 1 INFO EXECO INFO EXECO INFO EXECO INFO EXECO INSERT 0 2 vac SELECT FROM a NO ON FN lt lt lt 3 tuples 2 1 just inserted 2 x in second tuple 4 rows RAKRAKRAAKRA tuples visible to execq in different invocations 1 2 2 lt lt lt 2 tuples 1 x in first tuple 6 302 Ill Procedural Languages This part documents the procedural languages available in the PostgreSQL distribution as well as general issues concerning procedural language
122. EN ELSE IF Chapter 19 PL pgSQL SQL Procedural Language return hp true filename parentid VALU IF statements can be nested as in the following example IF demo row sex m THEN pretty sex man ELSE IF demo row sex f THEN pretty sex woman END IF END IF I TTE fullname S v count When you use this form you are actually nesting an IF statement inside the ELSE part of an outer IF statement Thus you need one END IF statement for each nested IF and one for the parent IF ELSE This is workable but grows tedious when there are many alternatives to be checked 19 6 2 4 IF THEN ELSIF ELSE IF boolean expression THEN statements ELSIF boolean expression TH statements ELSIF boolean expression THEN statements 1 ELSE statements END IF IF THEN ELSIF ELSE provides a more convenient method of checking many alternatives in one state ment Formally it is equivalent to nested IF needed Here is an example IH EN ELS p LE TH EN commands but only one END IF is 322 Chapter 19 PL pgSQL SQL Procedural Language IF number 0 THEN result zero ELSIF number gt 0 THEN result positive ELSIF number lt 0 THEN result negative iSE hmm the only other possibility is that number IS NULL result NU
123. END LANGUAGE plpgsql The real tables we need in the first two rule system descriptions are these CREATE TABLE shoe data shoename char 10 primary key sh avail integer available of pairs slcolor char 10 preferred shoelace color slminlen float miminum shoelace length slmaxlen float maximum shoelace length slunit char 8 length unit CREATE TABL I shoelace data sl name char 10 primary key sl avail integer available of pairs sl color char 10 shoelace color sl len float shoelace length sl unit char 8 length unit CREATE TABLE unit un name char 8 the primary key un fact float factor to transform to cm 220 i Chapter 13 The Rule System I think most of us wear shoes and can realize that this is really useful data Well there are shoes out in the world that don t require shoelaces but this doesn t make Al s life easier and so we ignore it The views are created as CREATE VIEW shoe AS SELECT sh shoename sh sh_avail sh slcolor sh slminlen sh slminlen un un_fact AS slminlen_cm sh slmaxlen sh slmaxlen un un_fact AS slmaxlen_cm sh slunit FROM shoe_data sh unit un WHERE sh slunit un un_name CREATE VIEW shoelace AS SELECT s sl_name s sl_avail SS Leolo s sl_len s sl unit s s
124. ETURN v user id LANGUAGE plpgsql ER VARCHAR TIMESTAMP INT EG EG ER INT acs user new user id object type creation date creation user creation 341 Chapter 19 PL pgSQL SQL Procedural Language 19 11 5 Other Things to Watch For 19 11 5 1 EXECUTE The PostgreSQL version of EXECUTE works nicely but you have to remember to use quote literal TEXT and quote string TEXT as described in Section 19 5 4 Constructs of the type EXECUTE SELECT from 1 will not work unless you use these functions 19 11 5 2 Optimizing PL pgSQL Functions PostgreSQL gives you two function creation modifiers to optimize execution iscachable function always returns the same result when given the same arguments and isstrict function returns NULL if any argument is NULL Consult the CREATE FUNCTION reference for details To make use of these optimization attributes you have to use the WITH modifier in your CR EAT E FUNC TION statement Something like CREATE FUNCTION foo RETURNS INTEGER AS LANGUAGE plpgsql WITH isstrict iscachable 19 11 6 Appendix 19 11 6 1 Code for my instr functions instr functions that mimic Oracle s counterpart Syntax instr stringl string2 n m where denotes optional params Searches stringl beginning at the nth character for the mth
125. F nm T LANGUAGE plpgsql Written by Robert Gaszewski graszew poland com Licensed under the GPL v2 or later CREATE FUNCTION instr VARCHAR VARCHAR INTEGER INTEGER RETURNS INTEGER AS DECLARE string ALIAS FOR 1 string to search ALIAS FOR 2 beg index ALIAS FOR 3 occur index ALIAS FOR 4 343 Chapter 19 PL pgSQL SQL Procedural Language pos integer NOT NULL DEFAULT 0 occur number INTEGER NOT NULL DEFAULT 0 temp str VARCHAR beg INTEGER i INTEGER length INTE GER Ss length INTEGER BEGIN IF beg index gt 0 THEN beg beg index temp str substring string FROM beg index FOR i IN 1 occur index LOOP pos position string to search IN temp str IF i 1 THEN beg beg pos 1 ELSE beg beg pos END IF temp_str substring string FROM beg 1 END LOOP IF pos 0 THEN RETURN 0 ELS RETURN beg END IF ELSE ss_length char_length string_to_search length char length string beg length beg index Ss length 2 WHILE beg 0 LOOP temp str substring string FROM beg FOR ss length pos position string to search IN temp str IF pos 0 THEN occur number occur number 1 IF occur number occur index
126. G o foo so foo o Tru64 UNIX PIC is the default so the compilation command is the usual one 1d with special options is used to do the linking C foo c ld shared xpect_unresolved o foo so foo o The same procedure is used with GCC instead of the system compiler no special options are re quired UnixWare The compiler flag to create PIC is K PIC with the SCO compiler and pic with GCC To link shared libraries the compiler option is G with the SCO compiler and shared with GCC Go EK PIG S amp T Loose cc G o foo so foo o or gce fpic G foocc gcc shared o foo so foo o 201 Chapter 9 Extending SQL Functions Tip If you want to package your extension modules for wide distribution you should consider using GNU Libtool for building shared libraries It encapsulates the platform differences into a general and powerful interface Serious packaging also requires considerations about library versioning symbol resolution methods and other issues The resulting shared library file can then be loaded into PostgreSQL When specifying the file name to the CREATE FUNCTION command one must give it the name of the shared library file not the intermediate object file Note that the system s standard shared library extension usually so or s1 can be omitted from the CREATE FUNCTION command and normally should be omitted for best portability Refer back to Section 9 5 1 about where the server
127. GUAGE plperl If an SQL null value is passed to a function the argument value will appear as undefined in Perl The above function definition will not behave very nicely with null inputs in fact it will act as though they are zeroes We could add STRICT to the function definition to make PostgreSQL do something more reasonable if a null value is passed the function will not be called at all but will just return a null result automatically Alternatively we could check for undefined inputs in the function body For example suppose that we wanted perl max with one null and one non null argument to return the non null argument rather than a null value CREATE FUNCTION perl max integer integer RETURNS integer AS my a b 8 if defined a l http www perl com 352 Chapter 21 PL Perl Perl Procedural Language if defined b return undef return b if defined b return a if a gt b return a return Sb LANGUAGE plperl As shown above to return an SQL null value from a PL Perl function return an undefined value This can be done whether the function is strict or not Composite type arguments are passed to the function as references to hashes The keys of the hash are the attribute names of the composite type Here is an example CREATE TABLE employee name text basesalary integer bonus integer CREATE FUNCTI
128. L Functions on Base Types essent 176 9 2 3 SQL Functions on Composite Types sssseeeeeeeeeeeenen enne 177 9 24 SOL Table Functions eS estet t atem te ate 179 9 2 5 SQL Functions Returning Sets essesesseeeeeeeeee eene 179 9 3 Procedural Language Functions eseseseeeeeeeeeeee eene eren nennen 181 9 4 Internal Functions nter ei eooo En AET EEE EE SEn EEE Er TES 181 9 5 C Language FUCHS seir etit eeo ere e EEE r EO reet RE E EErEE ei 181 9 5 1 Dynamic Lo ding icosoie nee otio sa ESERE OESS DESE s STE TERS RES 182 9 5 2 Base Types in C Language FunctionSs esessesesesseseesssrererrererrsreersrrerrrrsreeesreee 183 9 5 3 Version 0 Calling Conventions for C Language Functions 185 9 5 4 Version 1 Calling Conventions for C Language Functions 188 9 5 5 Composite Types in C Language Functions esee 190 95 6 Table Function API o oce terrre te ede evite bn 192 9 5 6 1 Returning Rows Composite Types eee 192 9 5 6 2 Ret rning Sets cueste nhe Hedge deo etie ittis 193 9 5 7 Writing Code osse iin ge tuner 198 9 5 8 Compiling and Linking Dynamically Loaded Functions 199 9 6 Function Overloading s poti nee dtp d EES E Te Eos 202 97 Table Functions oun ee eO perg PEE OUR REUS 203 9 8 Procedural Langua
129. L pgSQL EXECUTE statement at the price of constructing a new query plan on every execution Note The PL pgSQL EXECUTE statement is not related to the EXECUTE statement supported by the PostgreSQL backend The backend EXECUTE statement cannot be used within PL pgSQL functions and is not needed Except for input output conversion and calculation functions for user defined types anything that can be defined in C language functions can also be done with PL pgSQL It is possible to create complex conditional computation functions and later use them to define operators or use them in functional indexes 19 1 1 Advantages of Using PL pgSQL Better performance see Section 19 1 1 1 SQL support see Section 19 1 1 2 Portability see Section 19 1 1 3 19 1 1 1 Better Performance SQL is the language PostgreSQL and most other relational databases use as query language It s portable and easy to learn But every SQL statement must be executed individually by the database server That means that your client application must send each query to the database server wait for it to process it receive the results do some computation then send other queries to the server All this incurs inter process communication and may also incur network overhead if your client is on a different machine than the database server With PL pgSQL you can group a block of computation and a series of queries inside the database server thus having the power
130. LE lt lt label gt gt WHILE expression LOOP statements END LOOP The WHILE statement repeats a sequence of statements so long as the condition expression evaluates to true The condition is checked just before each entry to the loop body For example WHILE amount owed gt 0 AND gift certificate balance gt 0 LOOP some computations here END LOOP WHILE NOT boolean expression LOOP some computations here END LOOP 19 6 3 4 FOR END This form FOR integer for loop label gt gt name IN REVERSE expression expression LOOP statements LOOP of FOR creates a loop that iterates over a range of integer values The variable name is auto matically defined as type integer and exists only inside the loop The two expressions giving the lower and upper bound of the range are evaluated once when entering the loop The iteration step is normally 1 but is 1 when REVERSE is specified 324 Chapter 19 PL pgSQL SQL Procedural Language Some examples of integer FOR loops FOR i IN 1 10 LOOP some expressions here RAISE NOTICE i is i END LOOP FOR i IN REVERSE 10 1 LOOP some expressions here END LOOP 19 6 4 Looping Through Query Results Using a different type of FOR loop you can iterate through the results of a query and manipulate that data accordingly The syntax is lt lt label gt
131. LException on conversion failure PGcircle This constructor is used by the driver void setValue String s throws SQLException Parameters S definition of the circle in PostgreSQL s syntax Throws SQLException on conversion failure Overrides setValue in class PGobject boolean equals Object obj Parameters obj Object to compare with Returns true if the two circles are identical Overrides equals in class PGobject Object clone This must be overridden to allow the object to be cloned Overrides clone in class PGobject String getValue Returns the PGcircle in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGline java lang Object 93 Chapter 5 JDBC Interface t org postgresql util PGobject t org postgresql geometric PGline public class PGline extends PGobject implements Serializable Cloneable This implements a line consisting of two points Currently line is not yet implemented in the backend but this class ensures that when it s done were ready for it Variables public PGpoint point These are the two points Constructors public PGline double x1 double yl double x2 double y2 Parameters xl coordinate for first point yl coordinate for first point x2 coordinate for second point y2 coordinate for second point public PGline PGpoint pl PGpoint p2 Parameters pl firs
132. LL END IF The final ELSE section is optional 19 6 3 Simple Loops With the LOOP EXIT WHILE and FOR statements you can arrange for your PL pgSQL function to repeat a series of commands 19 6 3 1 LOOP lt lt label gt gt LOOP statements END LOOP LOOP defines an unconditional loop that is repeated indefinitely until terminated by an EXIT or RETURN statement The optional label can be used by EXIT statements in nested loops to specify which level of nesting should be terminated 19 6 3 2 EXIT EXIT label WHEN expression If no label is given the innermost loop is terminated and the statement following END LOOP is ex ecuted next If label is given it must be the label of the current or some outer level of nested loop or block Then the named loop or block is terminated and control continues with the statement after the loop s block s corresponding END If WHEN is present loop exit occurs only if the specified condition is true otherwise control passes to the statement after EXIT Examples LOOP some computations IF count 0 THEN EXIT exit loop 323 END Chapter 19 PL pgSQL SQL Procedural Language END IF 00P LOOP some computations EXIT WHEN count 0 END LOOP BEGI some computations IF stocks 100000 THEN EXIT illegal Can t use EXIT outside of a LOOP END IF END 19 6 3 3 WHI
133. ON empcomp employee RETURNS integer AS my Semp Q return Semp gt basesalary Semp gt bonus LANGUAGE plperl SELECT name empcomp employee FROM employee There is currently no support for returning a composite type result value Tip Because the function body is passed as an SQL string literal to CREATE FUNCTION you have to escape single quotes and backslashes within your Perl source typically by doubling them as shown in the above example Another possible approach is to avoid writing single quotes by using Perl s extended quoting operators q aat1 aw 1 21 2 Data Values in PL Perl The argument values supplied to a PL Perl function s script are simply the input arguments converted to text form just as if they had been displayed by a SELECT statement Conversely the return command will accept any string that is acceptable input format for the function s declared return type So the PL Perl programmer can manipulate data values as if they were just text 353 Chapter 21 PL Perl Perl Procedural Language 21 3 Database Access from PL Perl Access to the database itself from your Perl function can be done via an experimental module DBD PgSPI also available at CPAN mirror sites This module makes available a DBI compliant database handle named pg_dbh that can be used to perform queries with normal DBI syntax PL Perl itself presently provid
134. OTIFY messages which include the PID of the notifying backend Note that the PID belongs to a process executing on the database server host not the local host PQgetssl Returns the SSL structure used in the connection or NULL if SSL is not in use SSL PQgetssl const PGconn conn This structure can be used to verify encryption levels check server certificate and more Refer to the SSL documentation for information about this structure You must define USE_SSL in order to get the prototype for this function Doing this will also automati cally include ss1 h from OpenSSL Chapter 1 libpq C Library 1 3 Command Execution Functions Once a connection to a database server has been successfully established the functions described here are used to perform SQL queries and commands 1 3 1 Main Routines PQexec Submit a command to the server and wait for the result PGresult PQexec PGconn conn const char query Returns a PGresult pointer or possibly a NULL pointer A non NULL pointer will generally be re turned except in out of memory conditions or serious errors such as inability to send the command to the backend If a NULL is returned it should be treated like a PGRES FATAL ERROR result Use PQerrorMessage to get more information about the error The PGresult structure encapsulates the result returned by the backend 1ibpq application programmers should be careful to maintain the PGresult abstract
135. One advantage of spi execp is that you don t have to quote argument values like this since the arguments are never parsed as part of an SQL query string elog level msg Emit a log or error message Possible levels are DEBUG LOG INFO NOTICE WARNING ERROR and FATAL Most simply emit the given message just like the elog backend C function ERROR raises an error condition further execution of the function is abandoned and the current transaction is aborted FATAL aborts the transaction and causes the current backend to shut down there is probably no good reason to use this error level in PL Tcl functions but it s provided for completeness 20 2 5 Trigger Procedures in PL Tcl Trigger procedures can be written in PL Tcl As is customary in PostgreSQL a procedure that s to be called as a trigger must be declared as a function with no arguments and a return type of trigger The information from the trigger manager is passed to the procedure body in the following variables STG_name The name of the trigger from the CREATE TRIGGER statement STG_relid The object ID of the table that caused the trigger procedure to be invoked 349 Chapter 20 PL Tcl Tcl Procedural Language STG_relatts A Tcl list of the table field names prefixed with an empty list element So looking up an element name in the list with Tcl s 1search command returns the element s number starting with 1 for the first column the same way the
136. PI ERROR COPY if COPY TO FROM stdin SPI ERROR CURSOR if DECLARE CLOSE CURSOR FETCH SPI ERROR TRANSACTION if BEGIN ABORT END SPI ERROR OPUNKNOWN if type of query is unknown this shouldn t occur If execution of your query was successful then one of the following non negative values will be returned SPI OK UTILITY if some utility e g CREATE TABLE was executed SPI OK SELECT if SELECT but not SELECT INTO was executed SPI OK SELINTO if SELECT INTO was executed SPI OK INSERT if INSERT or INSERT SELECT was executed SPI OK DELETE if DELETE was executed SPI OK UPDATE if UPDATE was executed 263 SPI exec Description SPI exec creates an execution plan parser planner optimizer and executes the query for tcount tuples Usage This should only be called from a connected procedure If t count is zero then it executes the query for all tuples returned by the query scan Using t count gt 0 you may restrict the number of tuples for which the query will be executed much like a LIMIT clause For example SPI exec INSERT INTO tab SELECT FROM tab 5 will allow at most 5 tuples to be inserted into table If execution of your query was successful then a non negative value will be returned Note You may pass multiple queries in one string or query string may be re written by RULEs SPI exec returns the result for the last query executed The actual number of tuples for which t
137. PI prepare Note However there is a disadvantage since the planner does not know the values that will be supplied for the parameters it may make worse query planning choices than it would make for a simple query with all constants visible If the query uses parameters their number and data types must be specified in the call to SPI prepare The plan returned by SPI prepare may be used only in current invocation of the procedure since SPI finish frees memory allocated for a plan But see SPI saveplan to save a plan for longer If successful a non null pointer will be returned Otherwise you ll get a NULL plan In both cases SPI result will be set like the value returned by SPI exec except that it is set to SPI ERROR ARGUMENT if query is NULL or nargs lt 0 or nargs gt 0 amp amp argtypes is NULL 267 SPI execp Name SPI execp Executes a plan from SPI prepare Synopsis SPI execp plan values nulls tcount Inputs void plan Execution plan Datum values Actual parameter values char nulls Array describing which parameters are NULLs n indicates NULL values entry ignored space indicates not NULL values entry is valid int tcount Number of tuples for which plan is to be executed Outputs int Returns the same value as SPI exec as well as SPI ERROR ARGUMENT if p1anis NULL or tcount 0 SPI ERROR PARAM if values is NULL and plan was prepared with some parameters SPI tuptable initialized
138. PL SQL and PostgreSQL s PL pgSQL languages in the hopes of helping developers port applications from Oracle to PostgreSQL Most of the code here is from the ArsDigita Clickstream module that I ported to PostgreSQL when I took an internship with OpenForce Inc in the Summer of 2000 PL pgSQL is similar to PL SQL in many aspects It is a block structured imperative language all variables have to be declared PL SQL has many more features than its PostgreSQL counterpart but PL pgSQL allows for a great deal of functionality and it is being improved constantly l http www arsdigita com 2 http www arsdigita com asj clickstream 3 http www openforce net 333 19 11 1 Main Differences Some things you should keep in mind when porting from Oracle to PostgreSQL No default parameters in PostgreSQL Chapter 19 PL pgSQL SQL Procedural Language You can overload functions in PostgreSQL This is often used to work around the lack of default pa rameters Assignments loops and conditionals are similar No need for cursors in PostgreSQL just put the query in the FOR statement see example below In PostgreSQL you need to escape single quotes See Section 19 11 1 1 19 11 1 1 Quote Me on That Escaping Single Quotes In PostgreSQL you need to escape single quotes inside your function definition This can lead to quite amusing code at times especially if you are creating a function that generates other function
139. PostgreSQL 7 3 2 Programmer s Guide The PostgreSQL Global Development Group PostgreSQL 7 3 2 Programmer s Guide by The PostgreSQL Global Development Group Copyright 1996 2002 by The PostgreSQL Global Development Group Legal Notice PostgreSQL is Copyright 1996 2002 by the PostgreSQL Global Development Group and is distributed under the terms of the license of the University of California below Postgres95 is Copyright 1994 5 by the Regents of the University of California Permission to use copy modify and distribute this software and its documentation for any purpose without fee and without a written agreement is hereby granted provided that the above copyright notice and this paragraph and the following two paragraphs appear in all copies IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR DIRECT INDIRECT SPECIAL INCI DENTAL OR CONSEQUENTIAL DAMAGES INCLUDING LOST PROFITS ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES INCLUDING BUT NOT LIMITED TO THE IM PLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE THE SOFTWARE PROVIDED HERE UNDER IS ON AN AS IS BASIS AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE SUPPORT UPDATES ENHANCEMENTS OR MODIFICATIONS Table of Cont
140. Procedural Language PL pgSQL is a loadable procedural language for the PostgreSQL database system This package was originally written by Jan Wieck This documentation was in part written by Roberto Mello lt rmello fslc usu edu gt 19 1 Overview The design goals of PL pgSQL were to create a loadable procedural language that can be used to create functions and trigger procedures adds control structures to the SQL language can perform complex computations inherits all user defined types functions and operators can be defined to be trusted by the server is easy to use The PL pgSQL call handler parses the function s source text and produces an internal binary instruction tree the first time the function is called within any one backend process The instruction tree fully trans lates the PL pgSQL statement structure but individual SQL expressions and SQL queries used in the function are not translated immediately As each expression and SQL query is first used in the function the PL pgSQL interpreter creates a pre pared execution plan using the SPI manager s SPI prepare and SPI saveplan functions Subsequent visits to that expression or query re use the prepared plan Thus a function with conditional code that con tains many statements for which execution plans might be required will only prepare and save those plans that are really used during the lifetime of the database connection This can substantially r
141. QL command for information on correct values for these environment variables 21 Chapter 1 libpq C Library 1 11 Files The file pgpass in the home directory is a file that can contain passwords to be used if the connection requires a password This file should have the format hostname port database username password Any of these may be a literal name or which matches anything The first matching entry will be used so put more specific entries first When an entry contains or it must be escaped with The permissions on pgpass must disallow any access to world or group achieve this by the command chmod 0600 pgpass If the permissions are less strict than this the file will be ignored 1 12 Threading Behavior libpg is thread safe as of PostgreSQL 7 0 so long as no two threads attempt to manipulate the same PGconn object at the same time In particular you cannot issue concurrent queries from different threads through the same connection object If you need to run concurrent queries start up multiple connections PGresult objects are read only after creation and so can be passed around freely between threads The deprecated functions POoidStatus and fe setauthsvc are not thread safe and should not be used in multithread programs PQoidStatus can be replaced by PQoidValue There is no good reason to call fe setauthsvo at all Libpq clients using the crypt encryption method rely on the crypt operating system func
142. QL standard port number 5432 database The database name To connect you need to get a Connection instance from JDBC To do this you would use the Driver Manager getConnection method Connection db DriverManager getConnection url username password 79 Chapter 5 JDBC Interface 5 2 4 Closing the Connection To close the database connection simply call the close method to the Connection db close 5 3 Issuing a Query and Processing the Result Any time you want to issue SQL statements to the database you require a Statement or Prepared Statement instance Once you have a Statement or PreparedStatement you can use issue a query This will return a ResultSet instance which contains the entire result Example 5 1 illustrates this pro cess Example 5 1 Processing a Simple Query in JDBC This example will issue a simple query and print out the first column of each row using a Statement Statement st db createStatement ResultSet rs st executeQuery SELECT FROM mytable where columnfoo 500 while rs next System out print Column 1 returned System out println rs getString 1 rs close st close This example will issue the same query as before using a PreparedStatement and a bind value in the query int foovalue 500 PreparedStatement st db prepareStatement SELECT FROM mytable where colum nfoo st setInt 1 fooval
143. Throws SQLException if a database access error occurs or no result public void addFunction String name int fnid This adds a function to our look up table User code should use the addFunctions method which is based upon a query rather than hard coding the OID The OID for a function is not guaranteed to remain static even on different servers of the same version public void addFunctions ResultSet rs throws SQLException This takes a ResultSet containing two columns Column contains the function name Column 2 the OID It reads the entire ResultSet loading the values into the function table Important Remember to c1ose the ResultSet after calling this Implementation note about function name look ups PostgreSQL stores the function id s and their corresponding names in the pa proc table To speed things up locally instead of querying each function from that table when required a Hashtable is used Also only the function s required are entered into this table keeping connection times as fast as possible The org postgresql LargeObject class performs a query upon its start up and passes the re turned ResultSet to the aadFunctions method here Once this has been done the Large Object API refers to the functions by name Do not think that manually converting them to the OIDs will work OK they will for now but they can change during development there was some discussion about this for V7 0 so this is implemented to
144. a buffer suitable to hold the resultant escaped string length The result string length includes the terminating zero byte of the result PQescapeBytea returns an escaped version of the from parameter binary string to a caller provided buffer The return string has all special characters replaced so that they can be properly processed by the PostgreSQL string literal parser and the bytea input function A terminating zero byte is also added The single quotes that must surround PostgreSQL string literals are not part of the result string PQunescapeBytea Converts an escaped string representation of binary data into binary data the reverse of PQescapeBytea unsigned char PQunescapeBytea unsigned char from size t to length The from parameter points to an escaped string such as might be returned by POget value of a BYTEA column PQunescapeBytea converts this string representation into its binary representation filling the supplied buffer It returns a pointer to the buffer which is NULL on error and the size of the buffer in to length The pointer may subsequently be used as an argument to the function ree 3 1 3 4 Retrieving SELECT Result Information POntuples Returns the number of tuples rows in the query result int POntuples const PGresult res POnfields Returns the number of fields columns in each row of the query result int PQnfields const PGresult res PQfname Returns the field column name associa
145. a subselect qualification that in total uses 4 nesting joined views where one of them itself has a subselect qualification containing a view and where calculated view columns are used gets rewritten into one single parse tree that deletes the requested data from a real table I think there are only a few situations out in the real world where such a construct is necessary But it makes me feel comfortable that it works The truth is Doing this I found one more bug while writing this document But after fixing that I was a little amazed that it works at all 13 5 Rules and Permissions Due to rewriting of queries by the PostgreSQL rule system other tables views than those used in the original query get accessed Using update rules this can include write access to tables Rewrite rules don t have a separate owner The owner of a relation table or view is automatically the owner of the rewrite rules that are defined for it The PostgreSQL rule system changes the behavior of the default access control system Relations that are used due to rules get checked against the permissions 237 Chapter 13 The Rule System of the rule owner not the user invoking the rule This means that a user does only need the required permissions for the tables views he names in his queries For example A user has a list of phone numbers where some of them are private the others are of interest for the secretary of the office He can construct the following
146. a working connection is lost They differ from POreset above in that they act in a nonblocking manner These functions suffer from the same restrictions as POconnect Start and POconnectPoll Call POresetStart If it returns 0 the reset has failed If it returns 1 poll the reset using POreset Poll in exactly the same way as you would create the connection using POconnectPoll libpq application programmers should be careful to maintain the PGconn abstraction Use the accessor functions below to get at the contents of PGconn Avoid directly referencing the fields of the PGconn structure because they are subject to change in the future Beginning in PostgreSQL release 6 4 the definition of struct PGconn is not even provided in 1ibpq fe h If you have old code that accesses PGconn fields directly you can keep using it by including 1ibpq int h too but you are encouraged to fix the code soon PQdb Returns the database name of the connection char PQdb const PGconn conn PQdb and the next several functions return the values established at connection These values are fixed for the life of the PGconn object PQuser Returns the user name of the connection char PQuser const PGconn conn POpass Returns the password of the connection char PQpass const PGconn conn PQhost Returns the server host name of the connection char PQhost const PGconn conn POport Returns the port of the connection char PQport const PGc
147. able 3 1 pgtc1 Commands Command Description lg connect opens a connection to the backend server log disconnect closes a connection pg conndefaults get connection options and their defaults pg exec send a query to the backend pg result manipulate the results of a query pg select loop over the result of a SELECT statement lg execute send a query and optionally loop over the results lg listen establish a callback for NOTIFY messages pg on connection loss establish a callback for unexpected connection loss pg lo creat create a large object Ig lo open open a large object pg lo close close a large object pg lo read read a large object pg lo write write a large object log lo lseek seek to a position in a large object log lo tell return the current seek position of a large object lg lo unlink delete a large object log lo import import a Unix file into a large object lg lo export export a large object into a Unix file The pg 1o routines are interfaces to the large object features of PostgreSQL The functions are de signed to mimic the analogous file system functions in the standard Unix file system interface The pg lo routines should be used within a BEGIN COMMIT transaction block because the file descriptor returned by pg 1o open is only valid for the current transaction pg 1o import and pg lo
148. actually contain any initialization script you need it normally defines a Tcl unknown procedure that is invoked whenever Tcl does not recognize an invoked procedure name PL Tcl s standard version of this procedure tries to find a module in pltcl_modules that will define the required procedure If one is found it is loaded into the interpreter and then execution is allowed to proceed with the originally attempted procedure call A secondary table pltcl_modfuncs provides an index of which functions are defined by which modules so that the lookup is reasonably quick The PostgreSQL distribution includes support scripts to maintain these tables pltcl loadmod pltcl listmod pltcl delmod as well as source for the standard unknown module share unknown pltcl This module must be loaded into each database initially to support the autoloading mechanism The tables pltcl modules and pltcl modfuncs must be readable by all but it is wise to make them owned and writable only by the database administrator 20 2 7 Tcl Procedure Names In PostgreSQL one and the same function name can be used for different functions as long as the number of arguments or their types differ Tcl however requires all procedure names to be distinct PL Tcl deals with this by making the internal Tcl procedure names contain the object ID of the procedure s pg proc row as part of their name Thus PostgreSQL functions with the same name and different argument types will b
149. age DISTINCT double precision DROP TABLE duplicate dynamic loading dynamic library path elog PL Perl embedded SQL in C 66 environment variables 20 error message escaping binary strings 9 escaping strings 9 except exists Index extending SQL 171 types 171 false FETCH embedded SQL files 21 flex float4 See real float8 See double precision floating point foreign key formatting FreeBSD fsync function 175 203 internal 181 SQL 175 functions genetic query optimization GEQO See genetic query optimization get bit get byte group GROUP BY hash See indexes has database privilege has function privilege has language privilege has schema privilege has table privilege HAVING hierarchical database HP UX 362 ident identifiers in index scan indexes B tree hash multicolumn on functions partial R tree unique inet data type inheritance initlocation input function INSERT installation on Windows int2 See smallint int4 See integer int8 See bigint integer internal intersection interval IRIX IS NULL isolation levels read committed read serializable join outer self joins cross left natural outer Index Kerberos key
150. ages Synopsis pg listen dbHandle notifyName callbackCommand Inputs dbHandle Specifies a valid database handle notifyName Specifies the notify condition name to start or stop listening to callbackCommand If present provides the command string to execute when a matching notification arrives Outputs None Description pg listen creates changes or cancels a request to listen for asynchronous NOTIFY messages from the PostgreSQL backend With a ca11backCommand parameter the request is established or the command string of an already existing request is replaced With no ca11backCommand parameter a prior request is canceled After a pg listen request is established the specified command string is executed whenever a NOTIFY message bearing the given name arrives from the backend This occurs when any PostgreSQL client application issues a NOTIFY command referencing that name Note that the name can be but does not have to be that of an existing relation in the database The command string is executed from the Tcl idle loop That is the normal idle state of an application written with Tk In non Tk Tcl shells you can execute update or vwait to cause the idle loop to be entered You should not invoke the SQL statements LISTEN or UNLISTEN directly when using pg listen Pgtcl takes care of issuing those statements for you But if you want to send a NOTIFY message yourself invoke the SQL NOTIFY statement using pg exec
151. ailable 78 Chapter 5 JDBC Interface This is the most common method to use but restricts your code to use just PostgreSQL If your code may access another database system in the future and you do not use any PostgreSQL specific extensions then the second method is advisable The second method passes the driver as a parameter to the JVM as it starts using the D argument Example java Djdbc drivers org postgresql Driver example ImageViewer In this example the JVM will attempt to load the driver as part of its initialization Once done the Im ageViewer is started Now this method is the better one to use because it allows your code to be used with other database packages without recompiling the code The only thing that would also change is the connection URL which is covered next One last thing When your code then tries to open a Connection and you get a No driver available SOLException being thrown this is probably caused by the driver not being in the class path or the value in the parameter not being correct 5 2 3 Connecting to the Database With JDBC a database is represented by a URL Uniform Resource Locator With PostgreSQL this takes one of the following forms jdbc postgresql database jdbc postgresql host database jdbc postgresql host port database where host The host name of the server Defaults to localhost port The port number the server is listening on Defaults to the PostgreS
152. aining the query to be executed This string is fed literally to the SOL engine Note in particular that no substitution of PL pgSQL variables is done on the query string The values of variables must be inserted in the query string as it is constructed When working with dynamic queries you will have to face escaping of single quotes in PL pgSQL Please refer to the table in Section 19 11 for a detailed explanation that will save you some effort Unlike all other queries in PL pgSQL a query run by an EXECUTE statement is not prepared and saved just once during the life of the server Instead the query is prepared each time the statement is run The query string can be dynamically created within the procedure to perform actions on variable tables and fields The results from SELECT queries are discarded by EXECUTE and SELECT INTO is not currently supported within EXECUTE So the only way to extract a result from a dynamically created SELECT is to use the FOR IN EXECUTE form described later An example EXECUTE UPDATE tbl SET quote ident fieldname Wile mtus m quote literal newvalue pU WHERE Q3 This example shows use of the functions quote ident TEXT and quote literal TEXT Variables containing field and table identifiers should be passed to function quote ident Variables containing literal elements of the dynamic query string should be passed to quote literal Both tak
153. al type sequential scan serial serial4 serial8 SETOF See Also function setting current set setval set_bit set_byte shared libraries shared memory SHMMAX SIGHUP similar to 365 sliced bread See TOAST smallint Solaris some sorting query results SPI allocating space 294 295 296 297 298 299 connecting 260 266 268 276 copying tuple descriptors 290 copying tuples 288 291 cursors 270 272 273 274 275 decoding tuples 278 280 281 283 285 286 287 disconnecting 262 executing 263 modifying tuples 292 SPI_connect 260 SPI copytuple 288 SPI copytupledesc 290 SPI copytupleintoslot 291 SPI cursor close 275 SPI cursor fetch 273 SPI cursor find 272 SPI cursor move 274 SPI cursor open 270 SPI exec 263 SPI execp 268 SPI finish 262 SPI fname 280 SPI fnumber 278 SPI freeplan 299 SPI freetuple 297 SPI freetuptable 298 SPI getbinval 283 SPI getrelname 287 SPI gettype 285 SPI gettypeid 286 SPI getvalue 281 spi lastoid SPI modifytuple 292 SPI palloc 294 SPI pfree 296 SPI prepare 266 SPI repalloc 295 SPI saveplan 276 Index ssh SSL standard deviation statistics strings See character strings subqueries subquery substring sum superuser syntax SQL table Tcl 41 345 TCP IP text See charact
154. ame way than the Unix close function 158 read Name read read from the large object Synopsis read size Parameters size Maximal size of the buffer to be read integer Return Type string The read buffer Exceptions TypeError Bad parameter type or too many arguments IOError Object is not opened or read error pg error Invalid connection or invalid object Description read method allows to read data from the large object starting at current position 159 write Name write write to the large object Synopsis write string Parameters string Buffer to be written string Return Type none Exceptions TypeError Bad parameter type or too many arguments IOError Object is not opened or write error pg error Invalid connection or invalid object Description write method allows to write data to the large object starting at current position 160 seek Name seek change current position in the large object Synopsis seek offset whence Parameters offset Position offset integer whence Positional parameter integer Return Type integer New current position in the object Exceptions TypeError Bad parameter type or too many arguments IOError Object is not opened or seek error pg error Invalid connection or invalid object Description seek method allows to move the cursor posit
155. apter 19 PL pgSQL SQL Procedural Language s ETURNS VARCHAR AS DECLARE v name ALIAS FOR 1 v version ALIAS FOR 2 BEGI IF v version IS NULL THEN return v name D IF ETURN v name v version w m LANGUAGE plpgsql Example 19 6 A Function that Creates Another Function The following procedure grabs rows from a SELECT statement and builds a large function with the results in IF statements for the sake of efficiency Notice particularly the differences in cursors FOR loops and the need to escape single quotes in PostgreSQL CREATE OR REPLACE PROCEDURE cs update referrer type proc IS CURSOR referrer keys IS SELECT FROM cs referrer keys ORDER BY try order a output VARCHAR 4000 BEGIN a output CREATE OR REPLACE FUNCTION cs find referrer type v host IN VAR CHAR v domain IN VARCHAR v url IN VARCHAR RETURN VARCHAR IS BEGIN FOR referrer_key IN referrer_keys LOOP a output a output IF v referrer key kind LIKE referrer key key string THEN RETURN referrer key referrer type v s END IF END LOOP a output a output RETURN NULL END EXECUTE IMMEDIATE a output END show errors Here is how this function would end up in PostgreSQL CREATE FUNCTION cs update referrer type
156. apter 5 JDBC Interface public class PGpoint extends PGobject implements Serializable Cloneable This implements a version of java awt Point except it uses double to represent the coordinates It maps to the point data type in PostgreSQL Variables public double x The X coordinate of the point public double y The Y coordinate of the point Constructors public PGpoint double x double y Parameters X coordinate y coordinate public PGpoint String value throws SQLException 99 Chapter 5 JDBC Interface This is called mainly from the other geometric types when a point is embedded within their definition Parameters value Definition of this point in PostgreSQL s syntax public PGpoint Required by the driver Methods public void setValue String s throws SQLException Parameters S Definition of this point in PostgreSQL s syntax Throws SQLException on conversion failure Overrides setValue in class PGobject public boolean equals Object obj Parameters obj Object to compare with Returns true if the two points are identical Overrides equals in class PGobject public Object clone This must be overridden to allow the object to be cloned Overrides clone in class PGobject public String getValue Returns the PGpoint in the syntax expected by PostgreSQL Overrides getValue in class PGobject public void translate int x int y
157. as in SPI exec if successful 268 SPI execp SPI processed initialized as in SPI exec if successful Description SPI execp executes a plan prepared by SPI prepare tcount has the same interpretation as in SPI exec Usage If nulls is NULL then SPI execp assumes that all parameters if any are NOT NULL Note If one of the objects a relation function etc referenced by the prepared plan is dropped during your session by your backend or another process then the results of sP1 execp for this plan will be unpredictable 269 SPI cursor open Name SPI cursor open Sets up a cursor using a plan created with SPI prepare Synopsis SPI cursor open name pian values nulls Inputs char name Name for portal or NULL to let the system select a name void plan Execution plan Datum values Actual parameter values char nulls Array describing which parameters are NULLs n indicates NULL values entry ignored space indicates not NULL values entry is valid Outputs Portal Pointer to Portal containing cursor or NULL on error Description SPI cursor open sets up a cursor internally a Portal that will execute a plan prepared by SPI prepare Using a cursor instead of executing the plan directly has two benefits First the result rows can be retrieved a few at a time avoiding memory overrun for queries that return many rows Second a Portal can outlive 270 SPI cursor open the current
158. ation syntax which in general is name CURSOR arguments FOR select query FOR may be replaced by Is for Oracle compatibility argument s if any are a comma separated list of name datatype pairs that define names to be replaced by parameter values in the given query The actual values to substitute for these names will be specified later when the cursor is opened Some examples DECLARE cursl refcursor curs2 CURSOR FOR SELECT from tenkl curs3 CURSOR key int IS SELECT from tenkl where uniquel key All three of these variables have the data type refcursor but the first may be used with any query while the second has a fully specified query already bound to it and the last has a parameterized query bound to it key will be replaced by an integer parameter value when the cursor is opened The variable curs1 is said to be unbound since it is not bound to any particular query 326 Chapter 19 PL pgSQL SQL Procedural Language 19 7 2 Opening Cursors Before a cursor can be used to retrieve rows it must be opened This is the equivalent action to the SQL command DECLARE CURSOR PL pgSQL has four forms of the OPEN statement two of which use unbound cursor variables and the other two use bound cursor variables 19 7 2 1 OPEN FOR SELECT OPEN unbound cursor FOR SELECT The cursor variable is opened and given the specified query to execu
159. avior is not portable You might get a run time linker error or one of the functions will get called usually the internal one The alternative form of the AS clause for the SQL CREATE FUNCTION command decouples the SQL function name from the function name in the C source code E g CREATE FUNCTION test int RETURNS int AS filename test larg ANGUAGE C CREATE FUNCTION test int int RETURNS int AS filename test 2arg ANGUAGE C The names of the C functions here reflect one of many possible conventions l http www gnu org software libtool 202 Chapter 9 Extending SQL Functions Prior to PostgreSQL 7 0 this alternative syntax did not exist There is a trick to get around the problem by defining a set of C functions with different names and then define a set of identically named SQL function wrappers that take the appropriate argument types and call the matching C function 9 7 Table Functions Table functions are functions that produce a set of rows made up of either base scalar data types or composite multi column data types They are used like a table view or subselect in the FROM clause of a query Columns returned by table functions may be included in SELECT JOIN or WHERE clauses in the same manner as a table view or subselect column If a table function returns a base data type the single result column is named for the function
160. base name user User name to connect as password Password to be used if the server demands password authentication connect timeout Time space in seconds given to connect routine Zero or not set means infinite options tty Trace debug options to be sent to the server A file or tty for optional debug output from the backend requiressl Set to 1 to require SSL connection to the server Libpq will then refuse to connect if the server does not accept an SSL connection Set to 0 default to negotiate with server This option is only available if PostgreSQL is compiled with SSL support Chapter 1 libpq C Library If any parameter is unspecified then the corresponding environment variable see Section 1 10 is checked If the environment variable is not set either then hardwired defaults are used The return value is a pointer to an abstract st ruct representing the connection to the backend PQsetdbLogin Makes a new connection to the database server PGconn PQsetdbLogin const char pghost const char pgport const char pgoptions const char pgtty const char dbName const char login const char pwd This is the predecessor of POconnectdb with a fixed number of parameters but the same functionality PQsetdb Makes a new connection to the database server PGconn PQsetdb char pghost char pgport char pgoptions char pgtty char dbName This is a macro that calls POset dbLogin with nul
161. ber of improvements because the macros can hide unnecessary detail An example is that in coding add one float8 we no longer need to be aware that float8 is a pass by reference type Another example is that the GETARG macros for variable length types hide the need to deal with fetching toasted compressed or out of line values The old style copytext and con cat text functions shown above are actually wrong in the presence of toasted values because they don t call pg detoast datum on their inputs The handler for old style dynamically loaded func tions currently takes care of this detail but it does so less efficiently than is possible for a version 1 function One big improvement in version 1 functions is better handling of NULL inputs and results The macro PG ARGISNULL n allows a function to test whether each input is NULL of course doing this is only necessary in functions not declared strict As with the PG GETARG xxx macros the input arguments are counted beginning at zero Note that one should refrain from executing PG GETARG xxx until one has verified that the argument isn t NULL To return a NULL result execute PG RETURN NULL this works in both strict and nonstrict functions Other options provided in the new style interface are two variants of the PG GETARG xxx macros The first of these PG GETARG xxx COPY guarantees to return a copy of the specified parameter which is saf
162. bject handles a connection to the PostgreSQL database It embeds and hides all the parameters that define this connection leaving just really significant parameters in function calls Some methods give direct access to the connection socket They are specified by the tag DA Do not use them unless you really know what you are doing If you prefer disabling them set the DNO DIRECT option in the Python Setup file Some other methods give access to large objects if you want to forbid access to these from the module set the DNO LARGE option in the Python Setup file These methods are specified by the tag LO Every pgobject defines a set of read only attributes that describe the connection and its status These attributes are host the host name of the server string port the port of the server integer db the selected database string options the connection options string tty the connection debug terminal string user user name on the database system string status the status of the connection integer 1 OK 0 bad error the last warning error message from the server string Name query execute a SQL command 127 query Synopsis query command Parameters command SQL command string Return Type pgqueryobject Or None Result values Exceptions TypeError Bad argument type or too many arguments ValueError Empty SQL query pg error Error during q
163. bugging tty for the backend s change this to the name of your test database database 29 Chapter 1 libpq C Library conn PQsetdb pghost pgport pgoptions pgtty dbName check to see that the backend connection was successfully made x if PQstatus conn CONNECTION BAD fprintf stderr Connection to database s failed n dbName fprintf stderr Ss PQerrorMessage conn exit nicely conn start a transaction block res PQexec conn BEGIN if res PQresultStatus res PGRES COMMAND OK fprintf stderr BEGIN command failed n POclear res exit nicely conn should PQclear PGresult whenever it is no longer needed to avoid memory leaks ae PQclear res fetch rows from the pg_database the system catalog of databases nid res PQexec conn DECLARE mycursor BINARY CURSOR FOR SELECT FROM test1 if res PQresultStatus res PGRES COMMAND OK fprintf stderr DECLARE CURSOR command failed n PQclear res exit nicely conn POclear res res PQexec conn FETCH ALL in mycursor if res PQresultStatus res PGRES TUPLES OK fprintf stderr FETCH ALL command didn t return tuples properly n PQclear res exit nicely conn i fnum PQfnumber res i POfnumber res d POfnumber res p d fnum p fnum
164. built a tuple to return from your function the tuple must be converted into a Datum Use TupleGetDatum TupleTableSlot slot HeapTuple tuple to get a Datum given a tuple and a slot This Datum can be returned directly if you intend to return just a single row or it can be used as the current return value in a set returning function An example appears below 193 Chapter 9 Extending SQL Functions 9 5 6 2 Returning Sets A set returning function SRF is normally called once for each item it returns The SRF must there fore save enough state to remember what it was doing and return the next item on each call The Table Function API provides the FuncCallContext structure to help control this process fcinfo gt flinfo fn extra is used to hold a pointer to FuncCallContext across calls typedef struct Number of times we ve been called befor call cntr is initialized to 0 for you by SRF FIRSTCALL INIT and incremented for you every time SRF RETURN NEXT is called uint32 call cntr OPTIONAL maximum number of calls max calls is here for convenience ONLY and setting it is OPTIONAL If not set you must provide alternative means to know when the function is done a uint32 max_calls OPTIONAL pointer to result slot slot is for use when returning tuples i e composite data types and is not needed when returning base i e scalar data types Tupl
165. bute isn t touched So the rule qualified or not will only do its scans if there ever could be something to do Rules will only be significantly slower than triggers if their actions result in large and bad qualified joins a situation where the planner fails They are a big hammer Using a big hammer without caution can cause big damage But used with the right touch they can hit any nail on the head 241 Chapter 14 Interfacing Extensions To Indexes 14 1 Introduction The procedures described thus far let you define new types new functions and new operators However we cannot yet define a secondary index such as a B tree R tree or hash access method over a new type nor associate operators of a new type with secondary indexes To do these things we must define an operator class for the new data type We will describe operator classes in the context of a running example a new operator class for the B tree access method that stores and sorts complex numbers in ascending absolute value order Note Prior to PostgreSQL release 7 3 it was necessary to make manual additions to pg amop pg amproc and pg opclass in order to create a user defined operator class That approach is now deprecated in favor of using CREATE OPERATOR CLASS Which is a much simpler and less error prone way of creating the necessary catalog entries 14 2 Access Methods and Operator Classes The pg am table contains one row for every index access method Sup
166. c A response of PORES EMPTY QUERY often exposes a bug in the client software PQresStatus Converts the enumerated type returned by PQresultStatus into a string constant describing the status code char PQresStatus ExecStatusType status Chapter 1 libpq C Library PQresultErrorMessage returns the error message associated with the query or an empty string if there was no error char PQOresultErrorMessage const PGresult res Immediately following a PQexec or POgetResult call PQerrorMessage on the connection will return the same string as POresultErrorMessage on the result However a PGresult will retain its error message until destroyed whereas the connection s error message will change when subsequent operations are done Use POresultErrorMessage when you want to know the status associated with a particular PGresult use POerrorMessage when you want to know the status from the latest oper ation on the connection POclear Frees the storage associated with the PGresult Every query result should be freed via POclear when it is no longer needed void PQclear PQresult res You can keep a PGresult object around for as long as you need it it does not go away when you issue a new query nor even if you close the connection To get rid of it you must call PQclear Failure to do this will result in memory leaks in the frontend application PQmakeEmptyPGresult Constructs an empty PGresult object with th
167. c PGpolygon PGpoint points Creates a polygon using an array of PGpoints Parameters points the points defining the polygon public PGpolygon String s throws SQLException Parameters S definition of the polygon in PostgreSQL s syntax Throws SQLException on conversion failure public PGpolygon Required by the driver Methods public void setValue String s throws SQLException Parameters S Definition of the polygon in PostgreSQL s syntax Throws SQLException on conversion failure 102 Chapter 5 JDBC Interface Overrides setValue in class PGobject public boolean equals Object obj Parameters obj Object to compare with Returns true if the two polygons are identical Overrides equals in class PGobject public Object clone This must be overridden to allow the object to be cloned Overrides clone in class PGobject public String getValue Returns the PGpolygon in the syntax expected by PostgreSQL Overrides getValue in class PGobject 5 7 3 Large Objects Large objects are supported in the standard JDBC specification However that interface is limited and the API provided by PostgreSQL allows for random access to the objects contents as if it was a local file The org postgresql largeobject package provides to Java the libpq C interface s large object API It consists of two classes LargeOb jectManager which deals with creating opening and deleting large
168. clauses only make sense for binary operators that return boolean The idea behind a join selectivity estimator is to guess what fraction of the rows in a pair of tables will satisfy a WHERE clause condition of the form tablel columnl OP table2 column2 for the current operator As with the RESTRICT clause this helps the optimizer very substantially by letting it figure out which of several possible join sequences is likely to take the least work As before this chapter will make no attempt to explain how to write a join selectivity estimator function but will just suggest that you use one of the standard estimators if one is applicable eqjoinsel for neqjoinsel for lt gt scalarltjoinsel for lt or lt scalargtjoinsel for gt or gt areajoinsel for 2D area based comparisons positionjoinsel for 2D position based comparisons cont joinsel for 2D containment based comparisons 11 3 5 HASHES The HASHES clause if present tells the system that it is permissible to use the hash join method for a join based on this operator HASHES only makes sense for binary operators that return boolean and in practice the operator had better be equality for some data type The assumption underlying hash join is that the join operator can only return true for pairs of left and right values that hash to the same hash code If two values get put in different hash buckets the join will never compare them at all implicitly assu
169. computer it can use the statement 239 Chapter 13 The Rule System DELETE FROM software WHERE hostname 1 in a prepared and saved plan and pass the nost name in the parameter The rule would be written as CREATE RULE computer del AS ON DELETE TO computer DO DELETE FROM software WHERE hostname OLD hostname Now we look at different types of deletes In the case of a DELETE FROM computer WHERE hostname mypc local net the table computer is scanned by index fast and the query issued by the trigger would also be an index scan fast too The extra query from the rule would be a DELETE FROM software WHERE computer hostname mypc local net AND software hostname computer hostname Since there are appropriate indexes setup the planner will create a plan of Nestloop Index Scan using comp hostidx on computer Index Scan using soft hostidx on software So there would be not that much difference in speed between the trigger and the rule implementation With the next delete we want to get rid of all the 2000 computers where the hostname starts with old There are two possible queries to do that One is DELETE FROM computer WHERE hostname gt old AND hostname lt ole Where the plan for the rule query will be a Hash Join Seq Scan on software Hash
170. costs of retrieving or processing the main table tuples that are identified by the index The start up cost is the part of the total scan cost that must be expended before we can begin to fetch the first tuple For most indexes this can be taken as zero but an index type with a high start up cost might want to set it nonzero The indexSelectivity should be set to the estimated fraction of the main table tuples that will be retrieved during the index scan In the case of a lossy index this will typically be higher than the fraction of tuples that actually pass the given qual conditions The indexCorrelation should be set to the correlation ranging between 1 0 and 1 0 between the index order and the table order This is used to adjust the estimate for the cost of fetching tuples from the main table 250 Chapter 15 Index Cost Estimation Functions Cost Estimation A typical cost estimator will proceed as follows 1 Estimate and return the fraction of main table tuples that will be visited based on the given qual conditions In the absence of any index type specific knowledge use the standard optimizer function clauselist selectivity indexSelectivity clauselist selectivity root indexQuals lfirsti rel gt relids 2 Estimate the number of index tuples that will be visited during the scan For many index types this is the same as indexSelectivity times the number of tuples in the index but it might be more Note that
171. cture Save these two global variables into local procedure variables if you need to access the result of one sP1 exec Or SPI execp across later calls SPI finish frees all SPITupleTables allocated during the current procedure You can free a particular result table earlier if you are done with it by calling SPI freetuptable 265 SPI prepare Name SPI prepare Prepares a plan for a query without executing it yet Synopsis SPI prepare query nargs argtypes Inputs query Query string nargs Number of input parameters 1 nargs as in SQL functions argtypes Pointer to array of type OIDs for input parameter types Outputs void Pointer to an execution plan parser planner optimizer Description SPI prepare creates and returns an execution plan parser planner optimizer but doesn t execute the query Should only be called from a connected procedure Usage When the same or similar query is to be executed repeatedly it may be advantageous to perform query planning only once SPI prepare converts a query string into an execution plan that can be passed repeatedly to SPI execp A prepared query can be generalized by writing parameters 1 2 etc in place of what would be con stants in a normal query The values of the parameters are then specified when SPI execp is called This allows the prepared query to be used over a wider range of situations than would be possible without parameters 266 S
172. d indexed by the field names This is ignored if querySt ring is nota SELECT statement For SELECT statements if this option is not used result tuples values are stored in individual variables named according to the field names in the result oid oz dVar Specifies the name of a variable into which the OID from an INSERT statement will be stored dbHandle Specifies a valid database handle queryString Specifies a valid SQL query queryProcedure Optional command to execute for each result tuple of a SELECT statement Outputs ntuples The number of tuples affected or returned by the query Description pg execute submits a query to the PostgreSQL backend If the query is not a SELECT statement the query is executed and the number of tuples affected by the query is returned If the query is an INSERT and a single tuple is inserted the OID of the inserted tuple is stored in the oi dVar variable if the optional oid argument is supplied 22 pg execute If the query is a SELECT statement the query is executed For each tuple in the result the tuple field values are stored in the arrayVar variable if supplied using the field names as the array indexes else in variables named by the field names and then the optional queryProcedure is executed if supplied Omitting the queryProcedure probably makes sense only if the query will return a single tuple The number of tuples selected is returned The queryProcedure can use th
173. d a restriction selectivity estimator is to guess what fraction of the rows in a table will satisfy a WHERE clause condition of the form column OP constant for the current operator and a particular constant value This assists the optimizer by giving it some idea of how many rows will be eliminated by WHERE clauses that have this form What happens if the constant is on the left you may be wondering Well that s one of the things that COMMUTATOR is for Writing new restriction selectivity estimation functions is far beyond the scope of this chapter but fortu nately you can usually just use one of the system s standard estimators for many of your own operators These are the standard restriction estimators eqsel for negsel for lt gt scalarltsel for lt or lt scalargtsel for gt or gt It might seem a little odd that these are the categories but they make sense if you think about it will typically accept only a small fraction of the rows in a table lt gt will typically reject only a small fraction lt will accept a fraction that depends on where the given constant falls in the range of values for that table column which it just so happens is information collected by ANALYZE and made available to the selectivity estimator lt will accept a slightly larger fraction than lt for the same comparison constant but they re close enough to not be worth distinguishing especially since w
174. d procedural language so that only database superusers can create functions in it The writer of a PL TcIU function must take care that the function cannot be used to do anything unwanted since it will be able to do anything that could be done by a user logged in as the database administrator The shared object for the PL Tcl and PL TclU call handlers is automatically built and installed in the PostgreSQL library directory if Tcl Tk support is specified in the configuration step of the installation procedure To install PL Tcl and or PL TclU in a particular database use the createlang script for example createlang pltcl dbname Orcreatelang pltclu dbname 20 2 Description 20 2 1 PL Tcl Functions and Arguments To create a function in the PL Tcl language use the standard syntax CREATE FUNCTION funcname argument types RETURNS return type AS 4 PL Tcl function body LANGUAGE pltcl PL TclU is the same except that the language should be specified as pltclu The body of the function is simply a piece of Tcl script When the function is called the argument values are passed as variables 1 n to the Tcl script The result is returned from the Tcl code in the usual 345 Chapter 20 PL Tcl Tcl Procedural Language way with a return statement For example a function returning the greater of two integer values could be defined as CREATE FUNCTION tcl max integer integer RETURNS integer AS if
175. d set FOR loops and dynamic record set FOR loops FOUND is only set when the FOR loop exits inside the execution of the loop FOUND is not modified by the FOR statement although it may be changed by the execution of other statements within the loop body FOUND is a local variable any changes to it affect only the current PL pgSQL function 19 6 Control Structures Control structures are probably the most useful and important part of PL pgSQL With PL pgSQL s control structures you can manipulate PostgreSQL data in a very flexible and powerful way 19 6 1 Returning from a function RETURN expression RETURN with an expression is used to return from a PL pgSQL function that does not return a set The function terminates and the value of expression is returned to the caller To return a composite row value you must write a record or row variable as the expression When returning a scalar type any expression can be used The expression s result will be automatically cast into the function s return type as described for assignments If you have declared the function to return void then the expression can be omitted and will be ignored in any case The return value of a function cannot be left undefined If control reaches the end of the top level block of the function without hitting a RETURN statement a run time error will occur When a PL pgSQL function is declared to return SETOF somet ype the procedure to follow is sli
176. d twice with different names 13 3 4 1 Benefits The benefit of implementing views with the rule system is that the planner has all the information about which tables have to be scanned plus the relationships between these tables plus the restrictive qualifi cations from the views plus the qualifications from the original query in one single parse tree And this is still the situation when the original query is already a join over views Now the planner has to decide which is the best path to execute the query The more information the planner has the better this decision can be And the rule system as implemented in PostgreSQL ensures that this is all information available about the query up to now 226 Chapter 13 The Rule System 13 3 5 What about updating a view What happens if a view is named as the target relation for an INSERT UPDATE or DELETE After doing the substitutions described above we will have a query tree in which the result relation points at a subquery range table entry This will not work so the rewriter throws an error if it sees it has produced such a thing To change this we can define rules that modify the behavior of non SELECT queries This is the topic of the next section 13 4 Rules on INSERT UPDATE and DELETE 13 4 1 Differences from View Rules Rules that are defined ON INSERT UPDATE and DELETE are totally different from the view rules described in the previous section First their CREATE RULE
177. d via JavaBean properties so there are get and set methods for each of these proper ties Table 5 2 ConnectionPoolDataSource Configuration Properties Property Type Description serverName String PostgreSQL database server hostname databaseName String PostgreSQL database name portNumber int TCP IP port which the PostgreSQL database server is listening on or 0 to use the default port user String User used to make database connections 108 Chapter 5 JDBC Interface Property Type Description password String Password used to make database connections defaultAutoCommit boolean Whether connections should have autoCommit enabled or disabled when they are supplied to the caller The default is a1se to disable autoCommit Many application servers use a properties style syntax to configure these properties so it would not be unusual to enter properties as a block of text Example 5 5 ConnectionPoolDataSource Configuration Example If the application server provides a single area to enter all the properties they might be listed like this serverName localhost databaseName test user testuser password testpassword Or separated by semicolons instead of newlines like this serverName localhost databaseName test user testuser password testpassword 5 9 4 Applications DataSource PostgreSQL includes two implementations of DataSource for JDBC 2 and two f
178. dded SQL program consists of code written in an ordinary programming language in this case C mixed with SQL commands in specially marked sections To build the program the source code is first passed to the embedded SQL preprocessor which converts it to an ordinary C program and afterwards it can be processed by a C compilation tool chain Embedded SQL has advantages over other methods for handling SQL commands from C code First it takes care of the tedious passing of information to and from variables in your C program Secondly embedded SQL in C is defined in the SQL standard and supported by many other SQL databases The PostgreSQL implementation is designed to match this standard as much as possible and it is usually possible to port embedded SQL programs written for other RDBMS to PostgreSQL with relative ease As indicated programs written for the embedded SQL interface are normal C programs with special code inserted to perform database related actions This special code always has the form EXEC SO sec These statements syntactically take the place of a C statement Depending on the particular statement they may appear in the global context or within a function Embedded SQL statements follow the case sensitivity rules of normal SQL code and not those of C The following sections explain all the embedded SQL statements 4 2 Connecting to the Database Server One connects to a database using the following statement
179. dentifiers 1 2 etc Optionally aliases can be declared for n parameter names for increased readability Either the alias or the numeric identifier can then be used to refer to the parameter value Some examples CREATE FUNCTION sales tax REAL RETURNS REAL AS 311 Chapter 19 PL pgSQL SQL Procedural Language DECLARE subtotal ALIAS FOR 1 BEGIN return subtotal 0 06 D Bl ANGUAGE plpgsql CREATE FUNCTION instr VARCHAR INTEGER DECLARE v string ALIAS FOR 1 index ALIAS FOR 2 EGIN Some computations here D ANGUAGE plpgsql vs ETURNS INTEGER AS UJ amp CREATE FUNCTION use many fields tablename RETURNS TEXT AS DECLARE in t ALIAS FOR 1 BEGIN RETURN in t f1 in t f 3 in t f5 in t f7 END LANGUAGE plpgsql 19 3 2 Row Types name tablename ROWTYPE A variable of a composite type is called a row variable or row type variable Such a variable can hold a whole row of a SELECT or FOR query result so long as that query s column set matches the declared type of the variable The individual fields of the row value are accessed using the usual dot notation for example rowvar field Presently a row variable can only be declared using the ROWTYPE notation although one might expect a bare table name to work as a ty
180. dinary SQL command Subsequently arrival of NOTIFY messages can be detected by calling POnotifies POnotifies Returns the next notification from a list of unhandled notification messages received from the backend Returns NULL if there are no pending notifications Once a notification is returned from PQnotifies it is considered handled and will be removed from the list of notifications PGnotify PQnotifies PGconn conn typedef struct pgNotify char relname name of relation containing data int be pid process id of backend PGnotify After processing a PGnot ify object returned by POnotifies be sure to free it with free to avoid a memory leak Note In PostgreSQL 6 4 and later the be pia is that of the notifying backend whereas in earlier versions it was always the PID of your own backend The second sample program gives an example of the use of asynchronous notification POnotifies does not actually read backend data it just returns messages previously absorbed by an other libpq function In prior releases of libpq the only way to ensure timely receipt of NOTIFY messages was to constantly submit queries even empty ones and then check POnot ifies after each POexec While this still works it is deprecated as a waste of processing power A better way to check for NOTIFY messages when you have no useful queries to make is to call Pocon sumeInput then check PQnotifies You can use select
181. dispose of the structure and any associated memory blocks This must be done even if a call to POconnect Start or PQconnectPo11 failed POconnectPoll will currently block if libpq is compiled with USE_SSL defined This restriction may be removed in the future These functions leave the socket in a nonblocking state as if PQsetnonblocking had been called PQconndefaults Returns the default connection options POconninfoOption POconndefaults void struct POconninfoOption char char char char char char int keyword envvar compiled val label dispchar dispsize The keyword of the option Fallback environment variable name Fallback compiled in default value Option s current value or NULL Label for field in connect dialog Character to display for this field in a connect dialog Values are mm Display entered value as is meen Password field hide valu Dp Debug option don t show by default Field size in characters for dialog Returns a connection options array This may be used to determine all possible PQconnect db options and their current default values The return value points to an array of POconninfoOption structs which ends with an entry having a NULL keyword pointer Note that the default values va1 fields will depend on environment variables and other context Callers must treat the connection options data as read only Afte
182. dler and prevents it from being called directly in queries Note In PostgreSQL 7 1 and later call handlers must adhere to the version 1 function manager interface not the old style interface The call handler is called in the same way as any other function It receives a pointer to a Function CallInfoData struct containing argument values and information about the called function and it is expected to return a Datum result and possibly set the isnu11 field of the FunctionCallInfoData structure if it wishes to return an SQL NULL result The difference between a call handler and an or dinary callee function is that the 1info fn oid field of the FunctionCallInfoData structure will contain the OID of the actual function to be called not of the call handler itself The call handler must use this field to determine which function to execute Also the passed argument list has been set up according to the declaration of the target function not of the call handler It s up to the call handler to fetch the pg proc entry and to analyze the argument and return types of the called procedure The AS clause from the CREATE FUNCTION of the procedure will be found in the prosrc attribute of the pg proc table entry This may be the source text in the procedural language itself like for PL Tcl a path name to a file or anything else that tells the call handler what to do in detail Often the same function is called many times per SQL
183. e re not likely to do better than a rough guess anyhow Similar remarks apply to gt and gt You can frequently get away with using either eqse1 or neqsel for operators that have very high or very low selectivity even if they aren t really equality or inequality For example the approximate equality geometric operators use eqsel1 on the assumption that they ll usually only match a small fraction of the entries in a table 211 Chapter 11 Extending SQL Operators You can use scalarltsel and scalargtsel for comparisons on data types that have some sensible means of being converted into numeric scalars for range comparisons If possible add the data type to those understood by the routine convert to scalar in src backend utils adt selfuncs c Eventually this routine should be replaced by per data type functions identified through a column of the pg type system catalog but that hasn t happened yet If you do not do this things will still work but the optimizer s estimates won t be as good as they could be There are additional selectivity functions designed for geometric operators in src backend utils adt geo selfuncs c areasel positionsel and contsel At this writing these are just stubs but you may want to use them or even better improve them anyway 11 3 4 JOIN The JOTN clause if provided names a join selectivity estimation function for the operator note that this is a function name not an operator name JOIN
184. e The expression must yield a single value If the expression s result data type doesn t match the variable s data type or the variable has a specific size precision like char 20 the result value will be implicitly converted by the PL pgSQL interpreter using the result type s output function and the variable type s input function Note that this could poten tially result in run time errors generated by the input function if the string form of the result value is not acceptable to the input function Examples user id 20 tax subtotal 0 06 19 5 2 SELECT INTO The result of a SELECT command yielding multiple columns but only one row can be assigned to a record variable row type variable or list of scalar variables This is done by SELECT INTO target expressions FROM where target can be a record variable a row variable or a comma separated list of simple variables and record row fields Note that this is quite different from PostgreSQL s normal interpretation of SELECT INTO which is that the INTO target is a newly created table If you want to create a table from a SELECT result inside a PL pgSQL function use the syntax CREATE TABLE AS SELECT If a row or a variable list is used as target the selected values must exactly match the structure of the target s or a run time error occurs When a record variable is the target it automatically configures itself to the row type of
185. e We chose a new name PostgreSQL to reflect the relationship between the original POSTGRES and the more recent ver sions with SQL capability At the same time we set the version numbering to start at 6 0 putting the numbers back into the sequence originally begun by the Berkeley POSTGRES project The emphasis during development of Postgres95 was on identifying and understanding existing problems in the backend code With PostgreSQL the emphasis has shifted to augmenting features and capabilities although work continues in all areas Major enhancements in PostgreSQL include Table level locking has been replaced by multiversion concurrency control which allows readers to continue reading consistent data during writer activity and enables hot backups from pg dump while the database stays available for queries Important backend features including subselects defaults constraints and triggers have been imple mented Additional SQL92 compliant language features have been added including primary keys quoted iden tifiers literal string type coercion type casting and binary and hexadecimal integer input Built in types have been improved including new wide range date time types and additional geometric type support Overall backend code speed has been increased by approximately 20 40 and backend start up time has decreased by 80 since version 6 0 was released iii Preface 3 What s In This Book This book is fo
186. e we d just name the aggregate sum and rely on PostgreSQL to figure out which kind of sum to apply to a column of type complex The above definition of sum will return zero the initial state condition if there are no non null input values Perhaps we want to return NULL in that case instead the SQL standard expects sum to behave that way We can do this simply by omitting the initcond phrase so that the initial state condition is NULL Ordinarily this would mean that the s func would need to check for a NULL state condition input but for sum and some other simple aggregates like max and min it s sufficient to insert the first non null input value into the state variable and then start applying the transition function at the second non null input value PostgreSQL will do that automatically if the initial condition is NULL and the transition function is marked strict i e not to be called for NULL inputs Another bit of default behavior for a strict transition function is that the previous state value is retained unchanged whenever a NULL input value is encountered Thus null values are ignored If you need some other behavior for NULL inputs just define your transition function as non strict and code it to test for NULL inputs and do whatever is needed Avg average is a more complex example of an aggregate It requires two pieces of running state the sum of the inputs and the count of the number of inputs The final result is
187. e Tcl break continue and return commands with the expected behavior Note that if the queryProcedure executes return pg execute does not return ntuples pg execute is a newer function which provides a superset of the features of pg select and can replace pg exec in many cases where access to the result handle is not needed For backend handled errors pg execute will throw a Tcl error and return two element list The first element is an error code such as PGRES FATAL ERROR and the second element is the backend error text For more serious errors such as failure to communicate with the backend pg execute will throw a Tcl error and return just the error message text Usage In the following examples error checking with catch has been omitted for clarity Insert a row and save the OID in result oid pg execut oid result oid Spgconn insert into mytable values 1 Print the item and value fields from each row pg execute array d Spgconn select item value from mytable puts Item Sd item Value d value Find the maximum and minimum values and store them in s max and s min pg execute array s pgconn select max value as max min value as min from mytable Find the maximum and minimum values and store them in max and min pg execute Spgconn select max value as max min value as min from mytable 53 pg listen Name pg listen setor change a callback for asynchronous NOTIFY mess
188. e different Tcl procedures too This is not normally a concern for a PL Tcl programmer but it might be visible when debugging 351 Chapter 21 PL Perl Perl Procedural Language PL Perl is a loadable procedural language that enables you to write PostgreSQL functions in the Perl programming language To install PL Perl in a particular database use createlang plperl dbname Tip If a language is installed into templatel all subsequently created databases will have the lan guage installed automatically Note Users of source packages must specially enable the build of PL Perl during the installation process refer to the installation instructions for more information Users of binary packages might find PL Perl in a separate subpackage 21 1 PL Perl Functions and Arguments To create a function in the PL Perl language use the standard syntax CREATE FUNCTION funcname argument types RETURNS return type AS PL Perl function body LANGUAGE plperl The body of the function is ordinary Perl code Arguments and results are handled as in any other Perl subroutine Arguments are passed in _ and a result value is returned with return or as the last expression evaluated in the function For example a function returning the greater of two integer values could be defined as CREATE FUNCTION perl max integer integer RETURNS integer AS if 0 gt 1 return 0 return 1 LAN
189. e for writing into The normal macros will sometimes return a pointer to a value that is physically stored in a table and so must not be written to Using the PG GETARG xxx COPY macros guarantees a writable result The second variant consists of the PG GETARG xxx SLICE macros which take three parameters The first is the number of the parameter as above The second and third are the offset and length of the segment to be returned Offsets are counted from zero and a negative length requests that the remainder of the value be returned These routines provide more efficient access to parts of large values in the case R TABLE tablename ALTER COLUMN colname SET STORAGE storagetype Storage type is one of Ln where they have storage type external The storage type of a column can be specified using ALTI plain external extended or main ee The version 1 function call conventions make it possible to return set results and implement trigger functions and procedural language call handlers Version 1 code is also more portable than version 0 because it does not break ANSI C restrictions on function call protocol For more details see src backend utils fmgr README in the source distribution 9 5 5 Composite Types in C Language Functions Composite types do not have a fixed layout like C structures Instances of a composite type may contain null fields In addition composite types
190. e function is called You may use the following macros to examine tg event TRIGGER FIRED BEFOREX tg event returns TRUE if trigger fired BEFORE TRIGGER FIRED AFTER tg event Returns TRUE if trigger fired AFTER TRIGGER FIRED FOR ROW event Returns TRUE if trigger fired for a ROW level event TRIGGER FIRED FOR STATEMENTV event Returns TRUE if trigger fired for STATEMENT level event TRIGGER FIRED BY INSERT event Returns TRUE if trigger fired by INSERT 254 Chapter 16 Triggers TRIGGER FIRED BY DELETE event Returns TRUE if trigger fired by DELETE TRIGGER FIRED BY UPDATE event Returns TRUE if trigger fired by UPDATE tg relation is a pointer to structure describing the triggered relation Look at utils rel h for details about this structure The most interesting things are tg relation rd att descriptor of the relation tuples and tg relation rd rel relname relation s name This is not char but NameData Use SPI getrelname tg relation to get char if you need a copy of the name tg trigtuple is a pointer to the tuple for which the trigger is fired This is the tuple being inserted if INSERT deleted if DELETE or updated 1f UPDATE If INSERT DELETE then this is what you are to return to Executor if you don t want to replace tuple with another one INSERT or skip the operation tg newtuple is a pointer to the new version of tuple if UPDATE and NULL if this is for an INSERT or a DELETE This is what
191. e given status PGresult PQmakeEmptyPGresult PGconn conn ExecStatusType status This is libpq s internal routine to allocate and initialize an empty PGresult object It is exported because some applications find it useful to generate result objects particularly objects with error status themselves If conn is not NULL and status indicates an error the connection s current error message is copied into the PGresult Note that PQclear should eventually be called on the object just as with PGresult returned by libpq itself 1 3 2 Escaping strings for inclusion in SQL queries PQescapeString Escapes a string for use within an SQL query size t PQescapeString char to const char from size t length If you want to include strings that have been received from a source that is not trustworthy for exam ple because a random user entered them you cannot directly include them in SQL queries for security reasons Instead you have to quote special characters that are otherwise interpreted by the SQL parser PQescapeString performs this operation The from points to the first character of the string that is to be escaped and the 2engt h parameter counts the number of characters in this string a terminating zero byte is neither necessary nor counted to shall point to a buffer that is able to hold at least one more character than twice the value of 1ength otherwise the behavior is undefined A call to PoescapeString writes an e
192. e included in this class also A number of additional DB class methods are described below The preferred way to use this module is as follows See description of the initialization method below import pg db pg DB for r in db query SELECT foo bar FROM foo_bar_table WHERE foo bar dictresult print foo s bar s r The following describes the methods and variables of this class The DB class is initialized with the same arguments as the pg connect method It also initializes a few internal variables The statement db DB will open the local database with the name of the user just like pg connect does pkey Name pkey return the primary key of a table Synopsis pkey table Parameters table name of table Return Type string Name of field which is the primary key of the table 140 pkey Description pkey method returns the primary key of a table Note that this raises an exception if the table does not have a primary key 141 get databases Name get databases get list of databases in the system Synopsis get databases Parameters none Return Type list List of databases in the system Description Although you can do this with a simple select it is added here for convenience 142 get tables Name get tables get list of tables in connected database Synopsis get tables Parameters none Retur
193. e input function takes a null terminated character string as its input and returns the internal in memory representation of the type The output function takes the internal representation of the type and returns a null terminated character string Suppose we want to define a complex type which represents complex numbers Naturally we would choose to represent a complex in memory as the following C structure typedef struct Complex double X double y Complex and a string of the form x y as the external string representation The functions are usually not hard to write especially the output function However there are a number of points to remember When defining your external string representation remember that you must eventually write a com plete and robust parser for that representation as your input function For instance Complex complex in char str double x y Complex result if sscanf str 1f 1f amp x amp y 2 elog ERROR complex in error in parsing s str return NULL result Complex palloc sizeof Complex result gt x x result gt y y return result The output function can simply be char complex_out Complex complex char result 206 Chapter 10 Extending SQL Types if complex NULL return NULL result char palloc 60 sprintf result g g complex gt x complex y return result You
194. e join tree nodes It turns out to be convenient to store the top level WHERE expression as a qualification attached to the top level join tree item too So really the join tree represents both the FROM and WHERE clauses of a SELECT the others The other parts of the query tree like the ORDER BY clause aren t of interest here The rule system substitutes entries there while applying rules but that doesn t have much to do with the fundamentals of the rule system 13 3 Views and the Rule System 13 3 1 Implementation of Views in PostgreSQL Views in PostgreSQL are implemented using the rule system In fact there is essentially no difference between CREATE VIEW myview AS SELECT FROM mytab compared against the two commands CREATE TABLE myview same attribute list as for mytab CREATE RULE RETURN AS ON SELECT TO myview DO INSTEAD SELECT FROM mytab because this is exactly what the CREATE VIEW command does internally This has some side effects One of them is that the information about a view in the PostgreSQL system catalogs is exactly the same as it is for a table So for the query parser there is absolutely no difference between a table and a view They are the same thing relations That is the important one for now 219 Chapter 13 The Rule System 13 3 2 How SELECT Rules Work Rules ON SELECT are applied to all queries as the last step e
195. e mailing lists are a good place to have your questions answered to share experiences with other users and to contact the developers Consult the User s Lounge section of the PostgreSQL web site for details Yourself PostgreSQL is an open source effort As such it depends on the user community for ongoing support As you begin to use PostgreSQL you will rely on others for help either through the documentation or through the mailing lists Consider contributing your knowledge back If you learn something which is not in the documentation write it up and contribute it If you add features to the code contribute them Even those without a lot of experience can provide corrections and minor changes in the documenta tion and that is a good way to start The lt pgsqi docs postgresql org gt mailing list is the place to get going 5 Terminology and Notation An administrator is generally a person who is in charge of installing and running the server A user could be anyone who is using or wants to use any part of the PostgreSQL system These terms should not be interpreted too narrowly this documentation set does not have fixed presumptions about system administration procedures We use usr 1local pgsql as the root directory of the installation and usr local pgsql data as the directory with the database files These directories may vary on your site details can be derived in the Administrator s Guide 5 http www postgre
196. e on Man agement of Data May 1986 M Stonebraker E Hanson and C H Hong The design of the POSTGRES rules system Proc IEEE Conference on Data Engineering Feb 1987 M Stonebraker The design of the POSTGRES storage system Proc VLDB Conference Sept 1987 M Stonebraker M Hearst and S Potamianos A commentary on the POSTGRES rules system SIG MOD Record 18 3 Sept 1989 M Stonebraker The case for partial indexes SIGMOD Record 18 4 Dec 1989 p 4 11 M Stonebraker L A Rowe and M Hirohama The implementation of POSTGRES Transactions on Knowledge and Data Engineering 2 1 IEEE March 1990 M Stonebraker A Jhingran J Goh and S Potamianos On Rules Procedures Caching and Views in Database Systems Proc ACM SIGMOD Conference on Management of Data June 1990 E http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M87 13 pdf http simon cs cornell edu home praveen papers partindex de95 ps Z http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M85 95 pdf http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M87 06 pdf http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M89 82 pdf http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M89 17 pdf http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M90 34 pdf 0 http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M90 36 pdf 360 Index Symbols libdir aggregate aggregate functions
197. e operation for the current tuple and so the tuple will not be in serted updated deleted For INSERT and UPDATE triggers only the returned tuple becomes the tuple which will be inserted or will replace the tuple being updated This allows the trigger function to modify the row being inserted or updated A BEFORE trigger that does not intend to cause either of these behaviors must be careful to return the same NEW tuple it is passed Note that there is no initialization performed by the CREATE TRIGGER handler This may be changed in the future If more than one trigger is defined for the same event on the same relation the triggers will be fired in alphabetical order by name In the case of BEFORE triggers the possibly modified tuple returned by each trigger becomes the input to the next trigger If any BEFORE trigger returns NULL the operation is abandoned and subsequent triggers are not fired If a trigger function executes SQL queries using SPI then these queries may fire triggers again This is known as cascading triggers There is no direct limitation on the number of cascade levels It is possible for cascades to cause recursive invocation of the same trigger for example an INSERT trigger might execute a query that inserts an additional tuple into the same table causing the INSERT trigger to be fired again It is the trigger programmer s responsibility to avoid infinite recursion in such scenarios 16 2 Interaction with the
198. e query then the originally given query will be executed and its command status will be returned as usual But note that if there were any conditional INSTEAD rules the negation of their qualifications will have been added to the original query This may reduce the number of rows it processes and if so the reported status will be affected n If there is any unconditional INSTEAD rule for the query then the original query will not be executed at all In this case the server will return the command status for the last query that was inserted by an INSTEAD rule conditional or unconditional and is of the same type INSERT UPDATE or DELETE as the original query If no query meeting those requirements is added by any rule then the returned command status shows the original query type and zeroes for the tuple count and OID fields The programmer can ensure that any desired INSTEAD rule is the one that sets the command status in the second case by giving it the alphabetically last rule name among the active rules so that it fires last 13 7 Rules versus Triggers Many things that can be done using triggers can also be implemented using the PostgreSQL rule system What currently cannot be implemented by rules are some kinds of constraints It is possible to place a qualified rule that rewrites a query to NOTHING if the value of a column does not appear in another table But then the data is silently thrown away and that s not a good idea If
199. e size of a data page is 8192 bytes the default which can be raised up to 32768 the upper limit on the size of a data value was relatively low To support the storage of larger atomic values PostgreSQL provided and continues to provide a large object interface This interface provides file oriented access to user data that has been declared to be a large object POSTGRES 4 2 the indirect predecessor of PostgreSQL supported three standard implementations of large objects as files external to the POSTGRES server as external files managed by the POSTGRES server and as data stored within the POSTGRES database This caused considerable confusion among users As a result only support for large objects as data stored within the database is retained in Post greSQL Even though this is slower to access it provides stricter data integrity For historical reasons this storage scheme is referred to as Inversion large objects You will see the term Inversion used occasionally to mean the same thing as large object Since PostgreSQL 7 1 all large objects are placed in one system table called pg 1argeobject PostgreSQL 7 1 introduced a mechanism nicknamed TOAST that allows data rows to be much larger than individual data pages This makes the large object interface partially obsolete One remaining advan tage of the large object interface is that it allows random access to the data i e the ability to read or write small chunks of a large value It
200. e the ap propriate steps to return the input text enclosed in single or double quotes and with any embedded special characters properly escaped Here is a much larger example of a dynamic query and EXECUTE CREATE FUNCTION cs update referrer type proc RETURNS INTEGER AS DECLARE referrer keys RECORD Declare a generic record to be used in a FOR a output varchar 4000 BEGIN a output CREATE FUNCTION cs find referrer type varchar varchar varchar RETURNS VARCHAR AS DECLARE v host ALIAS FOR 1 v domain ALIAS FOR 2 318 Notice how w Chapter 19 PL pgSQL SQL Procedural Language v url ALIAS FOR 3 BEGIN Scan through the results of a query in a FOR loop using the FOR record construct FOR referrer keys IN SELECT FROM cs referrer keys ORDER BY try order LOOP a output a output IF v referrer keys kind LIKE referrer keys key string THEN RETURN referrer keys referrer typ ee END SLB gs END LOOP a output a output RETURN NULL END LANGUAGE plpgsql This works because we are not substituting any variables Otherwise it would fail Look at PERFORM for another way to run functions EXECUTE a output LANGUAGE plpgsql 19 5 5 Obtaining result status There are several ways to determ
201. eTableSlot slot OPTIONAL pointer to misc user provided context info user fctx is for use as a pointer to your own struct to retain arbitrary context information between calls for your function xy void user fctx OPTIONAL pointer to struct containing arrays of attribute type input metainfo attinmeta is for use when returning tuples i e composite data types and is not needed when returning base i e scalar data types It is ONLY needed if you intend to use BuildTupleFromCStrings to create the return tuple xf AttInMetadata attinmeta 194 Chapter 9 Extending SQL Functions memory context used for structures which must live for multiple calls multi call memory ctx is set by SRF FIRSTCALL INIT for you and used by SREF RETURN DONE for cleanup It is the most appropriate memory context for any memory that is to be re used across multiple calls of the SRF QUA MemoryContext multi call memory ctx FuncCallContext An SRE uses several functions and macros that automatically manipulate the FuncCallContext struc ture and expect to find it via n extra Use SRF IS FIRSTCALL to determine if your function is being called for the first or a subsequent time On the first call only use SRF FIRSTCALL INIT to initialize the FuncCallContext On every function call including the first use SRF PERCALL SETUP to properly set up for using the FuncCa
202. each entry to the FOR loop This allows the programmer to choose the speed of a pre planned query or the flexibility of a dynamic query just as with a plain EXECUTE statement Note The PL pgSQL parser presently distinguishes the two kinds of FOR loops integer or record returning by checking whether the target variable mentioned just after FOR has been declared as a record row variable If not it s presumed to be an integer FOR loop This can cause rather nonintuitive error messages when the true problem is say that one has misspelled the FOR variable name 19 7 Cursors Rather than executing a whole query at once it is possible to set up a cursor that encapsulates the query and then read the query result a few rows at a time One reason for doing this is to avoid memory overrun when the result contains a large number of rows However PL pgSQL users don t normally need to worry about that since FOR loops automatically use a cursor internally to avoid memory problems A more interesting usage is to return a reference to a cursor that it has created allowing the caller to read the rows This provides an efficient way to return large row sets from functions 19 7 1 Declaring Cursor Variables All access to cursors in PL pgSQL goes through cursor variables which are always of the special data type refcursor One way to create a cursor variable is just to declare it as a variable of type refcursor Another way is to use the cursor declar
203. eatelang may be used instead of carrying out the details by hand For example to install PL pgSQL into the templatel database use createlang plpgsql templatel The manual procedure described below is only recommended for installing custom languages that cre atelang does not know about Manual Procedural Language Installation A procedural language is installed in the database in three steps which must be carried out by a database superuser 1 The shared object for the language handler must be compiled and installed into an appropriate library directory This works in the same way as building and installing modules with regular user defined C functions does see Section 9 5 8 2 The handler must be declared with the command CREATE FUNCTION handler function name RETURNS LANGUAGE HANDLER AS path to shared object LANGUAGE C The special return type of LANGUAGE HANDLER tells the database that this function does not return one of the defined SQL data types and is not directly usable in SQL statements 305 Chapter 18 Procedural Languages 3 The PL must be declared with the command CREATE TRUSTED PROCEDURAL LANGUAGE language name HANDLER handler function name The optional key word TRUSTED tells whether ordinary database users that have no superuser privi leges should be allowed to use this language to create functions and trigger procedures Since PL func
204. ected set result is int to l otherwise set it to 0 Setting result is int to tells libpq to byte swap the value if necessary so that it is delivered as a proper int value for the client machine When result is int is 0 the byte string sent by the backend is returned unmodified args and nargs specify the arguments to be passed to the function typedef struct int len int isint union znt per int integer u PQArgBlock POfn always returns a valid PGresult The result status should be checked before the result is used The caller is responsible for freeing the PGresult with PQclear when it is no longer needed 1 6 Asynchronous Notification PostgreSQL supports asynchronous notification via the LISTEN and NOTIFY commands A backend reg isters its interest in a particular notification condition with the LISTEN command and can stop listening 16 Chapter 1 libpq C Library with the UNLISTEN command All backends listening on a particular condition will be notified asyn chronously when a NOTIFY of that condition name is executed by any backend No additional information is passed from the notifier to the listener Thus typically any actual data that needs to be communicated is transferred through a database relation Commonly the condition name is the same as the associated relation but it is not necessary for there to be any associated relation libpq applications submit LISTEN and UNLISTEN commands as or
205. ection can also be found in uncs sq1 and funcs c in the tutorial directory Throughout this chapter it can be useful to look at the reference page ofthe CREATE FUNCTION command to understand the examples better 9 2 Query Language SQL Functions SQL functions execute an arbitrary list of SQL statements returning the result of the last query in the list which must be a SELECT In the simple non set case the first row of the last query s result will be returned Bear in mind that the first row of a multirow result is not well defined unless you use ORDER BY If the last query happens to return no rows at all NULL will be returned Alternatively an SQL function may be declared to return a set by specifying the function s return type as SETOF somet ype In this case all rows of the last query s result are returned Further details appear below The body of an SQL function should be a list of one or more SQL statements separated by semicolons Note that because the syntax of the CREATE FUNCTION command requires the body of the function to be enclosed in single quotes single quote marks used in the body of the function must be escaped by writing two single quotes or a backslash where each quote is desired Arguments to the SQL function may be referenced in the function body using the syntax n 1 refers to the first argument 2 to the second and so on If an argument is of a composite ty
206. ecute is similar to the executeQuery used to issue a select however it doesn t return a result Example 5 3 Drop Table Example This example will drop a table Statement st db createStatement ResultSet rs st executeQuery DROP TABLE mytable st close 5 6 Storing Binary Data PostgreSQL provides two distinct ways to store binary data Binary data can be stored in a table using PostgreSQL s binary data type bytea or by using the Large Object feature which stores the binary data in a separate table in a special format and refers to that table by storing a value of type OID in your table In order to determine which method is appropriate you need to understand the limitations of each method The bytea data type is not well suited for storing very large amounts of binary data While a column of type bytea can hold up to 1 GB of binary data it would require a huge amount of memory RAM to process such a large value The Large Object method for storing binary data is better suited to storing very large values but it has its own limitations Specifically deleting a row that contains a Large Object does not delete the Large Object Deleting the Large Object is a separate operation that needs to be performed Large Objects also have some security issues since anyone connected to the database case view and or modify any Large Object even if they don t have permissions to view update the row containing the Large Object
207. ed any longer the whole transaction gets aborted and the system jumps back into the main loop to get the next query from the client application It is possible to hook into the error mechanism to notice that this happens But currently it is impossible to tell what really caused the abort input output conversion error floating point error parse error And it is possible that the database backend is in an inconsistent state at this point so returning to the upper executor or issuing more commands might corrupt the whole database Thus the only thing PL pgSQL currently does when it encounters an abort during execution of a function or trigger procedure is to write some additional NOTICE level log messages telling in which function and where line number and type of statement this happened The error always stops execution of the function 19 9 Trigger Procedures PL pgSQL can be used to define trigger procedures A trigger procedure is created with the CREATE FUNCTION command as a function with no arguments and a return type of TRIGGER Note that the function must be declared with no arguments even if it expects to receive arguments specified in CREATE TRIGGER trigger arguments are passed via TG ARGV as described below When a PL pgSQL function is called as a trigger several special variables are created automatically in the top level block They are NEW Data type RECORD variable holding the new
208. educe the total amount of time required to parse and generate query plans for the statements in a procedural language function A disadvantage is that errors in a specific expression or query may not be detected until that part of the function is reached in execution Once PL pgSQL has made a query plan for a particular query in a function it will re use that plan for the life of the database connection This is usually a win for performance but it can cause some problems if you dynamically alter your database schema For example CREATE FUNCTION populate RETURNS INTEGER AS DECLARE Declarations BEGIN PERFORM my function END LANGUAGE plpgsql 307 Chapter 19 PL pgSQL SQL Procedural Language If you execute the above function it will reference the OID for my_function in the query plan pro duced for the PERFORM statement Later if you drop and re create my function then populate will not be able to find my_function anymore You would then have to re create populate or at least start a new database session so that it will be compiled afresh Because PL pgSQL saves execution plans in this way queries that appear directly in a PL pgSQL function must refer to the same tables and fields on every execution that is you cannot use a parameter as the name of a table or field in a query To get around this restriction you can construct dynamic queries using the P
209. el FROM shoelace data 6 S hoelace data sl name sl7 UPDATE shoelace data SET sl avail 6 WHERE sl name sl7 These are executed in this order and that is exactly what the rule defines The substitutions and the quali fications added ensure that if the original query would be say UPDATE shoelace data SET sl color green WHERE sl name sl7 no log entry would get written This time the original parse tree does not contain a target list entry for s avail so NEW sl avail will get replaced by shoelace data sl avail resulting in the extra query INSERT INTO shoelace log VALUES shoelace data sl name shoelace data sl avail current user current timestamp FROM shoelace data WHERE shoelace data sl avail shoelace data sl avail AND shoelace data sl name sl7 and that qualification will never be true It will also work if the original query modifies multiple rows So if Al would issue the command UPDATE shoelace data SET sl avail 0 WHERE sl color black four rows in fact get updated s11 s12 s13 and s14 But s13 already has sl avail 0 This time the original parse trees qualification is different and that results in the extra parse tree INSERT INTO shoelace log SELECT shoelace data sl name O0 current user current timestamp FROM shoelace data WHERE 0 shoelace data sl avail AND shoelace data sl color
210. en sent to the backend using POputline or when the last string has been received from the backend using PGget line It must be issued or the backend may get out of sync with the frontend Upon return from this function the backend is ready to receive the next SQL command The return value is 0 on successful completion nonzero otherwise int PQendcopy PGconn conn As an example PQexec conn CREATE TABLE foo a int4 b char 16 d double precision PQexec conn COPY foo FROM STDIN PQputline conn 3 thello world t4 5 n PQput line conn 4 tgoodbye world t7 11 n PQputline conn n PQendcopy conn When using POgetResult the application should respond to a PGRES COPY OUT result by executing PQgetline repeatedly followed by PQendcopy after the terminator line is seen It should then return to the PQgetResult loop until PogetResult returns NULL Similarly a PGRES COPY IN result is processed by a series of POputline calls followed by PQendcopy then return to the POgetResult loop This arrangement will ensure that a copy in or copy out command embedded in a series of SQL commands will be executed correctly Older applications are likely to submit a copy in or copy out via PQexec and assume that the transaction is done after PQendcopy This will work correctly only if the copy in out is the only SQL command in the command string 1 8 libpq Tracing Functions PQtrace Enable tracing of t
211. ents lte E E si iestesS re R eb esa Ves EPLUR S PL pe PVPR SENE SEVERE VUAUR FeN UR EL URS PLUR EE TOR GE N A E E i 1 Whats PostgreSQL hetero bei dpt tiefen te ridet eene 1 2 A Short History of PostgreSQL rennin n E EE E nennen nene en nennen neeneeen nennen nennen i 2A The Be rkeley POSTGRES Projects aen ete rete td eei terrier ii 2 2 POStgT6802 o de er A A e A S E E ERST ii PASS ue iru1N10 bl pne i e ESEE o ER ERENNERT ESEN ES iii 3 What s In This BOOK terret pe iD Ee tere ipee rp e i Pee iv 4 Overview of Documentation ReSOUPCES ceeceececsecenseceecesecesseceecessecesseeeeeeseecsaeeeaeceseeeaeeeeeeens iv 5 Terminology and Notation ienero oreren i ee EE E R A TEE i ai v 6 Bug Reporting Guidelines ei Neier nrnna a e o e a vi 6 1 Identifymg Bugs tree e eemper a an i n a a eee vi 6 2 What tore porti ain rE A R EETA EE AE RA vii 6 3 Where to report DUGS nieis entere E E E T E E A EE viii I Client n 1 T dibpq s C ibrary uo mer e ee E E ee eere e EER EE 1 T T Introduction nior rd e EUR REMO DR er 1 1 2 Database Connection Functions essere nene nennen neret nente enne 1 1 3 Command Execution Functions esses eeeee nennen nente nennen tenen nennen enne 7 1 3 1 Mam ROUUNES oec ES SEEN E ERR EE REIR REUNIR aie 8 1 3 2 Escaping strings for inclusion in SQL queries esse 9 1 3 3 Escaping binary strings for inclusion
212. er dbName getenv USER change this to the name of your test database make a connection to the database conn PQsetdb pghost pgport pgoptions pgtty dbName check to see that the backend connection was successfully made y if PQstatus conn CONNECTION_BAD fprintf stderr Connection to database s failed n dbName fprintf stderr Ss PQerrorMessage conn exit nicely conn res PQexec conn LISTEN TBL2 if res PQresultStatus res PGRES COMMAND OK fprintf stderr LISTEN command failedWn 27 Chapter 1 libpq C Library POclear res exit nicely conn should PQclear PGresult whenever it is no longer needed to avoid memory leaks Af PQclear res while 1 wait a little bit between checks waiting with select would be mor fficient p sleep 1 collect any asynchronous backend messages POconsumeInput conn check for asynchronous notify messages while notify POnotifies conn NULL fprintf stderr ASYNC NOTIFY of s from backend pid d received n notify relname notify be pid free notify close the connection to the database and cleanup POfinish conn return 0 Example 1 3 libpq Example Program 3 testlibpq3 c Test the C version of Libpq the PostgreSQL frontend library tests the binary cursor interface populate a database by doing the following
213. er example is that the floating point data types are unsafe for hash joins On machines that meet the IEEE floating point standard minus zero and plus zero are different values different bit patterns but they are defined to compare equal So if the equality operator on floating point data types were marked HASHES a minus zero and a plus zero would probably not be matched up by a hash join but they would be matched up by any other join process The bottom line is that you should probably only use HASHES for equality operators that are or could be implemented by memcmp 11 3 6 MERGES SORT1 SORT2 LTCMP GTCMP The MERGES clause if present tells the system that it is permissible to use the merge join method for a join based on this operator MERGES only makes sense for binary operators that return boolean and in practice the operator must represent equality for some data type or pair of data types Merge join is based on the idea of sorting the left and right hand tables into order and then scanning them in parallel So both data types must be capable of being fully ordered and the join operator must be one that can only succeed for pairs of values that fall at the same place in the sort order In practice this means that the join operator must behave like equality But unlike hash join where the left and right data types had better be the same or at least bitwise equivalent it is possible to me
214. er strings threads with libpq 22 tid time constants current data type output format See Also Formatting time with time zone data type time without time zone time time zone time zones timeout authentication deadlock timestamp data type timestamp with time zone data type timestamp without time zone data type timezone conversion 366 Index TOAST and user defined types transaction ID wraparound transaction isolation level transactions trigger triggers in PL Tcl Tru64 UNIX true types See data types union UnixWare unqualified names UPDATE upgrading user current vacuum variance version view views updating 226 void where xid yacc 367
215. ernal name and the local name is GD It is recommended that GD be used for private status data of a procedure Use regular Tcl global variables only for values that you specifically intend to be shared among multiple procedures An example of using GD appears in the spi execp example below 20 2 4 Database Access from PL Tcl The following commands are available to access the database from the body of a PL Tcl procedure Spi exec count n array name query loop body Execute an SQL query given as a string An error in the query causes an error to be raised Other wise the command s return value is the number of rows processed selected inserted updated or deleted by the query or zero if the query is a utility statement In addition if the query is a SELECT statement the values of the selected columns are placed in Tcl variables as described below The optional count value tells spi exec the maximum number of rows to process in the query The effect of this is comparable to setting up the query as a cursor and then saying FETCH n If the query is a SELECT statement the values of the statement s result columns are placed into Tcl variables named after the columns If the array option is given the column values are instead stored into the named associative array with the SELECT column names used as array indexes If the query is a SELECT statement and no 1oop body script is given then only the first row of re
216. erty Type Description ServerName String PostgreSQL database server hostname databaseName String PostgreSQL database name portNumber int TCP IP port which the PostgreSQL database server is listening on or 0 to use the default port user String User used to make database connections password String Password used to make database connections The pooling implementations require some additional configuration properties Table 5 5 Additional Pooling DataSource Configuration Properties Property Type Description dataSourceName String Every pooling DataSource must have a unique name initialConnections int The number of database connections to be created when the pool is initialized maxConnections int The maximum number of open database connections to allow When more connections are requested the caller will hang until a connection is returned to the pool Here s an example of typical application code using a pooling DataSource Example 5 6 DataSource Code Example Code to initialize a pooling DataSource might look like this Jdbc3PoolingDataSource source new Jdbc3PoolingDataSource source setDataSourceName A Data Source 110 PoolingDataSo Chapter 5 JDBC Interface source setServerName localhost source setDatabaseName test source setUser testuser source setPassword testpassword source setMaxConnections 10 Then code to use a connectio
217. es of the argument types must be given as a Tcl list Write an empty list for typelist if no arguments are used Presently the argument types must be identified by the internal type names shown in pg type for example int4 not integer The return value from spi prepare is a query ID to be used in subsequent calls to spi execp See spi execp for an example Spi execp count n array name nulls string queryid value list loop body Execute a query previously prepared with spi prepare queryid is the ID returned by spi prepare If the query references arguments a value list must be supplied this is a Tcl list of actual values for the arguments This must be the same length as the argument type list previously given to spi prepare Omit value list if the query has no arguments The optional value for nu11s is a string of spaces and n characters telling spi execp which of the arguments are null values If given it must have exactly the same length as the va1ue 1ist lf it is not given all the argument values are non NULL Except for the way in which the query and its arguments are specified spi execp works just like spi exec The count array and 100p body options are the same and so is the result value Here s an example of a PL Tcl function using a prepared plan CREATE FUNCTION tl_count integer integer RETURNS integer AS if info exists GD plan f prepare the saved plan on the fi
218. es only one additional Perl command elog level msg Emit a log or error message Possible levels are DEBUG LOG INFO NOTICE WARNING and ERROR ERROR raises an error condition further execution of the function is abandoned and the current transaction is aborted 21 4 Trusted and Untrusted PL Perl Normally PL Perl is installed as a trusted programming language named pl1per1 In this setup certain Perl operations are disabled to preserve security In general the operations that are restricted are those that interact with the environment This includes file handle operations require and use for external modules There is no way to access internals of the database backend process or to gain OS level access with the permissions of the PostgreSQL user ID as a C function can do Thus any unprivileged database user may be permitted to use this language Here is an example of a function that will not work because file system operations are not allowed for security reasons CREATE FUNCTION badfunc RETURNS integer AS open TEMP tmp badfile print TEMP Gotcha n return 1 LANGUAGE plperl The creation of the function will succeed but executing it will not Sometimes it is desirable to write Perl functions that are not restricted for example one might want a Perl function that sends mail To handle these cases PL Perl can also be installed as an untrusted language
219. es should be provided whenever appropriate because they can make for considerable speedups in execution of queries that use the operator But if you provide them you must be sure that they are right Incorrect use of an optimization clause can result in backend crashes subtly wrong output or other Bad Things You can always leave out an optimization clause if you are not sure about it the only consequence is that queries might run slower than they need to Additional optimization clauses might be added in future versions of PostgreSQL The ones described here are all the ones that release 7 3 2 understands 11 3 1 COMMUTATOR The COMMUTATOR clause if provided names an operator that is the commutator of the operator being defined We say that operator A is the commutator of operator B if x A y equals y B x for all possible input values x y Notice that B is also the commutator of A For example operators and gt for a particular data type are usually each others commutators and operator is usually commutative with itself But operator is usually not commutative with anything The left operand type of a commuted operator is the same as the right operand type of its commutator and vice versa So the name of the commutator operator is all that PostgreSQL needs to be given to look up the commutator and that s all that needs to be provided in the COMMUTATOR clause When you are defining a self commutative operator you just do
220. essful an object handling a database connection is returned Exceptions TypeError Bad argument type or too many arguments SyntaxError Duplicate argument definition pg error Some error occurred during pg connection definition plus all exceptions relative to object allocation Description connect This method opens a connection to a specified database on a given PostgreSQL server You can use key words here as described in the Python tutorial The names of the key words are the name of the parameters given in the syntax line For a precise description of the parameters please refer to the PostgreSQL user manual Examples import pg conl pg connect testdb myhost 5432 None None bob None con2 pg connect dbname testdb host localhost user bob 115 connect 116 get defhost Name get defhost get default host name DV Synopsis get defhost Parameters none Return Type string or None Default host specification Exceptions SyntaxError Too many arguments Description get defhost returns the current default host specification or None if the environment variables should be used Environment variables will not be looked up 117 set defhost Name set defhost set default host name DV Synopsis set defhost host Parameters host New default host string None Return Type string or None Previous default ho
221. est INFO trigf fired after there are 1 tuples in ttest INFO trigf fired before there are 1 tuples in ttest INFO trigf fired after there are 0 tuples in ttest remember what we said about visibility DELETE 2 vac SELECT FROM ttest x 0 rows 259 Chapter 17 Server Programming Interface The Server Programming Interface SPI gives users the ability to run SQL queries inside user defined C functions Note The available Procedural Languages PL give an alternate means to build functions that can execute queries In fact SPI is just a set of native interface functions to simplify access to the Parser Planner Optimizer and Executor SPI also does some memory management To avoid misunderstanding we ll use function to mean SPI interface functions and procedure for user defined C functions using SPI Procedures which use SPI are called by the Executor The SPI calls recursively invoke the Executor in turn to run queries When the Executor is invoked recursively it may itself call procedures which may make SPI calls Note that if during execution of a query from a procedure the transaction is aborted then control will not be returned to your procedure Rather all work will be rolled back and the server will wait for the next command from the client This will probably be changed in future versions A related restriction is the inability to execute BEGIN END and ABORT transaction control statements This
222. esult solves one of PQexec s problems If a command string contains multiple SQL commands the results of those commands can be obtained individually This allows a simple form of overlapped processing by the way the frontend can be handling the results of one query while the backend is still working on later queries in the same command string However calling PQge tResult will still cause the frontend to block until the backend completes the next SQL command This can be avoided by proper use of three more functions POconsumeInput If input is available from the backend consume it int PQconsumeInput PGconn conn POconsumeInput normally returns 1 indicating no error but returns 0 if there was some kind of trouble in which case POerrorMessage is set Note that the result does not say whether any input data was actually collected After calling POconsumeInput the application may check PQisBusy and or POnot i fies to see if their state has changed POconsumeInput may be called even if the application is not prepared to deal with a result or notifi cation just yet The routine will read available data and save it in a buffer thereby causing a select read ready indication to go away The application can thus use POconsumeInput to clear the se lect condition immediately and then examine the results at leisure 14 Chapter 1 libpq C Library e PQisBusy Returns 1 if a query is busy that is POget Result would block wait
223. eturning composite build TupleDesc and perhaps AttInMetadata obtain slot funcctx gt slot slot endif returning composite user defined code MemoryContextSwitchTo oldcontext each time setup code appears here us r defined code funcctx SRF PERCALL SETUP us r defined code this is just one way we might test whether we are done if funcctx call cntr funcctx max calls else here we want to return another item user defined code obtain result Datum SRF_RETURN_NEXT funcctx result here we are done returning items and just need to clean up user defined code SRF RETURN DONE funcctx A complete example of a simple SRF returning a composite type looks like PG FUNCTION INFO V1 testpassbyval Datum testpassbyval PG FUNCTION ARGS FuncCallContext funcctx int call cntr int max calls TupleDesc tupdesc TupleTableSlot SloLb AttInMetadata attinmeta stuff done only on the first call of the function du SRF_IS_FIRSTCALL 196 Chapter 9 Extending SQL Functions MemoryContext oldcontext create a function context for cross call persistence funcctx SRF FIRSTCALL INIT switch to memory context appropriate for multiple function calls oldcontext MemoryContextSwitchTo funcctx multi call memory ctx tota
224. expects to find the shared library files 9 6 Function Overloading More than one function may be defined with the same SQL name so long as the arguments they take are different In other words function names can be overloaded When a query is executed the server will determine which function to call from the data types and the number of the provided arguments Overloading can also be used to simulate functions with a variable number of arguments up to a finite maximum number A function may also have the same name as an attribute In the case that there is an ambiguity between a function on a complex type and an attribute of the complex type the attribute will always be used When creating a family of overloaded functions one should be careful not to create ambiguities For instance given the functions CREATE FUNCTION test int real RETURNS CREATE FUNCTION test smallint double precision RETURNS it is not immediately clear which function would be called with some trivial input like test 1 1 5 The currently implemented resolution rules are described in the User s Guide but it is unwise to design a system that subtly relies on this behavior When overloading C language functions there is an additional constraint The C name of each function in the family of overloaded functions must be different from the C names of all other functions either internal or dynamically loaded If this rule is violated the beh
225. extending 215 alias See label for table name in query all and operator any anyarray arrays constants Australian time zones auto increment See serial autocommit average function B tree See indexes backup between bigint bigserial binary strings concatenation length bison bit strings constants data type BLOB See large object Boolean data type operators See operators logical box data type BSD OS case case sensitivity SQL commands catalogs 171 character set encoding character strings concatenation constants data types length cid cidr circle client authentication cluster column columns system columns col description comments in SQL comparison operators concurrency conditionals configuration server configure connection loss 55 constants COPY with libpq 17 count CREATE TABLE createdb crypt cstring currval 361 data area See database cluster data types 171 constants extending 206 numeric type casts database creating database cluster date constants current data type output format See Also Formatting date style deadlock timeout decimal See numeric DELETE Digital UNIX See Tru64 UNIX dirty read disk space disk us
226. fd lo open conn lob jId INV WRITE read in from the Unix file and write to the inversion file A while nbytes read fd buf BUFSIZE gt 0 tmp lo write conn 1obj fd buf nbytes if tmp nbytes fprintf stderr error while reading large object n void close fd void lo close conn 1lobj fd return lobjId void 36 Chapter 2 Large Objects pickout PGconn conn Oid lobjId int start int len int lobj_fd char buf int nbytes int nread lobj fd lo open conn lob jId INV READ if 10bj fd 0 fprintf stderr can t open large object d n lobjId lo lseek conn lobj_fd start SEEK SET buf malloc len 1 nread 0 while len nread gt 0 nbytes lo read conn lobj_fd buf len nread buf nbytes fprintf stderr gt gt gt s buf nread nbytes free buf fprintf stderr n lo_close conn lobj_fd void overwrite PGconn conn Oid lobjId int start int len int lobj fd char buf int nbytes int nwritten int alee lobj fd lo open conn lob jId INV READ if lobj td 0 fprintf stderr can t open large object d n lobjId lo lseek conn lobj_fd start SEEK SET buf malloc len 1 for i 0 i lt len i buf i X buf i 37 Chapter 2 Large Objects nwritten 0 while len nwritten gt 0
227. fields are customarily numbered in PostgreSQL STG_when The string BEFORE or AFTER depending on the type of trigger call STG_level The string ROW or STATEMENT depending on the type of trigger call STG_op The string INSERT UPDATE or DELE E depending on the type of trigger call SNEW An associative array containing the values of the new table row for INSERT UPDATE actions or empty for DELETE The array is indexed by field name Fields that are NULL will not appear in the array SOLD An associative array containing the values of the old table row for UPDATE DELETE actions or empty for INSERT The array is indexed by field name Fields that are NULL will not appear in the array Sargs A Tcl list of the arguments to the procedure as given in the CREATE TRIGGER statement These arguments are also accessible as 1 n in the procedure body The return value from a trigger procedure can be one of the strings OK or SKIP or a list as returned by the array get Tcl command If the return value is OK the operation INSERT UPDATE DELETE that fired the trigger will proceed normally SKIP tells the trigger manager to silently suppress the operation for this row If a list is returned it tells PL Tcl to return a modified row to the trigger manager that will be inserted instead of the one given in NEW this works for INSERT UPDATE only Needless to say that all this is only meani
228. for the full path to the PostgreSQL source tree Better style would be to use just funcs in the AS clause after having added PGROOT tutorial to the search path In any case we may omit the system specific extension for a shared library commonly so or s1 Notice that we have specified the functions as ot rict meaning that the system should automatically assume a NULL result if any input value is NULL By doing this we avoid having to check for NULL inputs in the function code Without this we d have to check for null values explicitly for example by 187 Chapter 9 Extending SQL Functions checking for a null pointer for each pass by reference argument For pass by value arguments we don t even have a way to check Although this calling convention is simple to use it is not very portable on some architectures there are problems with passing smaller than int data types this way Also there is no simple way to return a NULL result nor to cope with NULL arguments in any way other than making the function strict The version 1 convention presented next overcomes these objections 9 5 4 Version 1 Calling Conventions for C Language Functions The version 1 calling convention relies on macros to suppress most of the complexity of passing argu ments and results The C declaration of a version 1 function is always Datum funcname PG FUNCTION ARGS In addition the macro call PG FUNCTION INFO Vi1 funcname m
229. form however If you would like to send mail but do not want to receive list traffic you can subscribe and set your subscription option to nomail For more information send mail to lt majordomo postgresql org gt with the single word help in the body of the message ix I Client Interfaces This part of the manual is the description of the client side programming interfaces and support libraries for various languages Chapter 1 libpq C Library 1 1 Introduction libpq is the C application programmer s interface to PostgreSQL libpq is a set of library routines that allow client programs to pass queries to the PostgreSQL backend server and to receive the results of these queries libpq is also the underlying engine for several other PostgreSQL application interfaces including libpqt C 1ibpgtc1 Tcl Perl and ecpg So some aspects of libpq s behavior will be important to you if you use one of those packages Three short programs are included at the end of this section to show how to write programs that use libpq There are several complete examples of 1ibpq applications in the following directories src test examples src bin psql Frontend programs that use 1ibpq must include the header file 1ibpq fe h and must link with the libpq library 1 2 Database Connection Functions The following routines deal with making a connection to a PostgreSQL backend server The application program can have several backend connections
230. functionality in the near future PQisnonblocking Returns the blocking status of the database connection int PQisnonblocking const PGconn conn Returns if the connection is set to nonblocking mode 0 if blocking PQsendQuery Submit a command to the server without waiting for the result s 1 is returned if the command was successfully dispatched 0 if not in which case use POerrorMessage to get more information about the failure int PQsendQuery PGconn conn const char query After successfully calling POsendQuery call PQgetResult one or more times to obtain the results PQsendQuery may not be called again on the same connection until PQgetResult has returned NULL indicating that the command is done PQgetResult Wait for the next result from a prior PQsendQuery and return it NULL is returned when the query is complete and there will be no more results PGresult PQgetResult PGconn conn POgetResult must be called repeatedly until it returns NULL indicating that the command is done If called when no command is active POget Result will just return NULL at once Each non NULL result from PQgetResult should be processed using the same PGresult accessor functions previ ously described Don t forget to free each result object with PQclear when done with it Note that POgetResult will block only if a query is active and the necessary response data has not yet been read by POconsumeInput Using POsendQuery and PQgetR
231. g the Driver iere eto ea idee t te eben TI 5 1 2 Setting up the Class Pathos sineren nenn rennen nennen TI 5 1 3 Preparing the Database for JDBC sees 78 23 2 Using the Driver ssi hen AR RE 78 92 1 Importing JDBC eo eee a HERI 78 3 2 2 roading the DriVerc est eto eae dp t t etes 78 5 2 3 Connecting to the Database eeesssseeseeeeeeeennen etre 79 23 2 4 Closmg the Connection i eden eR UP eroi ee ies 79 5 3 Issuing a Query and Processing the Result eesseeeeeeeenen 80 5 3 1 Using the Statement or PreparedStatement Interface 80 5 3 2 Using the ResultSet Interface sese 81 544 Performing Updates negotii peii 81 5 5 Creating and Modifying Database Objects sse 82 5 6 Storing Binary Datars ert oe ep eee deri e eno ERO PER edP Rd 82 5 7 PostgreSQL Extensions to the JDBC API eee enne 85 5 7 1 Accessing the EXtensiOns 3 ne teret tette iere pe tteeeis 85 5 7 1 1 Class org postgresql PGCOnnectioOn sseeeeseereeesseeeesereeseeseeeeseeee 85 5 71 1 T Methods essen sepe eeegGohieaehep t 85 5 7 1 2 Class otg postgresql Fastpath veea e E enne enne 86 5 71 21 Methods innin era oU REOR e 87 5 7 1 3 Class org postgresql fastpath FastpathArg eee 89 5 7 1 3 Constr ctors ieu peg eere irre 89 5 7 2 Geometric Data Types iere rte it nte eine E 90 3 4 3
232. ge SPI saveplan saves a passed plan prepared by SPI_prepare in memory protected from freeing by SPI finish and by the transaction manager and returns a pointer to the saved plan You may save the 276 SPI saveplan pointer returned in a local variable Always check if this pointer is NULL or not either when preparing a plan or using an already prepared plan in SPI execp see below Note If one of the objects a relation function etc referenced by the prepared plan is dropped during your session by your backend or another process then the results of sP1 execp for this plan will be unpredictable 277 17 2 Interface Support Functions The functions described here provide convenient interfaces for extracting information from tuple sets returned by SPI exec and other SPI interface functions All functions described in this section may be used by both connected and unconnected procedures SPI fnumber Name SPI fnumber Finds the attribute number for specified attribute name Synopsis SPI fnumber tupdesc fname Inputs TupleDesc tupdesc Input tuple description char fname Field name Outputs int Attribute number Valid one based index number of attribute SPI ERROR NOATTRIBUTE if the named attribute is not found Description SPI fnumber returns the attribute number for the attribute with name in fname 278 SPI fnumber Usage Attribute numbers are 1 based If the given fname refers to a system
233. ge Handlers essent eerte enne 203 10 Extending SQL Dypes uui i t eee eee cet Ie Rt E 206 11 Extending SQL Operators netter e eee brit PARE rhe eite ibo dpbit ens 209 11 1 Introduction 1 Reto d epe tere gie eg Saabs 209 11 2 Example niet Dt He BED du ee 209 11 3 Operator Optimization Information essere 210 11 3 3 COMMUTATOR riot Pet epe REOR derer 210 11 3 2 NEGATOR Rega DRE IE gdsenee bre 210 11 3 3 RESTRICTS iore bue E gt adiit e besiegt 211 11 34 JOIN eie in e cete tet ete t io ie eie ttes ae 212 11 3 5 HASHES eue nece is ERI TEE RU e EE REIR ER 212 11 3 6 MERGES SORT1 SORT2 LTCMP GICMP ccsssccccesssscccescsssececcesssnseceeesensceeeeees 213 12 Extending SQL Aggregates iare A eerie EEE ennt entrent nennen 215 13 The Rule SyStent a oe ee eee oO ee ee eme ipetiteste A Sede dus dda Sayed neecegetbdy ee ced 217 133 Introduction iiie pen egere ferre a 217 13 2 Whatis a Query Tree osse e p it ca t PE AER PERRO ORNA 217 13 2 1 The Parts of a Query tree isset ether etre teer Tecta 217 13 3 Views andthe Rule System ede re e o e e hes eg 219 13 3 1 Implementation of Views in PostgreSQL eee 219 13 3 2 How SELECT Rules Wotk ite tee ede e to eed 219 13 3 3 View Rules in Non SELECT Statements eee 225 13 3 4 The Power of Views in PostgreSQL esee 226 13 341 Benehts eR RI RS 226 v
234. ge object call Oid lo_import PGconn conn const char filename filename specifies the operating system name of the file to be imported as a large object 2 3 3 Exporting a Large Object To export a large object into an operating system file call int lo export PGconn conn Oid lobjId const char filename The lobjId argument specifies the OID of the large object to export and the filename argument specifies the operating system name name of the file 33 Chapter 2 Large Objects 2 3 4 Opening an Existing Large Object To open an existing large object call int lo open PGconn conn Oid lobjId int mode The lobjId argument specifies the OID of the large object to open The mode bits control whether the object is opened for reading INV READ writing INV WRITE or both A large object cannot be opened before it is created 1o open returns a large object descriptor for later use in 1o read 1o write lo lseek lo_tell and 1o close 2 3 5 Writing Data to a Large Object The routine int lo write PGconn conn int fd const char buf size t len writes len bytes from buf to large object fd The fd argument must have been returned by a previous lo open The number of bytes actually written is returned In the event of an error the return value is negative 2 3 6 Reading Data from a Large Object The routine int lo read PGconn conn int fd char buf size t len reads len bytes from large object d into buf
235. ge objects However sometimes lower level access to Large Objects is required that is not supported by the JDBC specification Refer to org postgresql largeobject LargeObject on how to manipulate the contents of a Large Object 5 7 3 2 1 Variables public static final int WRITE This mode indicates we want to write to an object public static final int READ This mode indicates we want to read an object public static final int READWRITE This mode is the default It indicates we want read and write access to a large object 5 7 3 2 2 Methods public LargeObject open int oid throws SQLException This opens an existing large object based on its OID This method assumes that READ and WRITE access is required the default public LargeObject open int oid int mode throws SQLException This opens an existing large object based on its OID and allows setting the access mode public int create throws SQLException This creates a large object returning its OID It defaults to READWRITE for the new object s attributes public int create int mode throws SQLException This creates a large object returning its OID and sets the access mode public void delete int oid throws SQLException This deletes a large object public void unlink int oid throws SQLException 106 Chapter 5 JDBC Interface This deletes a large object It is identical to the delete meth
236. ghtly different In that case the individual items to return are specified in RETURN NEXT commands and then a final RETURN command with no arguments is used to indicate that the function has finished executing RETURN NEXT can be used with both scalar and composite data types in the later case an entire table of results will be returned Functions that use RETURN NEXT should be called in the following fashion SELECT FROM some func That is the function is used as a table source in a FROM clause RETURN NEXT expression RETURN NEXT does not actually return from the function it simply saves away the value of the expres sion or record or row variable as appropriate for the data type being returned Execution then continues with the next statement in the PL pgSQL function As successive RETURN NEXT commands are exe cuted the result set is built up A final RETURN which need have no argument causes control to exit the function Note The current implementation of RETURN NEXT for PL pgSQL stores the entire result set before returning from the function as discussed above That means that if a PL pgSQL function produces 320 Chapter 19 PL pgSQL SQL Procedural Language a very large result set performance may be poor data will be written to disk to avoid memory ex haustion but the function itself will not return until the entire result set has been generated A future version of PL pgSQL may allow
237. gt FOR record row IN select query LOOP statements END LOOP The record or row variable is successively assigned all the rows resulting from the SELECT query and the loop body is executed for each row Here is an example CREATE FUNCTION cs refresh mviews RETURNS INTEGER AS DECLARE mviews RECORD BEGIN a ERFORM cs log Refreshing materialized views FOR mviews IN SELECT FROM cs materialized views ORDER BY sort key LOOP Now mviews has one record from cs materialized views PERFORM cs log Refreshing materialized view quote ident mviews mv name EXECUTE TRUNCATE ABLE quote ident mviews mv name EXECUTE INSERT INTO quote ident mviews mv name mviews mv quer END LOOP PERFORM cs log Done refreshing materialized views RETURN 1 end LANGUAGE plpgsql If the loop is terminated by an EXIT statement the last assigned row value is still accessible after the loop The FOR IN EXECUTE statement is another way to iterate over records 325 Chapter 19 PL pgSQL SQL Procedural Language lt lt label gt gt FOR record row IN EXECUTE text expression LOOP statements END LOOP This is like the previous form except that the source SELECT statement is specified as a string expression which is evaluated and re planned on
238. hat the C language function name is the same as the SQL name Normally all internal functions present in the backend are declared during the initialization of the database cluster initdb but a user could use CREATE FUNCTION to create additional alias names for an inter nal function Internal functions are declared in CREATE FUNCTION with language name internal For Hy instance to create an alias for the sqrt function CREATE FUNCTION square_root double precision RETURNS double precision AS dsqrt LANGUAGE INTERNAL WITH isStrict Most internal functions expect to be declared strict Note Not all predefined functions are internal in the above sense Some predefined functions are written in SQL 181 Chapter 9 Extending SQL Functions 9 5 C Language Functions User defined functions can be written in C or a language that can be made compatible with C such as C Such functions are compiled into dynamically loadable objects also called shared libraries and are loaded by the server on demand The dynamic loading feature is what distinguishes C language functions from internal functions the actual coding conventions are essentially the same for both Hence the standard internal function library is a rich source of coding examples for user defined C functions Two different calling conventions are currently used for C functions The newer
239. he last query was executed is returned in the global variable SPI processed if not SPI OK UTILITY If SPI OK SELECT is returned then you may use global pointer SPITupleTable SPI tuptable to access the result tuples SPI exec may return one of the following negative values SPI ERROR ARGUMENT if query is NULL or tcount lt 0 SPI ERROR UNCONNECTED if procedure is unconnected SPI ERROR COPY if COPY TO FROM stdin SPI ERROR CURSOR if DECLARE CLOSE CURSOR FETCH SPI ERROR TRANSACTION if BEGIN ABORT END SPI ERROR OPUNKNOWN if type of query is unknown this shouldn t occur Structures If SPI OK SELECT is returned then you may use the global pointer SPITupleTable SPI tuptable to access the selected tuples Structure SPITupleTable is defined in spi h typedef struct MemoryContext tuptabcxt memory context of result table uint32 alloced of alloced vals uint32 free 4 of free vals TupleDesc tupdesc tuple descriptor HeapTuple vals tuples 264 SPI exec SPITupleTable vals is an array of pointers to tuples the number of useful entries is given by SPI processed tupdesc is a tuple descriptor which you may pass to SPI functions dealing with tuples tuptabcxt alloced and free are internal fields not intended for use by SPI callers Note Functions sPr exec SPI execp and sPrI prepare change both SPI processed and SPI tuptable just the pointer not the contents of the stru
240. he 1ibecpg library like so cc o myprog progl o prog2 o lecpg Again you might have to add an option like L usr local pgsql lib to that command line If you manage the build process of a larger project using make it may be convenient to include the following implicit rule to your makefiles ECPG ecpg c pgc S ECPG lt The complete syntax of the ecpg command is detailed in the PostgreSQL Reference Manual 73 Chapter 4 ECPG Embedded SQL in C 4 9 Library Functions The 1ibecpg library primarily contains hidden functions that are used to implement the functionality expressed by the embedded SQL commands But there are some functions that can usefully be called directly Note that this makes your code unportable ECPGdebug int on FILE stream turns on debug logging if called with the first argument non zero Debug logging is done on st ream Most SQL statement log their arguments and results The most important function ECPGdo logs all SQL statements with both the expanded string i e the string with all the input variables inserted and the result from the PostgreSQL server This can be very useful when searching for errors in your SQL statements ECPGstatus This method returns true if we are connected to a database and false if not 4 10 Porting From Other RDBMS Packages The design of ecpg follows the SQL standard Porting from a standard RDBMS should not be a problem U
241. he PostgreSQL large object Exceptions TypeError Bad argument type or too many arguments pg error Invalid connection or creation error Description locreate method creates a large object in the database The mode can be defined by OR ing the constants defined in the pg module INv READ and INV WRITE 137 getlo Name getlo build a large object from given OID LO Synopsis getlo oid Parameters oid OID of the existing large object integer Return Type pglarge Object handling the PostgreSQL large object Exceptions TypeError Bad argument type or too many arguments pg error Invalid connection Description getlo method allows to reuse a formerly created large object through the pglarge interface providing the user has its OID 138 loimport Name loimport import a file to a PostgreSQL large object LO Synopsis loimport filename Parameters filename The name of the file to be imported string Return Type pglarge Object handling the PostgreSQL large object Exceptions TypeError Bad argument type or too many arguments pg error Invalid connection or error during file import Description loimport method allows to create large objects in a very simple way You just give the name of a file containing the data to be use 139 6 4 Database Wrapper Class DB pg module contains a class called DB All pgob ject methods ar
242. he frontend backend communication to a debugging file stream void PQtrace PGconn conn FILE debug port 19 Chapter 1 libpq C Library PQuntrace Disable tracing started by POt race void PQuntrace PGconn conn 1 9 libbq Control Functions POsetNoticeProcessor Control reporting of notice and warning messages generated by libpq typedef void POnoticeProcessor void arg const char message POnoticeProcessor PQsetNoticeProcessor PGconn conn PQnoticeProcessor proc void arg By default libpq prints notice messages from the backend on stderr as well as a few error messages that it generates by itself This behavior can be overridden by supplying a callback function that does something else with the messages The callback function is passed the text of the error message which includes a trailing newline plus a void pointer that is the same one passed to POset Not iceProcessor This pointer can be used to access application specific state if needed The default notice processor is simply static void defaultNoticeProcessor void arg const char message fprintf stderr Ss message To use a special notice processor call PQsetNoticeProcessor just after creation of a new PGconn object The return value is the pointer to the previous notice processor If you supply a callback function pointer of NULL no action is taken but the current pointer is returned Once you have set a notice processo
243. he program to the database for example as parameters in a query or to pass data from the database back to the program the C variables that are intended to contain this data need to be declared in a specially marked section so the embedded SQL preprocessor is made aware of them This section starts with EX EC SQL B EGIN D ECLARE n ECTION and ends with 68 Chapter 4 ECPG Embedded SQL in C EXEC SQL END DECLARE n ECTION Between those lines there must be normal C variable declarations such as int X char foo 16 bar 16 The declarations are also echoed to the output file as a normal C variables so there s no need to declare them again Variables that are not intended to be used with SQL commands can be declared normally outside these special sections The definition of a structure or union also must be listed inside a DECLARE section Otherwise the prepro cessor cannot handle these types since it does not know the definition The special types VARCHAR and VARCHAR2 are converted into a named struct for every variable A declaration like VARCHAR var 180 is converted into struct varchar_var int len char arr 180 var This structure is suitable for interfacing with SQL datums of type VARCHAR To use a properly declared C variable in an SQL statement write varname where an expression is expected See the previous section fo
244. he view The resulting rewritten parse tree is almost the same as if Al had typed SELECT shoelace sl name shoelace sl avail shoelace sl color shoelace sl len shoelace sl unit shoelace sl len cm FROM SELECT s sl name Sl avail 5h Color sl_len Sl unit HAN DDN 0 Sl len u un fact AS sl len cm FROM shoelace data s unit u WHERE s sl unit u un name shoelace There is one difference however the sub query s range table has two extra entries shoelace OLD shoelace NEW These entries don t participate directly in the query since they aren t referenced by the sub query s join tree or target list The rewriter uses them to store the access permission check info that was originally present in the range table entry that referenced the view In this way the executor will still check that the user has proper permissions to access the view even though there s no direct use of the view in the rewritten query That was the first rule applied The rule system will continue checking the remaining range table entries in the top query in this example there are no more and it will recursively check the range table entries in the added sub query to see if any of them reference views But it won t expand OLD or NEW otherwise we d have infinite recursion In this example there are no rewrite rules for shoelace data or unit so rewriting is complete and the above is the final result given
245. hould make some of these join queries which are often three or four way joins more understandable because you will be able to see that the columns used in the queries form foreign keys in other tables Many different features tables columns functions types access methods etc are tightly integrated in this schema A simple create command may modify many of these catalogs Types and procedures are central to the schema Note We use the words procedure and function more or less interchangeably Nearly every catalog contains some reference to rows in one or both of these tables For example PostgreSQL frequently uses type signatures e g of functions and operators to identify unique rows of other catalogs There are many columns and relationships that have obvious meanings but there are many particularly those that have to do with access methods that do not 174 Chapter 9 Extending SQL Functions 9 1 Introduction PostgreSQL provides four kinds of functions query language functions functions written in SQL procedural language functions functions written in for example PL Tcl or PL pgSQL internal functions Clanguage functions Every kind of function can take a base type a composite type or some combination as arguments param eters In addition every kind of function can return a base type or a composite type It s easiest to define SQL functions so we ll start with those Examples in this s
246. id 3 IF users rec homepage IS NULL THEN user entered no homepage return http RETURN http END IF END 19 5 3 Executing an expression or query with no result Sometimes one wishes to evaluate an expression or query but discard the result typically because one is calling a function that has useful side effects but no useful result value To do this in PL pgSQL use the PERFORM statement PERFORM query This executes a SELECT query and discards the result PL pgSQL variables are substituted in the query as usual Also the special variable FOUND is set to true if the query produced at least one row or false if it produced no rows Note One might expect that SELECT with no INTO clause would accomplish this result but at present the only accepted way to do it is PERFORM An example PERFORM create mv cs session page requests mv my query 317 Chapter 19 PL pgSQL SQL Procedural Language 19 5 4 Executing dynamic queries Oftentimes you will want to generate dynamic queries inside your PL pgSQL functions that is queries that will involve different tables or different data types each time they are executed PL pgSQL s normal attempts to cache plans for queries will not work in such scenarios To handle this sort of problem the EXECUTE statement is provided EXECUTE query string where query string is an expression yielding a string of type text cont
247. ied by the input variables i e the variables that where not known at compile time but are to be entered in the query Where the variables should go the string contains Input variables As described in the section about the preprocessor every input variable gets ten arguments ECPGt EOIT An enum telling that there are no more input variables Output variables As described in the section about the preprocessor every input variable gets ten arguments These variables are filled by the function ECPGt EORT An enum telling that there are no more variables 76 Chapter 5 JDBC Interface Author Originally written by Peter T Mount lt peter retep org uk gt the original author of the JDBC driver JDBC is a core API of Java 1 1 and later It provides a standard set of interfaces to SQL compliant databases PostgreSQL provides a type 4 JDBC Driver Type 4 indicates that the driver is written in Pure Java and communicates in the database system s own network protocol Because of this the driver is platform independent once compiled the driver can be used on any system This chapter is not intended as a complete guide to JDBC programming but should help to get you started For more information refer to the standard JDBC API documentation Also take a look at the examples included with the source The basic example is used here 5 1 Setting up the JDBC Driver 5 1 1 Getting the Driver Precompiled versions of the driver
248. if a new line consists of the two characters V which in dicates that the backend server has finished sending the results of the copy command If the application might receive lines that are more than length 1 characters long care is needed to be sure one recognizes the line correctly and does not for example mistake the end of a long data line for a terminator line The code in src bin psql copy c contains example routines that correctly handle the copy protocol PQgetlineAsync Reads a newline terminated line of characters transmitted by the backend server into a buffer without blocking int POgetlineAsync PGconn conn char buffer int bufsize This routine is similar to POgetline but it can be used by applications that must read COPY data asynchronously that is without blocking Having issued the COPY command and gotten a PGRES COPY OUT response the application should call PQconsumeInput and PQgetlineAsync until the end of data signal is detected Unlike PQgetline this routine takes responsibility for detecting end of data On each call POgetlineAsync will return data if a complete newline terminated data line is available in libpq s input buffer or if the incoming data line is too long to fit in the buffer offered by the caller Otherwise no data is returned until the rest of the line arrives The routine returns 1 if the end of copy data marker has been recognized or 0 if no data is available or a positive number g
249. ii 13 3 5 What about updating a view sssssesssseeeeeeeeeeeeennen enne 226 13 4 Rules on INSERT UPDATE and DELETE eene 221 13 4 1 Differences from View Rules eese 227 13 4 2 How These Rules WOEK 5 epe merecen iet ee erem enema ede 227 13 4 2 1 A First Rule Step by Step 228 13 4 3 Cooperation with VIEWS ies coiere eren ree e eR Reds 231 13 5 Rules and Permissions sseseeesesseseeeeeeeee eren nennen nennen enne eene 237 13 6 Rules and Command Status eese nenne nennen eren nennen 238 13 7 Rules versus Trgg ets c rg regem RE ERE EE Rer eee 239 14 Interfacing Extensions To Indexes esses ener enne enne ene nen nennen nene 242 T4 1 InttOdU CctiOR i5 oir rette Podere eee rS ERE EE e teen een 242 14 2 Access Methods and Operator Classes sess 242 14 3 Access Method Strategies enne isterse oere s 242 14 4 Access Method Support Routines eeesseseseeeeeeeee eene eene enne 244 14 5 Creating the Operators and Support Routines seeeeeeeenree 245 14 6 Creating the Operator Class etre the ert pietre 246 14 7 Special Features of Operator Classes esses 247 15 Index Cost Estimation Functions eeesssseseeseeeeeeee eene en en nennen eterne enne 249 LG Trig BETS PC Et 252 16 1 Trigger Definition neo rd deter needed
250. ild2 Child3 rows w ECT name listchildren name T listchildren name RETURNS SETOF 1 parent FROM nodes text AS 180 Chapter 9 Extending SQL Functions op Childl op Child2 Top Ghild3 Childl SubChildl Childl SubChild2 5 rows In the last SELECT notice that no output row appears for Child2 Child3 etc This happens because listchildren returns an empty set for those inputs so no output rows are generated 9 3 Procedural Language Functions Procedural languages aren t built into the PostgreSQL server they are offered by loadable modules Please refer to the documentation of the procedural language in question for details about the syntax and how the function body is interpreted for each language There are currently four procedural languages available in the standard PostgreSQL distribution PL pgSQL PL Tcl PL Perl and PL Python Other languages can be defined by users Refer to Chapter 18 for more information The basics of developing a new procedural language are covered in Section 9 8 9 4 Internal Functions Internal functions are functions written in C that have been statically linked into the PostgreSQL server The body of the function definition specifies the C language name of the function which need not be the same as the name being declared for SQL use For reasons of backwards compatibility an empty body is accepted as meaning t
251. inate coordinate public PGlseg PGpoint pl PGpoint p2 Parameters pl first point for first point for first point for second point for second point p2 second point public PGlseg String s throws SQLException Parameters S Definition of the line segment in PostgreSQL s syntax Throws SQLEx ception on conversion failure public PGlseg required by the driver Methods public void setValue String s throws SQLException Parameters S Definition of the line segment in PostgreSQL s syntax Throws SQLException on conversion failure Overrides setValue in class PGobject public boolean equals Object obj Parameters obj Object to compare with 96 Chapter 5 JDBC Interface Returns true if the two line segments are identical Overrides equals in class PGobject public Object clone This must be overridden to allow the object to be cloned Overrides clone in class PGobject public String getValue Returns the PGlseg in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGpath java lang Object l t org postgresql util PGobject t org postgresql geometric PGpath public class PGpath extends PGobject implements Serializable Cloneable This implements a path a multiply segmented line which may be closed Variables public boolean open True if the path is open false if closed
252. ine the effect of a command The first method is to use the GET DIAG NOSTICS which has the form GET DIAGNOSTICS variable item This command allows retrieval of system status indicators Each item is a keyword identifying a state value to be assigned to the specified variable which should be of the right data type to receive it The currently available status items are ROW COUNT the number of rows processed by the last SQL query sent down to the SQL engine and RESULT OrID the OID of the last row inserted by the most recent SQL query Note that RESULT OID is only useful after an INSERT query Q ET DIAGNOSTICS var integer ROW COUNT There is a special variable named FOUND of type boolean FOUND starts out false within each PL pgSQL function It is set by each of the following types of statements A SELECT INTO statement sets FOUND true if it returns a row false if no row is returned A PERFORM statement sets FOUND true if it produces discards a row false if no row is produced UPDATE INSERT and DELETE statements set FOUND true if at least one row is affected false if no row is affected 319 Chapter 19 PL pgSQL SQL Procedural Language A FETCH statement sets FOUND true if it returns a row false if no row is returned A FOR statement sets FOUND true if it iterates one or more times else false This applies to all three variants of the FOR statement integer FOR loops recor
253. ines must deal with data type conversion when STORAGE is used 248 Chapter 15 Index Cost Estimation Functions Author Written by Tom Lane lt tgl sss pgh pa us gt on 2000 01 24 Note This must eventually become part of a much larger chapter about writing new index access methods Every index access method must provide a cost estimation function for use by the planner optimizer The procedure OID of this function is given in the amcostestimate field of the access method s pg am entry Note Prior to PostgreSQL 7 0 a different scheme was used for registering index specific cost esti mation functions The amcostestimate function is given a list of WHERE clauses that have been determined to be usable with the index It must return estimates of the cost of accessing the index and the selectivity of the WHERE clauses that is the fraction of main table tuples that will be retrieved during the index scan For simple cases nearly all the work of the cost estimator can be done by calling standard routines in the optimizer the point of having an amcostestimate function is to allow index access methods to provide index type specific knowledge in case it is possible to improve on the standard estimates Each amcostestimate function must have the signature void amcostestimate Query root RelOptInfo rel IndexOptInfo index List indexQuals Cost indexStartupCost Cost indexTotalCost Selectivity indexSelectivity doub
254. ing for input A 0 return indicates that POget Result can be called with assurance of not blocking int PQisBusy PGconn conn PQisBusy will not itself attempt to read data from the backend therefore PQconsumeInput must be invoked first or the busy state will never end PQflush Attempt to flush any data queued to the backend returns 0 if successful or if the send queue is empty or EOF if it failed for some reason int POflush PGconn conn PQflush needs to be called on a nonblocking connection before calling select to determine if a response has arrived If 0 is returned it ensures that there is no data queued to the backend that has not actually been sent Only applications that have used PQsetnonblocking have a need for this PQsocket Obtain the file descriptor number for the backend connection socket A valid descriptor will be gt 0 a result of 1 indicates that no backend connection is currently open int PQsocket const PGconn conn POsocket should be used to obtain the backend socket descriptor in preparation for executing se lect This allows an application using a blocking connection to wait for either backend responses or other conditions If the result of select indicates that data can be read from the backend socket then POconsumeInput should be called to read the data after which PQisBusy POgetResult and or POnotifies can be used to process the response Nonblocking connections that have used
255. insert a tuple into a database table Synopsis insert table a Parameters table Name of table A dictionary of values Return Type integer The OID of the newly inserted row Description This method inserts values into the table specified filling in the values from the dictionary It then reloads the dictionary with the values from the database This causes the dictionary to be updated with values that are modified by rules triggers etc Due to the way that this function works you will find inserts taking longer and longer as your table gets bigger To overcome this problem simply add an index onto the OID of any table that you think may get large over time 146 update Name update update a database table Synopsis update table a Parameters table Name of table A dictionary of values Return Type integer The OID of the newly updated row Description Similar to insert but updates an existing row The update is based on the OID value as munged by get The array returned is the one sent modified to reflect any changes caused by the update due to triggers rules defaults etc 147 clear Name clear clear a database table Synopsis clear table a Parameters table Name of table a A dictionary of values Return Type dictionary A dictionary with an empty row Description This method clears all the attributes to values determined by the t
256. int y pointy gt y PG RETURN POINT P new point By Reference Variable Length PG FUNCTION INFO V1 copytext Datum copytext PG FUNCTION ARGS text t PG GETARG TEXT P 0 VARSIZE is the total size of the struct in bytes id text new t text palloc VARSIZE t VARATT SIZEP new t VARSIZE t VARDATA is a pointer to the data region of the struct ES memcpy void VARDATA new_t destination void VARDATA t source VARSIZE t VARHDRSZ how many bytes PG RETURN TEXT P new t PG FUNCTION INFO V1 concat text Datum concat text PG FUNCTIO text argl PG GE text arg2 PG GE ARGS TARG TEXT P 0 TARG TEXT P 1 int32 new text siz text new text t Xt 7 VARSIZE argl VARSIZE arg2 VARHDRSZ palloc new text size 189 Chapter 9 Extending SQL Functions VARATT SIZEP new text new text size memcpy VARDATA new text VARDATA argl VARSIZE argl VARHDRSZ memcpy VARDATA new text VARSIZE argl VARHDRSZ VARDATA arg2 VARSIZE arg2 VARHDRSZ PG RETURN TEXT P new text The CREATE FUNCTION commands are the same as for the version 0 equivalents At first glance the version 1 coding conventions may appear to be just pointless obscurantism How ever they do offer a num
257. ion Use the accessor functions below to get at the contents of PGresult Avoid directly referencing the fields of the PGresult structure because they are subject to change in the future Beginning in PostgreSQL 6 4 the definition of struct PGresult is not even provided in 1ibpq fe h If you have old code that accesses PGresult fields directly you can keep using it by including 1ibpq int h too but you are encouraged to fix the code soon PQresultStatus Returns the result status of the command ExecStatusType POresultStatus const PGresult res PQresultStatus can return one of the following values PGRES EMPTY QUERY The string sent to the backend was empty PGRES COMMAND OK Successful completion of a command returning no data PGRES TUPLES OK The query successfully executed PGRES COPY OUT Copy Out from server data transfer started PGRES COPY IN Copy In to server data transfer started PGRES BAD RESPONSE The server s response was not understood PGRES NONFATAL ERROR PGRES FATAL ERROR If the result status is PGRES_TUPL ES OK then the routines described below can be used to retrieve the rows returned by the query Note that a SELECT command that happens to retrieve zero rows still shows PGRES TUPLES OK PGRES COMMAND OK is for commands that can never return rows INSERT UP DATE et
258. ion in the large object The whence parameter can be obtained by OR ing the constants defined in the pg module SEEK SET SEEK CUR SEEK END 161 tell Name tell return current position in the large object Synopsis tell Parameters none Return Type integer Current position in the object Exceptions SyntaxError Too many arguments IOError Object is not opened or seek error pg error Invalid connection or invalid object Description tell method allows to get the current position in the large object 162 unlink Name unlink delete the large object Synopsis unlink Parameters none Return Type none Exceptions SyntaxError Too many arguments IOError Object is not closed or unlink error pg error Invalid connection or invalid object Description unlink method unlinks deletes the large object 163 size Name size return the large object size Synopsis size Parameters none Return Type integer The large object size Exceptions SyntaxError Too many arguments IOError Object is not opened or seek tell error pg error Invalid connection or invalid object Description size method allows to get the size of the large object It was implemented because this function is very useful for a WWW interfaced database Currently the large object needs to be o
259. ions as well as user level performance tuning Every PostgreSQL user should read this PostgreSQL Administrator s Guide Installation and server management information Everyone who runs a PostgreSQL server either for personal use or for other users needs to read this PostgreSQL Programmer s Guide Advanced information for application programmers Topics include type and function extensibility library interfaces and application design issues PostgreSQL Reference Manual Reference pages for SQL command syntax and client and server programs This book is auxiliary to the User s Administrator s and Programmer s Guides PostgreSQL Developer s Guide Information for PostgreSQL developers This is intended for those who are contributing to the Post greSQL project application development information appears in the Programmer s Guide Preface In addition to this manual set there are other resources to help you with PostgreSQL installation and use man pages The Reference Manual s pages in the traditional Unix man format There is no difference in content FAQs Frequently Asked Questions FAQ lists document both general issues and some platform specific issues READMEs README files are available for some contributed packages Web Site The PostgreSQL web site carries details on the latest release upcoming features and other informa tion to make your work or play with PostgreSQL more productive Mailing Lists Th
260. ions in PostgreSQL are expressed as state values and state transition functions That is an aggregate can be defined in terms of state that is modified whenever an input item is processed To define a new aggregate function one selects a data type for the state value an initial value for the state and a state transition function The state transition function is just an ordinary function that could also be used outside the context of the aggregate A final function can also be specified in case the desired output of the aggregate is different from the data that needs to be kept in the running state value Thus in addition to the input and result data types seen by a user of the aggregate there is an internal state value data type that may be different from both the input and result types If we define an aggregate that does not use a final function we have an aggregate that computes a running function of the column values from each row Sum is an example of this kind of aggregate Sum starts at zero and always adds the current row s value to its running total For example if we want to make a sum aggregate to work on a data type for complex numbers we only need the addition function for that data type The aggregate definition is CREATE AGGREGATE complex sum sfunc complex add basetype complex stype complex initcond 0 0 SELECT complex_sum a FROM test_complex complex_sum In practic
261. ired operators and support routine we can finally create the operator class CREATE OPERATOR CLASS complex abs ops DEFAULT FOR TYPE complex USING btree AS OPERATOR 1 lt OPERATOR 2 em eg OPERATOR 3 Seg OPERATOR 4 m OPERATOR 5 3 FUNCTION 1 complex abs cmp complex complex And we re done Whew It should now be possible to create and use B tree indexes on complex columns We could have written the operator entries more verbosely as in OPERATOR 1 lt complex complex but there is no need to do so when the operators take the same data type we are defining the operator class for The above example assumes that you want to make this new operator class the default B tree operator class for the complex data type If you don t just leave out the word DEFAULT 14 7 Special Features of Operator Classes There are two special features of operator classes that we have not discussed yet mainly because they are not very useful with the default B tree index access method Normally declaring an operator as a member of an operator class means that the index access method can retrieve exactly the set of rows that satisfy a WHERE condition using the operator For example SELECT FROM table WHERE integer_column lt 4 can be satisfied exactly by a B tree index on the integer column But there are cases where an index is useful as an inexact guide to the matching row
262. ise a Python exception which if uncaught causes the PL Python module to call elog ERROR msg when the function handler returns from the Python interpreter Long jumping out of the Python interpreter is probably not good raise plpy ERROR msg and raise plpy FATAL msg are equivalent to calling plpy error and plpy fatal respectively Additionally the plpy module provides two functions called execute and prepare Calling plpy execute With a query string and an optional limit argument causes that query to be run and the result to be returned in a result object The result object emulates a list or dictionary object The result object can be accessed by row number and field name It has these additional methods nrows which returns the number of rows returned by the query and status which is the SPI exec return variable The result object can be modified For example rv plpy execute SELECT FROM my table 5 returns up to 5 rows from my table If my table has a column my ield it would be accessed as foo rv i my field The second function plpy prepare is called with a query string and a list of argument types if you have bind variables in the query For example plan plpy prepare SELECT last name FROM my users WHERE first name 1 text text is the type of the variable you will be passing as 1 After preparing a statement you use the function plpy execute t
263. it When you are defining a pair of commutative operators things are a little trickier how can the first one to be defined refer to the other one which you haven t defined yet There are two solutions to this problem One way is to omit the COMMUTATOR clause in the first operator that you define and then provide one in the second operator s definition Since PostgreSQL knows that commutative operators come in pairs when it sees the second definition it will automatically go back and fill in the missing COMMUTATOR clause in the first definition The other more straightforward way is just to include COMMUTATOR clauses in both definitions When PostgreSQL processes the first definition and realizes that COMMUTATOR refers to a non existent opera tor the system will make a dummy entry for that operator in the system catalog This dummy entry will have valid data only for the operator name left and right operand types and result type since that s all that PostgreSQL can deduce at this point The first operator s catalog entry will link to this dummy entry Later when you define the second operator the system updates the dummy entry with the ad ditional information from the second definition If you try to use the dummy operator before it s been filled in you ll just get an error message Note This procedure did not work reliably in PostgreSQL versions before 6 5 but it is now the recommended way to do things 210 Chapter 11
264. it carries additional information that helps the query planner optimize queries that use the operator Much of this chapter will be devoted to explaining that additional information 11 2 Example Here is an example of creating an operator for adding two complex numbers We assume we ve already created the definition of type complex see Chapter 10 First we need a function that does the work then we can define the operator CREATE FUNCTION complex add complex complex RETURNS complex AS PGROOT tutorial complex LANGUAGE C CREATE OPERATOR leftarg complex rightarg complex procedure complex_add commutator Now we can do SELECT a b AS c FROM test_complex 5 2 6 05 133 42 144 95 We ve shown how to create a binary operator here To create unary operators just omit one of leftarg for left unary or rightarg for right unary The procedure clause and the argument clauses are the only required items in CREATE OPERATOR The commutator clause shown in the example is an optional hint to the query optimizer Further details about commutator and other optimizer hints appear below 209 Chapter 11 Extending SQL Operators 11 3 Operator Optimization Information Author Written by Tom Lane A PostgreSQL operator definition can include several optional clauses that tell the system useful things about how the operator behaves These claus
265. ite system again and maybe more rules get applied resulting in more or less parse trees So the parse trees in the rule actions must have either another command type or another result relation Otherwise this recursive process will end up in a loop There is a compiled in recursion limit of currently 100 iterations If after 100 iterations there are still update rules to apply the rule system assumes a loop over multiple rule definitions and reports an error The parse trees found in the actions of the pg rewrite system catalog are only templates Since they can reference the range table entries for NEW and OLD some substitutions have to be made before they can be used For any reference to NEW the target list of the original query is searched for a corresponding entry If found that entry s expression replaces the reference Otherwise NEW means the same as OLD for an UPDATE or is replaced by NULL for an INSERT Any reference to OLD is replaced by a reference to the range table entry which is the result relation After we are done applying update rules we apply view rules to the produced parse tree s Views cannot insert new update actions so there is no need to apply update rules to the output of view rewriting 13 4 21 A First Rule Step by Step We want to trace changes to the sl avail column in the shoelace data relation So we setup a log table and a rule that conditionally writes a log entry when an UPDATE is performed on shoelace data
266. itive even though the rest of the EXEC SQL INCLUDE com mand follows the normal SQL case sensitivity rules 4 8 Processing Embedded SQL Programs Now that you have an idea how to form embedded SQL C programs you probably want to know how to compile them Before compiling you run the file through the embedded SQL C preprocessor which converts the SQL statements you used to special function calls After compiling you must link with a special library that contains the needed functions These functions fetch information from the arguments perform the SQL query using the libpq interface and put the result in the arguments specified for output The preprocessor program is called ecpg and is included in a normal PostgreSQL installation Embedded SQL programs are typically named with an extension pgc If you have a program file called prog1 pgc you can preprocess it by simply calling ecpg progl pgc This will create a file called prog1 c If your input files do not follow the suggested naming pattern you can specify the output file explicitly using the o option The preprocessed file can be compiled normally for example cc c progl c The generated C source files include headers files from the PostgreSQL installation so if you installed PostgreSQL in a location that is not searched by default you have to add an option such as I usr local pgsql include to the compilation command line To link an embedded SQL program you need to include t
267. iving the number of bytes of data returned If 1 is returned the caller must next call PQendcopy and then return to normal processing The data returned will not extend beyond a newline character If possible a whole line will be returned at one time But if the buffer offered by the caller is too small to hold a line sent by the backend then a partial data line will be returned This can be detected by testing whether the last returned byte is n or not The returned string is not null terminated If you want to add a terminating null be sure to pass a bufsize one smaller than the room actually available PQputline Sends a null terminated string to the backend server Returns 0 if OK EOF if unable to send the string int PQputline PGconn conn const char string 18 Chapter 1 libpq C Library Note the application must explicitly send the two characters on a final line to indicate to the backend that it has finished sending its data PQputnbytes Sends a non null terminated string to the backend server Returns 0 if OK Eor if unable to send the string int PQputnbytes PGconn conn const char buffer int nbytes This is exactly like POput line except that the data buffer need not be null terminated since the number of bytes to send is specified directly PQendcopy Synchronizes with the backend This function waits until the backend has finished the copy It should either be issued when the last string has be
268. ke the function known to PostgreSQL like this 245 Chapter 14 Interfacing Extensions To Indexes CREATE FUNCTION complex abs eq complex complex RETURNS boolean AS PGROOT src tutorial complex LANGUAGE C There are some important things that are happening here First note that operators for less than less than or equal equal greater than or equal and greater than for complex are being defined We can only have one operator named say and taking type complex for both operands In this case we don t have any other operator for complex but if we were building a practical data type we d probably want to be the ordinary equality operation for complex numbers In that case we d need to use some other operator name for complex abs eq Second although PostgreSQL can cope with operators having the same name as long as they have different input data types C can only cope with one global routine having a given name period So we shouldn t name the C function something simple like abs eq Usually it s a good practice to include the data type name in the C function name so as not to conflict with functions for other data types Third we could have made the PostgreSQL name of the function abs eq relying on PostgreSQL to distinguish it by input data types from any other PostgreSQL function of the same name To keep the example simple we make the function have the same names at the C level and PostgreSQL leve
269. l Finally note that these operator functions return Boolean values In practice all operators defined as index access method strategies must return type boolean since they must appear at the top level of a WHERE clause to be used with an index On the other hand support functions return whatever the particular access method expects in the case of the comparison function for B trees a signed integer Now we are ready to define the operators CREATE OPERATOR leftarg complex rightarg complex procedure complex abs eq restrict eqsel join eqjoinsel The important things here are the procedure names which are the C functions defined above and the restriction and join selectivity functions You should just use the selectivity functions used in the example see complex source Note that there are different such functions for the less than equal and greater than cases These must be supplied or the optimizer will be unable to make effective use of the index The next step is the registration of the comparison support routine required by B trees The C code that implements this is in the same file that contains the operator procedures CREATE FUNCTION complex abs cmp complex complex RETURNS integer AS PGROOT src tutorial complex LANGUAGE C 246 Chapter 14 Interfacing Extensions To Indexes 14 6 Creating the Operator Class Now that we have the requ
270. l len u un fact AS sl len cm FROM shoelace data s unit u WHERE s sl unit u un name CREATE VIEW shoe ready AS SELECT rsh shoename rsh sh avail rsl sl name rsl sl avail min rsh sh avail rsl sl avail AS total avail FROM shoe rsh shoelace rsl WHERE rsl sl_color rsh slcolor AND rsl sl_len_cm gt rsh slminlen_cm AND rsl sl len cm lt rsh slmaxlen_cm The CREATE VIEW command for the shoelace view which is the simplest one we have will create a relation shoelace and an entry in pg rewrite that tells that there is a rewrite rule that must be applied whenever the relation shoelace is referenced in a query s range table The rule has no rule qualification discussed later with the non SELECT rules since SELECT rules currently cannot have them and it is INSTEAD Note that rule qualifications are not the same as query qualifications The rule s action has a query qualification The rule s action is one query tree that is a copy of the SELECT statement in the view creation command Note The two extra range table entries for NEW and OLD named NEW and CURRENT for historical reasons in the printed query tree you can see in the pg rewrite entry aren t of interest for SELECT rules 221 Chapter 13 The Rule System Now we populate unit shoe data and shoelace data and Al types the first SELECT in his life
271. l number of tuples to be returned funcctx max calls PG GETARG UINT32 0 Build a tuple description for a __testpassbyval tuple 5 tupdesc RelationNameGetTupleDesc testpassbyval allocate a slot for a tuple with this tupdesc slot TupleDescGetSlot tupdesc assign slot to function context funcctx gt slot slot Generate attribute metadata needed later to produce tuples from raw C strings xy attinmeta TupleDescGetAttInMetadata tupdesc funcctx attinmeta attinmeta MemoryContextSwitchTo oldcontext stuff done on every call of the function funcctx SRF PERCALL SETUP call cntr funcctx call cntr max calls funcctx max calls slot funcctx gt slot attinmeta funcctx gt attinmeta if call_cntr lt max_calls do when there is more left to send char values HeapTuple tuple Datum result Prepare a values array for storage in our slot This should be an array of C strings which will be processed later by the appropriate in functions values char palloc 3 sizeof char values 0 char palloc 16 sizeof char 197 Chapter 9 Extending SQL Functions values 1 char palloc 16 sizeof char char palloc 16 sizeof char values 2 snprintf values 0 16 d 1 PG GETARG INT32 1 snprintf values 1 16 d 2 PG GETARG INT32 1 snprintf values 2 16 d
272. l pointers for the login and pwd parameters It is provided primarily for backward compatibility with old programs POconnectStart POconnectPoll Make a connection to the database server in a nonblocking man ner PGconn PQconnectStart const char conninfo PostgresPollingStatusType POQconnectPoll PGconn conn These two routines are used to open a connection to a database server such that your application s thread of execution is not blocked on remote I O whilst doing so The database connection is made using the parameters taken from the string conninfo passed to PQconnect Start This string is in the same format as described above for PQconnect db Neither PQconnectStart nor POconnectPoll will block as long as a number of restrictions are met The hostaddr and host parameters are used appropriately to ensure that name and reverse name queries are not made See the documentation of these parameters under PQconnectdb above for details If you call Pot race ensure that the stream object into which you trace will not block e You ensure for yourself that the socket is in the appropriate state before calling POconnectPoll as described below To begin call conn PQconnectStart connection info string If conn is NULL then libpq has been unable to allocate a new PGconn structure Otherwise a valid PGconn pointer is returned Chapter 1 libpq C Library though not yet representing a valid connection to the database On re
273. ld ones In the rule system it contains just the expressions from the SET attribute expression part of the query The planner will handle missing columns by inserting expressions that copy the values from the old row into the new one And it will add the special CTID entry just as for DELETE too Every entry in the target list contains an expression that can be a constant value a variable pointing to an attribute of one of the relations in the range table a parameter or an expression tree made of function calls constants variables operators etc 218 Chapter 13 The Rule System the qualification The query s qualification is an expression much like one of those contained in the target list en tries The result value of this expression is a Boolean that tells if the operation INSERT UPDATE DELETE or SELECT for the final result row should be executed or not It is the WHERE clause of an SQL statement the join tree The query s join tree shows the structure of the FROM clause For a simple query like SELECT FROM a b c the join tree is just a list of the FROM items because we are allowed to join them in any order But when JOIN expressions particularly outer joins are used we have to join in the order shown by the joins The join tree shows the structure of the JOIN expressions The restrictions associated with particular JOIN clauses from ON or USING expressions are stored as qualification expressions attached to thos
274. le indexCorrelation The first four parameters are inputs root The query being processed rel The relation the index is on 249 Chapter 15 Index Cost Estimation Functions index The index itself indexQuals List of index qual clauses implicitly ANDed a NIL list indicates no qualifiers are available The last four parameters are pass by reference outputs indexStartupCost Set to cost of index start up processing indexTotalCost Set to total cost of index processing indexSelectivity Set to index selectivity indexCorrelation Set to correlation coefficient between index scan order and underlying table s order Note that cost estimate functions must be written in C not in SQL or any available procedural language because they must access internal data structures of the planner optimizer The index access costs should be computed in the units used by src backend optimizer path costsize c a sequential disk block fetch has cost 1 0 a nonsequential fetch has cost random page cost and the cost of processing one index tuple should usually be taken as cpu index tuple cost which is a user adjustable optimizer parameter In addition an appropriate multiple of cpu operator cost should be charged for any comparison operators invoked during index processing especially evaluation of the indexQuals themselves The access costs should include all disk and CPU costs associated with scanning the index itself but NOT the
275. length types must begin with a length field of exactly 4 bytes and all data to be stored within that type must be located in the memory immediately following that length field The length field is the total length of the structure i e it includes the size of the length field itself We can define the text type as follows typedef struct int4 length char data 1 text Obviously the data field declared here is not long enough to hold all possible strings Since it s impossible to declare a variable size structure in C we rely on the knowledge that the C compiler won t range check array subscripts We just allocate the necessary amount of space and then access the array as if it were declared the right length If this isn t a familiar trick to you you may wish to spend some time with an introductory C programming textbook before delving deeper into PostgreSQL server programming When manipulating variable length types we must be careful to allocate the correct amount of memory and set the length field correctly For example if we wanted to store 40 bytes in a text structure we might use a code fragment like this include postgres h char buffer 40 our source data text destination text palloc VARHDRSZ 40 destination gt length VARHDRSZ 40 memcpy destination data buffer 40 VARHDRSZ is the same as sizeof int4 but it s considered good style to use the macro VARHDRSZ to refer to the size of the o
276. ler built in box BOX utils geo decls h bytea bytea postgres h char char compiler built in character BpChar postgres h cid CommandId postgres h date DateADT utils date h smallint int2 int2 or int16 postgres h int2vector int2vector postgres h integer int4 int4 or int32 postgres h real float4 float4 postgres h double precision float8 float8 postgres h 183 Chapter 9 Extending SQL Functions SQL Type C Type Defined In interval Interval utils timestamp h lseg LSEG utils geo decls h name IName postgres h oid Oid postgres h oidvector oidvector postgres h path PATH utils geo decls h point POINT utils geo_decls h regproc regproc postgres h reltime RelativeTime utils nabstime h text text postgres h tid ItemPointer storage itemptr h time TimeADT utils date h time with time zone TimeTzADT utils date h timestamp Timestamp utils timestamp h tinterval TimeInterval utils nabstime h varchar VarChar postgres h xid TransactionId postgres h Internally PostgreSQL regards a base type as a blob of memory The user defined functions that you define over a type in turn define the way that PostgreSQL can operate on it That is PostgreSQL will only store and retrieve the data from disk and use your user defined functions to input process and output the data Base types can have one of three internal formats pass by
277. les are compiled into object files then the object files are linked together The object files need to be created as position independent code PIC which conceptually means that they can be placed at an arbitrary location in memory when they are loaded by the executable Object files intended for executables are usually not compiled that way The command to link a shared library contains special flags to distinguish it from linking an executable At least this is the theory On some systems the practice is much uglier In the following examples we assume that your source code is in a file oo c and we will create a shared library oo so The intermediate object file will be called foo o unless otherwise noted A shared library can contain more than one object file but we only use one here 199 Chapter 9 Extending SQL Functions BSD OS The compiler flag to create PIC is pic The linker flag to create shared libraries is shared gcc fpic c foo c ld shared o foo so foo o This is applicable as of version 4 0 of BSD OS FreeBSD The compiler flag to create PIC is fpic To create shared libraries the compiler flag is shared gce fpic c foo c gcc shared o foo so foo o This is applicable as of version 3 0 of FreeBSD HP UX The compiler flag of the system compiler to create PIC is z When using GCC it s pic The linker flag for shared libraries is b So cc tz c foo c Or gcc fpic c foo c and then
278. lication code will typically use to acquire a pooled database connection The server interface is javax sql ConnectionPoolDataSource Which is how most ap plication servers will interface with the PostgreSQL JDBC driver In an application server environment the application server configuration will typically refer to the Post greSQL ConnectionPoolDataSource implementation while the application component code will typ ically acquire a Dat aSource implementation provided by the application server not by PostgreSQL In an environment without an application server PostgreSQL provides two implementations of Data Source Which an application can use directly One implementation performs connection pooling while the other simply provides access to database connections through the DataSource interface without any pooling Again these implementations should not be used in an application server environment unless the application server does not support the Connect ionPoolDataSource interface 5 9 3 Application Servers ConnectionPoolDataSource PostgreSQL includes one implementation of Connect ionPoolDataSource for JDBC 2 and one for JDBC 3 Table 5 1 ConnectionPoolDataSource Implementations JDBC Implementation Class 2 org postgresql jdbc2 optional ConnectionPool 3 org postgresql jdbc3 Jdbc3ConnectionPool Both implementations use the same configuration scheme JDBC requires that a Connect ionPoolData Source be configure
279. llContext and clearing any previously returned data left over from the previous pass If your function has data to return use SRFE RETURN NEXT funcctx result to return it to the caller The result must be a Datum either a single value or a tuple prepared as described earlier Finally when your function is finished returning data use SRE RETURN DONE funcctx to clean up and end the SRF The memory context that is current when the SRF is called is a transient context that will be cleared between calls This means that you do not need to p ree everything you palloc it will go away anyway However if you want to allocate any data structures to live across calls you need to put them somewhere else The memory context referenced by multi call memory ctx is a suitable location for any data that needs to survive until the SRF is finished running In most cases this means that you should switch into nulti call memory ctx while doing the first call setup A complete pseudo code example looks like the following Datum my Set Returning Function PG FUNCTION ARGS FuncCallContext funcctx Datum result MemoryContext oldcontext user defined declarations 195 if Chapter 9 Extending SQL Functions SRF_IS_FIRSTCALL funcctx SRF_FIRSTCALL_INIT oldcontext MemoryContextSwitchTo funcctx gt multi_call_memory_ctx one time setup code appears here user defined code if r
280. llow you to access a field as many times as you want You must close a ResultSet by calling close once you have finished using it Once you make another query with the Statement used to create a ResultSet the currently open ResultSet instance is closed automatically ResultSet is currently read only You can not update data through the ResultSet If you want to update data you need to do it the old fashioned way by issuing a SQL update statement This is in conformance with the JDBC specification which does not require drivers to provide this functionality 5 4 Performing Updates To change data perform an insert update or delete you use the executeUpdate method exe cuteUpdate is similar to the executeQuery used to issue a select however it doesn t return a ResultSet instead it returns the number of records affected by the insert update or delete statement Example 5 2 Simple Delete Example This example will issue a simple delete and print out the number of rows deleted int foovalue 500 1 Chapter 5 JDBC Interface PreparedStatement st db prepareStatement DELETE FROM mytable where colum nfoo st setInt 1 foovalue int rowsDeleted st executeUpdate System out println rowsDeleted rows deleted st close 5 5 Creating and Modifying Database Objects To create modify or drop a database object like a table or view you use the execute method ex
281. lo unlink conn lobjId Inputs conn Specifies a valid database connection lobjld Identifier for a large object Outputs None Description pg lo unlink deletes the specified large object Usage 63 pg lo import Name pg lo import import a large object from a file Synopsis pg lo import conn filename Inputs conn Specifies a valid database connection filename Unix file name Outputs None Description pg 1o import reads the specified file and places the contents into a large object Usage pg 1o import must be called within a BEGIN END transaction block 64 bg lo export Name pg lo export export a large object to a file Synopsis pg lo export conn lobjld filename Inputs conn Specifies a valid database connection lobjld Large object identifier filename Unix file name Outputs None Description pg lo export writes the specified large object into a Unix file Usage pg 1o export must be called within a BEGIN END transaction block 65 Chapter 4 ECPG Embedded SQL in C This chapter describes the embedded SQL package for PostgreSQL It works with C and C It was written by Linus Tolke 1inusGepact se and Michael Meskes lt meskes postgresql org gt Admittedly this documentation is quite incomplete But since this interface is standardized additional information can be found in many resources about SQL 4 1 The Concept An embe
282. ls are Di log with a it to the cli log or both is controlled by the SERVER MIN MESSAGES and CLIENT MIN M E level format variable EBUG write the message to the server log Loc write the message to the server higher priority INFO NOTICE and WARNING write the message to the server log and send ent with respectively higher priorities and EXCEPTION raise an error and abort the current transaction Whether error messages of a particular priority are reported to the client written to the server variables See the PostgreSQL Administrator s Guide for more information ESSAG ES configuration 329 Chapter 19 PL pgSQL SQL Procedural Language Inside the format string is replaced by the next optional argument s external representation Write 3 to emit a literal Note that the optional arguments must presently be simple variables not expressions and the format must be a simple string literal Examples RAISE NOTICE Calling cs create job v job id In this example the value of v job id will replace the in the string RAISE EXCEPTION Inexistent ID gt user id This will abort the transaction with the given error message 19 8 1 Exceptions PostgreSQL does not have a very smart exception handling model Whenever the parser planner optimizer or executor decide that a statement cannot be process
283. lumn CREATE TABLE images imgname text img bytea To insert an image you would use File file new File myimage gif FileInputStream fis new FileInputStream file PreparedStatement ps conn prepareStatement INSERT INTO images VALUES ps setString 1 file getName ps setBinaryStream 2 fis file length ps executeUpdate ps close fis close Here setBinaryStream transfers a set number of bytes from a stream into the column of type bytea This also could have been done using the setBytes method if the contents of the image was already in a byte Retrieving an image is even easier We use PreparedStatement here but the Statement class can equally be used PreparedStatement ps con prepareStatement SELECT img FROM images WHERE name ps setString 1 myimage gif ResultSet rs ps executeQuery if rs null while rs next byte imgBytes rs getBytes 1 use the stream in some way here rs close ps close Here the binary data was retrieved as an byte You could have used a Input St ream object instead Alternatively you could be storing a very large file and want to use the LargeObject API to store the file 83 img Chapter 5 JDBC Interface CREATE TABLE imagesLO imgname text imgOID OID To insert an image you would use All LargeObject API calls m
284. m isn t finished with this loop so it continues and applies the RETURN rule on it and we get UPDATE shoelace data SET sl name s sl name Sl avail int4pl s sl avail shoelace arrive arr quant sl color s sl color sl len s sl len 234 sl unit s sl unit FROM shoelace arrive shoelace arrive shoelace ok shoelace ok shoelace ok OLD shoelace ok NEW shoelace shoelace shoelace OLD shoelace NEW shoelace data showlace data shoelace OLD shoelace NEW shoelace data s unit u WHERE bpchareq s sl name showlace arrive arr name AND bpchareq shoelace data sl name s sl name Chapter 13 The Rule System Again an update rule has been applied and so the wheel turns on and we are in rewrite round 3 This time rule log_shoelace gets applied producing the extra parse tree INSERT INTO shoelace log SELECT S sl name int4pl s sl avail shoelace arrive arr quant current user current timestamp FROM hoelace ok OLD shoelace ok NEW hoelace shoelace shoelace OLD hoelace NEW shoelace data showlace data hoelace OLD shoelace NEW hoelace data s unit u hoelace data OLD shoelace data NEW hoelace log shoelace log S S S S S S S S WHERE bpchareq s sl name showlace arrive arr name AND bpchareq shoelace data sl name s sl name AND int4ne int4pl s sl avail shoelace arrive arr
285. me argv 3 set up the connection 4 conn PQsetdb NULL NULL NULL NULL database check to see that the backend connection was successfully made if PQstatus conn CONNECTION BAD fprintf stderr Connection to database s failed n database fprintf stderr Ss PQerrorMessage conn exit nicely conn res PQexec conn begin POclear res 39 x Chapter 2 Large Objects printf importing file s n in filename lobjOid importFile conn in filename lobjOid lo import conn in filename printf as large object d n lobjOid printf picking out bytes 1000 2000 of the large object n pickout conn 1objOid 1000 1000 printf overwriting bytes 1000 2000 of the large object with X s Mn overwrite conn lobjOid 1000 1000 printf exporting large object to file s n out filename exportFile conn lobjOid out filename lo export conn lobjOid out filename res PQexec conn end POCclear res POfinish conn exit 0 40 Chapter 3 pgtcl Tcl Binding Library 3 1 Introduction pgtcl is a Tcl package for client programs to interface with PostgreSQL servers It makes most of the functionality of libpq available to Tcl scripts This package was originally written by Jolly Chen Table 3 1 gives an overview over the commands available in pgtcl These commands are described further on subsequent page S T
286. me that your programming language functions are written in C The basic rules for building C functions are as follows 198 Chapter 9 Extending SQL Functions Use pg config includedir server to find out where the PostgreSQL server header files are installed on your system or the system that your users will be running on This option is new with PostgreSQL 7 2 For PostgreSQL 7 1 you should use the option includedir pg config will exit with a non zero status if it encounters an unknown option For releases prior to 7 1 you will have to guess but since that was before the current calling conventions were introduced it is unlikely that you want to support those releases When allocating memory use the PostgreSQL routines palloc and pfree instead of the corresponding C library routines malloc and free The memory allocated by pa11oc will be freed automatically at the end of each transaction preventing memory leaks Always zero the bytes of your structures using memset or bzero Several routines such as the hash access method hash join and the sort algorithm compute functions of the raw bits contained in your structure Even if you initialize all fields of your structure there may be several bytes of alignment padding holes in the structure that may contain garbage values Most of the internal PostgreSQL types are declared in post gres h while the function manager inter faces PG FUNCTION ARGS etc are in fmgr h
287. ming that the result of the join operator must be false So it never makes sense to specify HASHES for operators that do not represent equality In fact logical equality is not good enough either the operator had better represent pure bitwise equality because the hash function will be computed on the memory representation of the values regardless of what the bits mean For example equality of time intervals is not bitwise equality the interval equality 212 Chapter 11 Extending SQL Operators operator considers two time intervals equal if they have the same duration whether or not their endpoints are identical What this means is that a join using between interval fields would yield different results if implemented as a hash join than if implemented another way because a large fraction of the pairs that should match will hash to different values and will never be compared by the hash join But if the optimizer chose to use a different kind of join all the pairs that the equality operator says are equal will be found We don t want that kind of inconsistency so we don t mark interval equality as hashable There are also machine dependent ways in which a hash join might fail to do the right thing For example if your data type is a structure in which there may be uninteresting pad bits it s unsafe to mark the equality operator HASHES Unless perhaps you write your other operators to ensure that the unused bits are always zero Anoth
288. n Type list List of tables in connected database Description Although you can do this with a simple select it is added here for convenience 143 get attnames Name get attnames return the attribute names of a table Synopsis get attnames table Parameters table name of table Return Type dictionary The dictionary s keys are the attribute names the values are the type names of the attributes Description Given the name of a table digs out the set of attribute names and types 144 get Name get get a tuple from a database table Synopsis get table arg keyname Parameters table Name of table arg Either a dictionary or the value to be looked up keyname Name of field to use as key optional Return Type dictionary A dictionary mapping attribute names to row values Description This method is the basic mechanism to get a single row It assumes that the key specifies a unique row If keyname is not specified then the primary key for the table is used If arg is a dictionary then the value for the key is taken from it and it is modified to include the new values replacing existing values where necessary The OID is also put into the dictionary but in order to allow the caller to work with multiple tables the attribute name is munged to make it unique It consists of the string oid followed by the name of the table 145 insert Name insert
289. n from the pool might look like this Note that it is critical that the connections are closed or else the pool will leak connections and eventually lock all the clients out Connection con null try con source getConnection use connection catch SQLException e log error finally if con null try con close catch SQLException e 5 9 5 DataSources and JNDI All the Connect ionPoolDataSource and DataSource implementations can be stored in JNDI In the case of the non pooling implementations a new instance will be created every time the object is retrieved from JNDI with the same settings as the instance which was stored For the pooling implementations the same instance will be retrieved as long as it is available e g not a different JVM retrieving the pool from JNDD or a new instance with the same settings created otherwise In the application server environment typically the application server s DataSource instance will be stored in JNDI instead of the PostgreSQL Connect ionPoolDataSource implementation In an application environment the application may store the DataSource in JNDI so that it doesn t have to make a reference to the DataSource available to all application components that may need to use it Example 5 7 DataSource JNDI Code Example Application code to initialize a pooling DataSource and add it to JNDI might look like this Jdbc3PoolingDataSource source ne
290. n is single threaded One implication of this architecture is that the postmaster and the backend always run on the same machine the database server while the frontend application may run anywhere You should keep this in mind because the files that can be accessed on a client machine may not be accessible or may only be accessed using a different path name on the database server machine You should also be aware that the postmaster and postgres servers run with the user ID of the PostgreSQL superuser Note that the PostgreSQL superuser does not have to be any particular user e g a user named post gres although many systems are installed that way Furthermore the PostgreSQL superuser should definitely not be the Unix superuser root It is safest if the PostgreSQL superuser is an ordinary unprivileged user so far as the surrounding Unix system is concerned In any case all files relating to a database should belong to this Postgres superuser 170 Chapter 8 Extending SQL An Overview In the sections that follow we will discuss how you can extend the PostgreSQL SQL query language by adding functions data types Operators aggregates 8 1 How Extensibility Works PostgreSQL is extensible because its operation is catalog driven If you are familiar with standard rela tional systems you know that they store information about databases tables columns etc in what are commonly known as system catalogs Some systems
291. nal the trigger man ager to skip the rest of the operation for this row ie subsequent triggers are not fired and the IN SERT UPDATE DELETE does not occur for this row If a non NULL value is returned then the op eration proceeds with that row value Note that returning a row value different from the original value of NEW alters the row that will be inserted or updated It is possible to replace single values directly in NEW and return that or to build a complete new record row to return The return value of a trigger fired AFTER is ignored it may as well always return a NULL value But an AFTER trigger can still abort the operation by raising an error Example 19 1 A PL pgSQL Trigger Procedure Example This example trigger ensures that any time a row is inserted or updated in the table the current user name and time are stamped into the row And it ensures that an employee s name is given and that the salary is a positive value CREATE TABLE emp empname text salary integer last date timestamp 351 Chapter 19 PL pgSQL SQL Procedural Language last user text CREATE FUNCTION emp stamp RETURNS TRIGGER AS BEGIN Check that empname and salary are given IF NEW empname ISNULL THEN RAISE EXCEPTION empname cannot be NULL value END IF IF NEW salary ISNULL THE RAISE EXCEPTION cannot have NULL salary NEW empname END IF Who works fo
292. nderlying socket id used to connect to the database This is useful for use in select calls etc 131 getnotify Name getnotify get the last notify from the server Synopsis getnotify Parameters none Return Type tuple None Last notify from server Exceptions TypeError Too many any arguments pg error Invalid connection Description getnotify method tries to get a notify from the server from the SQL statement NOTIFY If the server returns no notify the methods returns None Otherwise it returns a tuple couple relname pid where relname is the name of the notify and pid the process id of the connection that triggered the notify Remember to do a listen query first otherwise get notify will always return None 132 inserttable Name inserttable inserta list into a table Synopsis inserttable table values Parameters table The table name string values The list of rows values to insert list Return Type none Exceptions TypeError Bad argument type or too many any arguments pg error Invalid connection Description inserttable method allows to quickly insert large blocks of data in a table it inserts the whole values list into the given table The list is a list of tuples lists that define the values for each inserted row The rows values may contain string integer long or double real values Be very careful this method does not ty
293. ned above 22 2 Trigger Functions When a function is used in a trigger the dictionary TD contains trigger related values The trigger rows are in TD new and or TD old depending on the trigger event TD event contains the event as a string INSERT UPDATE DELETE Or UNKNOWN TD when contains one of BEFORE AFTER and H 1 http www python org 356 Chapter 22 PL Python Python Procedural Language UNKNOWN TD level contains one of ROW STATEMENT and UNKNOWN TD name contains the trigger name and TD relid contains the relation ID of the table on which the trigger occurred If the trigger was called with arguments they are available in TD args 0 to TD args n 1 If the TD when is BEFORE you may return None or OK from the Python function to indicate the row is unmodified SKIP to abort the event or MODIFY to indicate you ve modified the row 22 3 Database Access The PL Python language module automatically imports a Python module called pipy The functions and constants in this module are available to you in the Python code as plpy foo At present plpy implements the functions plpy debug msg plpy log msg plpy info msg plpy notice msg plpy warning msg plpy error msg and plpy fatal msg They are mostly equivalent to calling elog LEVEL msg from C code plpy error and plpy fatal actually ra
294. nfortunately there is no such thing as a standard RDBMS Therefore ecpg tries to understand syntax extensions as long as they do not create conflicts with the standard The following list shows all the known incompatibilities If you find one not listed please notify the developers Note however that we list only incompatibilities from a preprocessor of another RDBMS to ecpg and not ecpg features that these RDBMS do not support Syntax of FETCH The standard syntax for FETCH is FETCH direction amount IN FROM cursor Oracle however does not use the keywords IN or FROM This feature cannot be added since it would create parsing conflicts 4 11 For the Developer This section explain how ecpg works internally This information can occasionally be useful to help users understand how to use ecpg 4 11 1 The Preprocessor The first four lines written by ecpg to the output are fixed lines Two are comments and two are include lines necessary to interface to the library Then the preprocessor reads through the file and writes output Normally it just echoes everything to the output When it sees an EXEC SQL statement it intervenes and changes it The command starts with exec sql and ends with Everything in between is treated as an SQL statement and parsed for variable substitution 74 Chapter 4 ECPG Embedded SQL in C Variable substitution occurs when a symbol starts with a colon The variable
295. ng the columns as we did above is irrelevant to the system You must typecast the expressions to match the definition of the composite type or you will get errors like this ERROR function declared to return emp returns varchar instead of text at column 1 A function that returns a row composite type can be used as a table function as described below It can also be called in the context of an SQL expression but only when you extract a single attribute out of the row Or pass the entire row into another function that accepts the same composite type For example SELECT new emp name We need the extra parentheses to keep the parser from getting confused SELECT new emp name ERROR parser parse error at or near Another option is to use functional notation for extracting an attribute The simple way to explain this is that we can use the notations attribute table and table attribute interchangeably SELECT name new emp this is the same as SELECT EMP name AS youngster FROM EMP WHERE EMP age lt 30 SELECT name EMP AS youngster FROM EMP 178 Chapter 9 Extending SQL Functions WHERE age EMP 30 youngster Another way to use a function returning a row result is to declare a second function accepting a row type parameter and pass the function result to it CREATE FUNCTION getname
296. ngful when the trigger is BEFORE and FOR EACH ROW otherwise the return value is ignored Here s a little example trigger procedure that forces an integer value in a table to keep track of the number of updates that are performed on the row For new rows inserted the value is initialized to 0 and then incremented on every update operation CREATE FUNCTION trigfunc modcount RETURNS TRIGGER AS switch TG op INSERT set NEW 1 0 UPDATE set NEW 1 OLD 1 incr NEW 1 350 Chapter 20 PL Tcl Tcl Procedural Language default return OK return array get NEW LANGUAGE pltcl CREATE TABLE mytab num integer description text modcnt integer CREATE TRIGGER trig mytab modcount BEFORE INSERT OR UPDATE ON mytab FOR EACH ROW EXECUTE PROCEDURE trigfunc modcount modcnt Notice that the trigger procedure itself does not know the column name that s supplied from the trigger arguments This lets the trigger procedure be re used with different tables 20 2 6 Modules and the unknown command PL Tcl has support for auto loading Tcl code when used It recognizes a special table pltc1 modules which is presumed to contain modules of Tcl code If this table exists the module unknown is fetched from the table and loaded into the Tcl interpreter immediately after creating the interpreter While the unknown module could
297. nnect creates a new memory context and makes it current SPI finish restores the previous current memory context and destroys the context created by SPI connect These actions ensure that transient memory allocations made inside your procedure are reclaimed at procedure exit avoiding mem ory leakage However if your procedure needs to return an allocated memory object such as a value of a pass by reference data type you can t allocate the return object using palloc at least not while you are con nected to SPI If you try the object will be deallocated during SPI finish and your procedure will not work reliably To solve this problem use SPI palloc to allocate your return object SPI palloc allocates space from upper Executor memory that is the memory context that was current when SPI connect was called which is precisely the right context for return values of your procedure If called while not connected to SPI SPI palloc acts the same as plain palloc Before a procedure connects to the SPI manager the current memory context is the upper Executor con text so all allocations made by the procedure via palloc or by SPI utility functions are made in this context After SPI connect is called the current context is the procedure s private context made by SPI connect All allocations made via palloc repalloc or by SPI utility functions except for SPI copytuple SPI copytupledesc SPI copytupleintoslot SPI modifytuple and SPI
298. nt proc SPI processed If this is SELECT and some tuple s fetched returns tuples to the caller via elog INFO KY if ret SPI OK SELECT amp amp SPI processed gt 0 TupleDesc tupdesc SPI_tuptable gt tupdesc SPITupleTable tuptable SPI tuptable char buf 8192 int i 300 Chapter 17 Server Programming Interface for j 0 j lt proc j HeapTuple tuple tuptable vals j for i 1 buf 0 0 i lt tupdesc natts i snprintf buf strlen buf sizeof buf strlen buf s s SPI_getvalue tuple tupdesc i i tupdesc gt natts qms elog INFO EXECQ s buf SPI_finish pfree query return proc Now compile and create the function CREATE FUNCTION execq text integer RETURNS integer AS path to so LANGUAGE C vac SELECT execq CREATE TABLE a x INTEGER 0 execq 0 1 row vac INSERT INTO a VALUES execq INSERT INTO a VALUES 0 0 INSERT 167631 1 vac SELECT execq SELECT FROM a 0 INFO EXECQ 0 lt lt lt inserted by execq INFO EXECQ 1 lt lt lt value returned by execq and inserted by upper INSERT execq 2 1 row vac SELECT execq INSERT INTO a SELECT x 2 FROM a 1 execq 1 1 row vac S
299. nt 150 Petes Ub ses icc cr erac e e ted ei eec ctr E de ete 150 dictresult eintiene a aen bunten 151 listtieldsz i uet dar uu aid ects 152 fieldn ime s iiie A duni 153 fieldinim seen ient 154 ntuples itu Asch naa p d npe ES 155 6 6 Large Object pglatge uscetenmeeg mre QUIPPE GENUS 156 PED oed mt P REC ORE RERO EE 156 Close T tet boc Mohan etc mes ee telis 158 up en A I eI A 159 Ludi ET 160 seek ascen es Se ak a E moin 161 Jim HE 162 NE oo coer hha en ina Aa ne ans 163 d 164 eXDOFL nuc tenis E I M a Mr e IA cu 165 TI Server Programming RRPRRRRRR 166 T Architectut ss anode ien te Hei Gib hen Mile Ra aia le ce eee aider 168 7 1 PostgreSQL Architectural Concepts ennemi 168 8 Extending SQL An Overview ssesseseeeseeeeeee nennen nennen innen nenne etneen tenerte enne nennen 171 8 1 How Extensibility Works 4 4 iet eet tette ede hu te to eiat 171 vi 8 2 The PostgreSQL Type System eren nennen ener 171 8 3 About the PostgreSQL System Catalogs esee 171 9 Extending SQL Functions eese esee tenete enne te eter tenete teinte treten 175 9 T IntrodUctiOmQ 4 ere tee d ege e e e E E A ise orbe recon 175 9 2 Query Language SQL Functions eseseeeeeee eene enne nnne nene nnnen tenent 175 9 2 Examples 65 eee ei pe er a italie SUR PERRO HERRERA 175 9 2 2 SQ
300. ntaxError Too many arguments Description get defopt returns the current default connection options specification or None if the environment variables should be used Environment variables will not be looked up 121 set defopt Name set defopt set default options specification DV Synopsis set defopt options Parameters options New default connection options string None Return Type string or None Previous default opt specification Exceptions TypeError Bad argument type or too many arguments Description set defopt sets the default connection options value for new connections If None is supplied as parameter environment variables will be used in future connections It returns the previous setting for default options 122 get deftty Name get deftty get default connection debug terminal specification DV Synopsis get deftty Parameters none Return Type string or None Default debug terminal specification Exceptions SyntaxError Too many arguments Description get deftty returns the current default debug terminal specification or None if the environment vari ables should be used Environment variables will not be looked up 123 set deftty Name set deftty set default connection debug terminal specification DV Synopsis set deftty terminal Parameters terminal New default debug terminal string None Ret
301. null true if TRIGGER FIRED BEFORE trigdata gt tg_event when before else when after tupdesc trigdata gt tg_relation gt rd_att Connect to SPI manager if ret SPI_connect lt 0 elog INFO trigf fired s SPI_connect returned d when ret Get number of tuples in relation ret SPI exec SELECT count FROM ttest 0 if ret lt 0 elog NOTICE trigf fired s SPI exec returned d when ret count returns int8 as of PG 7 2 so be careful to convert i int DatumGetInt64 SPI getbinval SPI tuptable vals 0 SPI tuptable tupdesc 1 amp isnull elog NOTICE trigf fired s there are d tuples in ttest when i SPI finish if checknull void SPI getbinval rettuple tupdesc 1 amp isnull if isnull rettuple NULL return PointerGetDatum rettuple Now compile and create the trigger function CR CR EATE FUNCTION trigf RETURNS TRIGGER AS path to so LANGUAGE C EATE TABLE ttest x int4 257 Chapter 16 Triggers vac CREATE TRIGGER tbefore BEFORE INSERT OR UPDATE OR DELETE ON ttest FOR EACH ROW EXECUTE PROCEDURE trigf CREATE vac
302. num lt 0 or gt number of attributes in tuple 292 SPI modifytuple Description SPI modifytuple creates a new tuple by substituting new values for selected attributes copying the original tuple s attributes at other positions The input tuple is not modified Usage If successful a pointer to the new tuple is returned The new tuple is allocated in upper Executor context 293 SPI palloc Name SPI palloc Allocates memory in upper Executor context Synopsis SPI palloc size Inputs Size size Octet size of storage to allocate Outputs void New storage space of specified size Description SPI palloc allocates memory in upper Executor context Usage TBD 294 SPI repalloc Name SPI repalloc Re allocates memory in upper Executor context Synopsis SPI repalloc pointer size Inputs void pointer Pointer to existing storage Size size Octet size of storage to allocate Outputs void New storage space of specified size with contents copied from existing area Description SPI repalloc re allocates memory in upper Executor context Usage This function is no longer different from plain repalloc It s kept just for backward compatibility of existing code 295 SPI pfree Name SPI pfree Frees memory in upper Executor context Synopsis SPI pfree pointer Inputs void pointer Pointer to existing storage Outputs None Description SPI
303. o connect to If this begins with a slash it specifies Unix domain communication rather than TCP IP communication the value is the name of the directory in which the socket file is stored The default is to connect to a Unix domain socket in tmp hostaddr IP address of host to connect to This should be in standard numbers and dots form as used by the BSD functions inet atonetal If a nonzero length string is specified TCP IP communication is used Using hostadar instead of host allows the application to avoid a host name look up which may be important in applications with time constraints However Kerberos authentication requires the host name The following therefore applies If host is specified without hostaddr a host name lookup is forced If hostaddr is specified without host the value for hostaddr gives the re mote address if Kerberos is used this causes a reverse name query If both host and hostaddr are specified the value for hostaddr gives the remote address the value for host is ignored unless Kerberos is used in which case that value is used for Kerberos authentication Note that authentication is likely to fail if libpq is passed a host name that is not the name of the machine at hostaddr Without either a host name or host address libpq will connect using a local Unix domain socket port Port number to connect to at the server host or socket file name extension for Unix domain con nections dbname The data
304. o run it rv plpy execute plan name 5 The limit argument is optional in the call to plpy execute In the current version any database error encountered while running a PL Python function will result in the immediate termination of that function by the server it is not possible to trap error conditions using Python try catch constructs For example a syntax error in an SQL statement passed to the plpy execute call will terminate the function This behavior may be changed in a future release 357 Chapter 22 PL Python Python Procedural Language When you prepare a plan using the PL Python module it is automatically saved Read the SPI documen tation Chapter 17 for a description of what this means In order to make effective use of this across function calls one needs to use one of the persistent storage dictionaries SD or GD see Section 22 1 For example CREATE FUNCTION usesavedplan RETURNS TRIGGER AS if SD has key plan plan SD plan else plan plpy prepare SELECT 1 SD plan plan rest of function LANGUAGE plpython 22 4 Restricted Environment The current version of PL Python functions as a trusted language only access to the file system and other local resources is disabled Specifically PL Python uses the Python restricted execution environment further restricts it to prevent the use of the file open call and allows only modules f
305. objects and LargeObject which deals with an individual object 5 7 3 1 Class orzg postgresql largeobject LargeObject public class LargeObject extends Object java lang Object l t org postgresql largeobject LargeObject This class implements the large object interface to PostgreSQL It provides the basic methods required to run the interface plus a pair of methods that provide Input Stream and Output Stream classes for this object 103 Chapter 5 JDBC Interface Normally client code would use the methods in BLOB to access large objects However sometimes lower level access to Large Objects is required that is not supported by the JDBC specification Refer to org postgresql largeobject LargeObjectManager on how to gain access to a Large Object or how to create one See Also LargeObjectManager 5 7 3 1 1 Variables public static final int SEEK_SET Indicates a seek from the beginning of a file public static final int SEEK_CUR Indicates a seek from the current position public static final int SEEK_END Indicates a seek from the end of a file 5 7 3 1 2 Methods public int getOID Returns the OID of this LargeObject public void close throws SQLException This method closes the object You must not call methods in this object after this is called public byte read int len throws SOLException Reads some data from the object and return as a byte array public int read byte
306. obtained by dividing these quantities Average is typically implemented by using a two element array as the transition state value For example the built in implementation of avg float8 looks like 215 Chapter 12 Extending SQL Aggregates CREATE AGGREGATE avg sfunc float8 accum basetype float8 stype float8 finalfunc float8_avg initcond 0 0 For further details see the description of the CREATE AGGREGATE command in the Reference Manual 216 Chapter 13 The Rule System Author Written by Jan Wieck Updates for 7 1 by Tom Lane 13 1 Introduction Production rule systems are conceptually simple but there are many subtle points involved in actually using them Some of these points and the theoretical foundations of the PostgreSQL rule system can be found in On Rules Procedures Caching and Views in Database Systems Some other database systems define active database rules These are usually stored procedures and triggers and are implemented in PostgreSQL as functions and triggers The query rewrite rule system the rule system from now on is totally different from stored procedures and triggers It modifies queries to take rules into consideration and then passes the modified query to the query planner for planning and execution It is very powerful and can be used for many things such as query language procedures views and versions The power of this rule system i
307. od and is supplied as the C API uses unlink 5 8 Using the driver in a multithreaded or a servlet environment A problem with many JDBC drivers is that only one thread can use a Connection at any one time otherwise a thread could send a query while another one is receiving results and this would be a bad thing for the database engine The PostgreSQL JDBC Driver is thread safe Consequently if your application uses multiple threads then you do not have to worry about complex algorithms to ensure that only one uses the database at any time If a thread attempts to use the connection while another one is using it it will wait until the other thread has finished its current operation If it is a regular SQL statement then the operation consists of sending the statement and retrieving any ResultSet in full If itis a Fastpath call e g reading a block from a LargeOb ject then it is the time to send and retrieve that block This is fine for applications and applets but can cause a performance problem with servlets With servlets you can have a heavy load on the connection If you have several threads performing queries then each but one will pause which may not be what you are after To solve this you would be advised to create a pool of connections When ever a thread needs to use the database it asks a manager class for a Connection The manager hands a free connection to the thread and marks it as busy If a free connection is not a
308. omp manufidx on computer Index Scan using soft hostidx on software resulting from the rules query DELETE FROM software WHERE computer manufacurer bim AND software hostname computer hostname In any of these cases the extra queries from the rule system will be more or less independent from the number of affected rows in a query Another situation is cases on UPDATE where it depends on the change of an attribute if an action should be performed or not In PostgreSQL version 6 4 the attribute specification for rule events is disabled it will have its comeback latest in 6 5 maybe earlier stay tuned So for now the only way to create a rule as in the shoelace log example is to do it with a rule qualification That results in an extra query that is performed always even if the attribute of interest cannot change at all because it does not appear in the target list of the initial query When this is enabled again it will be one more advantage of rules over triggers Optimization of a trigger must fail by definition in this case because the fact that its actions will only be done when a specific attribute is updated is hidden in its functionality The definition of a trigger only allows to specify it on row level so whenever a row is touched the trigger must be called to make its decision The rule system will know it by looking up the target list and will suppress the additional query completely if the attri
309. on receives an integer and increments it by one returning the incremented value CREATE FUNCTION add one integer RETURNS INTEGER AS BEGIN RETURN 1 1 332 Chapter 19 PL pgSQL SQL Procedural Language END LANGUAGE plpgsql Example 19 3 A Simple PL pgSQL Function to Concatenate Text This function receives two text parameters and returns the result of concatenating them CREATE FUNCTION concat text TEXT TEXT RETURNS TEXT AS BEGIN RETURN 1 2 END LANGUAGE plpgsql Example 19 4 A PL pgSQL Function on Composite Type In this example we take EMP a table and an integer as arguments to our function which returns a boolean Ifthe salary field of the Emp table is NULL we return Otherwise we compare with that field with the integer passed to the function and return the boolean result of the comparison t or f This is the PL pgSQL equivalent to the example from the C functions CREATE FUNCTION c overpaid EMP INTEGER RETURNS BOOLEAN AS DECLARE emprec ALIAS FOR 1 sallim ALIAS FOR 2 BEGI IF emprec salary ISNULL THEN RETURN f END IF RETURN emprec salary sallim END LANGUAGE plpgsql 19 11 Porting from Oracle PL SQL Author Roberto Mello lt rmello fslc usu edu gt This section explains differences between Oracle s
310. onn COMMIT POclear res close the connection to the database and cleanup POfinish conn fclose debug return 0 Example 1 2 libpq Example Program 2 testlibpq2 c Test of the asynchronous notification interface Start this program then from psql in another window do NOTIFY TBL2 Or if you want to get fancy try this Populate a database with the following pi CREATE TABLE TBL1 i int4 K CREATE TABLE TBL2 i int4 E CREATE RULE rl AS ON INSERT TO TBL1 DO e INSERT INTO TBL2 values new i NOTIFY TBL2 and do x INSERT INTO TBL1 values 10 o include lt stdio h gt include libpq fe h 26 Chapter 1 libpq C Library void exit nicely PGconn conn POfinish conn exit 1 main char pghost pgport pgoptions pgtty char dbName int nFields int a ji PGconn conn PGresult res PGnotify notify begin by setting the parameters for a backend connection if the parameters are null then the system will try to use reasonable defaults by looking up environment variables or failing that using hardwired constants f pghost NULL host name of the backend server pgport NULL port of the backend server pgoptions NULL special options to start up the backend server pgtty NULL debugging tty for the backend serv
311. onn conn Chapter 1 libpq C Library POtty Returns the debug tty of the connection char PQtty const PGconn conn PQoptions Returns the backend options used in the connection char PQoptions const PGconn conn PQstatus Returns the status of the connection ConnStatusType PQstatus const PGconn conn The status can be one of a number of values However only two of these are seen outside of an asyn chronous connection procedure CONNECTION OK or CONNECTION BAD A good connection to the database has the status CONNECTION CK A failed connection attempt is signaled by status CONNEC TION BAD Ordinarily an OK status will remain so until PO inish but a communications failure might result in the status changing to CONNECTION BAD prematurely In that case the application could try to recover by calling POreset See the entry for PQconnect Start and POconnectPo11 with regards to other status codes that might be seen PQerrorMessage Returns the error message most recently generated by an operation on the connec tion char PQerrorMessage const PGconn conn Nearly all libpq functions will set PQerrorMessage if they fail Note that by libpq convention a non empty PQerrorMessage will include a trailing newline PQbackendP ID Returns the process ID of the backend server handling this connection int PQbackendPID const PGconn conn The backend PID is useful for debugging purposes and for comparison to N
312. ons in a qualification expression Since SQL representations of query trees are sufficient to understand the rule system this document will not teach how to read them It might help to learn it and the naming conventions are required in the later following descriptions 217 Chapter 13 The Rule System 13 2 1 The Parts of a Query tree When reading the SQL representations of the query trees in this document it is necessary to be able to identify the parts the statement is broken into when it is in the query tree structure The parts of a query tree are the command type This is a simple value telling which command SELECT INSERT UPDATE DELETE produced the parse tree the range table The range table is a list of relations that are used in the query In a SELECT statement these are the relations given after the FROM keyword Every range table entry identifies a table or view and tells by which name it is called in the other parts of the query In the query tree the range table entries are referenced by index rather than by name so here it doesn t matter if there are duplicate names as it would in an SQL statement This can happen after the range tables of rules have been merged in The examples in this document will not have this situation the result relation This is an index into the range table that identifies the relation where the results of the query go SELECT queries normally don t have a result relation The special case
313. onseae EE apr PURO EE DE eO dH 57 pg3lo el088 5 Sete pate eer RENE eee Qe PW SERRE EUR 58 PS AO read oue SE ono om Het eet ee EAE 59 pg lO wtltes iue aeter tetro cete ea aus eee EXER GER ERR CEP E EE ESTEE Ue CNN 60 p loli qe EE 61 pg AO ell echelon ae es et a i ae ee eee 62 Pe lo unlink sss s oir t so ORE RR IE ET ee 63 pg lo nnpott i i ede ee HS ate o a n e ete eode 64 pe Jo export 4 oS rtt PO D a PUE egi iste 65 4 ECPG Embedded SQE 1n Cenci ie ee bete ee tacente eb e iere bte 66 4T The Concept oso eo eee teo reo duit ed Rn 66 4 2 Connecting to the Database Server eren eren 66 4 3 Closing a Connection nee ette eere rt ie Or e e tatit 67 4 4 Running SQL Commandis essent E nennen nene enne nenne 67 4 5 Passing D AI EE ve eei tmu et es E EU E tpe ERE 68 4 6 Error Handling eU cte Ue tete ett oco Ue a A ete ie 69 awPSrdnipaddlsce pP pp 72 4 8 Processing Embedded SQL Programs eene 73 4 9 Library Functions s 03 0 io ciency ania tied an oe ee penale dep 73 4 10 Porting From Other RDBMS Packages essere eee enne 74 4 V1 For the Developet nee et ertet reete tette rte iet YI ER eee ee epe eR Eee dS 74 4 TTA The Preprocessor orco EE A A A E EEE 74 42 The Library eene Re oe hae 76 92 JDBGntertace cesses case sive Etats em ER m nie alte into tte tied TT 5 1 Setting up the JDBC Driver rennen nennen nnne enne nennen enne TI Sell Gettin
314. open at one time One reason to do that is to access more than one database Each connection is represented by a PGconn object which is obtained from PQconnectdb or POset dbLogin Note that these functions will always return a non null object pointer unless perhaps there is too little memory even to allocate the PGconn object The POstatus function should be called to check whether a connection was successfully made before queries are sent via the connection object PQconnectdb Makes a new connection to the database server PGconn PQconnectdb const char conninfo This routine opens a new database connection using the parameters taken from the string conninfo Unlike POsetdbLogin below the parameter set can be extended without changing the function signa ture so use either of this routine or the nonblocking analogues PQconnect Start and POconnectPoll is preferred for application programming The passed string can be empty to use all default parameters or it can contain one or more parameter settings separated by whitespace Each parameter setting is in the form keyword value To write an empty value or a value con taining spaces surround it with single quotes e g keyword a value Single quotes and back slashes within the value must be escaped with a backslash e g or Spaces around the equal sign are optional The currently recognized parameter keywords are Chapter 1 libpq C Library host Name of host t
315. oping Through Query Results seseeeeeeeeeeeeneen nene 325 19 7 CUESOIS fere tee e iade erede ee pdt eet e ode 326 19 7 1 Declaring Cursor Variables sess 326 19 7 2 Opening Cursors ree tete ete ote ds e Ee eredi 327 19 7 2 1 OREN FOR SELECT getestet ERE 327 19 72 25 OPEN FOR EXECUTE anere tette i eres 327 19 7 2 3 Opening a bound cursor seen 327 19 7 3 Using CUISOTS eniti pe ir e tet etie e a ei ET 327 19 73 FETCH ie Rr RP RP RE RET 328 1977532 CLOSE iet ies ie tebiptde teen pee 328 19 7 3 3 Returning Cursots sssi reseso isset ert eee nre e Ete e s ceat 328 19 8 Errors and Messages uteo niteretur dee tip diee 329 19 8 Jt Exceptions i ete de imer eet eerie eerie E Sanson 330 19 9 Trigger Procedures ceo ehe epas Ie SR Ea Ras IiE Eoste SEEE Si 330 19 10 Examples es reet e e ee eMe EE EEE AE 332 19 11 Porting from Oracle PL SQL i ettet terere 333 19 11 1 Main Differences eter EE ETE ERU PER dade 333 19 11 1 1 Quote Me on That Escaping Single Quotes ss 334 19 112 Porting Functions etr mee eec tient eie evite cendi 335 19 11 3 Procedutes enean te re DOOR D dE 339 19 11 4 Packages Ree ert den PUER Iter e eie gig Ere eis 340 19 11 5 Other Things to Watch For essere ener 341 19 T5 EXECUTE vos ine et ir ce rr ties 342 19 11 5 2 Optimizing PL pgSQL Functions
316. or JDBC 3 The pooling implementations do not actually close connections when the client calls the c1ose method but instead return the connections to a pool of available connections for other clients to use This avoids any overhead of repeatedly opening and closing connections and allows a large number of clients to share a small number of database connections The pooling datasource implementation provided here is not the most feature rich in the world Among other things connections are never closed until the pool itself is closed there is no way to shrink the pool As well connections requested for users other than the default configured user are not pooled Many application servers provide more advanced pooling features and use the Connect ionPoolDataSource implementation instead Table 5 3 DataSource Implementations JDBC Pooling Implementation Class 2 INo org postgresql jdbc2 optio 2 Yes org postgresql jdbc2 optio 3 INO org postgresql jdbc3 Jdbc3 109 nal SimpleDat nal PoolingDa SimpleDataSou Chapter 5 JDBC Interface JDBC Pooling Implementation Class Yes org postgresql jdbc3 Jdbc3 All the implementations use the same configuration scheme JDBC requires that a DataSource be con figured via JavaBean properties so there are get and set methods for each of these properties Table 5 4 DataSource Configuration Properties Prop
317. orm available at the projects web site http www postgresqlorg Entering a bug report this way causes it to be mailed to the lt pgsql bugs postgresql org gt mailing list Do not send bug reports to any of the user mailing lists such as lt pgsql sql postgresql org gt or lt pgsql general postgresql org gt These mailing lists are for answering user questions and their subscribers normally do not wish to receive bug reports More importantly they are unlikely to fix them Also please do not send reports to the developers mailing list lt pgsql hackers postgresql org gt This list is for discussing the development of PostgreSQL and it would be nice if we could keep the bug reports separate We might choose to take up a discussion about your bug report on pgsql hackers if the problem needs more review If you have a problem with the documentation the best place to report it is the documentation mailing list lt pgsql docs postgresql org gt Please be specific about what part of the documentation you are unhappy with If your bug is a portability problem on a non supported platform send mail to lt pgsql ports postgresql org gt so we and you can work on porting PostgreSQL to your platform Note Due to the unfortunate amount of spam going around all of the above email addresses are closed mailing lists That is you need to be subscribed to a list to be allowed to post on it You need not be subscribed to use the bug report web
318. ove backward int count Maximum number of rows to move Outputs None Description SPI cursor move skips over some number of rows in a cursor This is equivalent to the SOL command MOVE 274 SPI cursor close Name SPI cursor close Closes a cursor Synopsis SPI cursor close portal Inputs Portal portal Portal containing cursor Outputs None Description SPI cursor close closes a previously created cursor and releases its Portal storage Usage All open cursors are closed implicitly at transaction end SPI cursor close need only be invoked if it is desirable to release resources sooner 275 SPI saveplan Name SPI saveplan Saves a passed plan Synopsis SPI saveplan plan Inputs void query Passed plan Outputs void Execution plan location NULL if unsuccessful SPI result SPI ERROR ARGUMENT if plan is NULL SPI ERROR UNCONNECTED if procedure is un connected Description SPI saveplan stores a plan prepared by SPI prepare in safe memory protected from freeing by SPI finish or the transaction manager In the current version of PostgreSQL there is no ability to store prepared plans in the system catalog and fetch them from there for execution This will be implemented in future versions As an alternative there is the ability to reuse prepared plans in the subsequent invocations of your procedure in the current session Use SPI execp to execute this saved plan Usa
319. p jdbc postgresql org 77 Chapter 5 JDBC Interface Loading the driver from within the application is covered in Section 5 2 5 1 3 Preparing the Database for JDBC Because Java only uses TCP IP connections the PostgreSQL server must be configured to accept TCP IP connections This can be done by setting tcpip socket true in the postgresql conf file or by supplying the i option flag when starting postmaster Also the client authentication setup in the pg hba cont file may need to be configured Refer to the Administrator s Guide for details The JDBC Driver supports the trust ident password md5 and crypt authentication methods 5 2 Using the Driver 5 2 1 Importing JDBC Any source that uses JDBC needs to import the java sql package using import java sql Important Do not import the org postgresql package If you do your source will not compile as javac Will get confused 5 2 2 Loading the Driver Before you can connect to a database you need to load the driver There are two methods available and it depends on your code which is the best one to use In the first method your code implicitly loads the driver using the C1ass forName method For Post greSQL you would use Class forName org postgresql Driver This will load the driver and while loading the driver will automatically register itself with JDBC Note The forName method can throw a ClassNotFoundException if the driver is not av
320. p1e is not visible to queries in a BEFORE trigger this tuple just inserted is visible to queries in an AFTER trigger and to queries in BEFORE AFTER triggers fired after this 16 4 Examples There are more complex examples in src test regress regress c andin contrib spi Here is a very simple example of trigger usage Function trigf reports the number of tuples in the triggered relation tt est and skips the operation if the query attempts to insert a null value into x i e it acts as a not null constraint but doesn t abort the transaction include executor spi h this is what you need to work with SPI include commands trigger h and triggers extern Datum trigf PG FUNCTION ARGS PG FUNCTION INFO V1 trigf Datum trigf PG FUNCTION ARGS TriggerData trigdata TriggerData fcinfo gt context TupleDesc tupdesc HeapTupl rettuple char when bool checknull false bool isnull int ret i Make sure trigdata is pointing at what I expect if CALLED AS TRIGGER fcinfo elog ERROR trigf not fired by trigger manager tuple to return to Executor if TRIGGER FIRED BY UPDATE trigdata tg event 256 Chapter 16 Triggers rettuple trigdata tg newtuple else rettuple trigdata gt tg_trigtuple check for null values if TRIGGER_FIRED_BY_DELETE trigdata tg event amp amp TRIGGER FIRED BEFORE trigdata tg event check
321. palloc are made in this context When a procedure disconnects from the SPI manager via SPI finish the current context is restored to the upper Executor context and all allocations made in the procedure memory context are freed and can t be used any more All functions described in this section may be used by both connected and unconnected procedures In an unconnected procedure they act the same as the underlying ordinary backend functions palloc etc SPI copytuple Name SPI copytuple Makes copy of tuple in upper Executor context Synopsis SPI copytuple tuple 288 Inputs HeapTuple tuple Input tuple to be copied Outputs HeapTuple Copied tuple non NULL if tuple is not NULL and the copy was successful NULL only if tuple is NULL Description SPI copytuple makes a copy of tuple in upper Executor context Usage TBD SPI copytuple 289 SPI copytupledesc Name SPI copytupledesc Makes copy of tuple descriptor in upper Executor context Synopsis SPI copytupledesc tupdesc Inputs TupleDesc tupdesc Input tuple descriptor to be copied Outputs TupleDesc Copied tuple descriptor non NULL if tupdesc is not NULL and the copy was successful NULL only if tupdesc is NULL Description SPI copytupledesc makes a copy of tupdesc in upper Executor context Usage TBD 290 SPI copytupleintoslot Name SPI copytupleintoslot Makes copy of tuple and descriptor in upper Executor contex
322. pe then the dot notation e g 1 emp may be used to access attributes of the argument 9 2 1 Examples To illustrate a simple SQL function consider the following which might be used to debit a bank account CREATE FUNCTION tpl integer numeric RETURNS integer AS UPDATE bank SET balance balance 2 175 Chapter 9 Extending SQL Functions WHERE accountno 1 SELECT 1 LANGUAGE SQL A user could execute this function to debit account 17 by 100 00 as follows SELECT tpl 17 100 0 In practice one would probably like a more useful result from the function than a constant 1 so a more likely definition is CREATE FUNCTION tpl integer numeric RETURNS numeric AS UPDATE bank SET balance balance 2 WHERE accountno 1 SELECT balance FROM bank WHERE accountno 1 LANGUAGE SQL which adjusts the balance and returns the new balance Any collection of commands in the SQL language can be packaged together and defined as a function The commands can include data modification i e INSERT UPDATE and DELETE as well as SELECT queries However the final command must be a SELECT that returns whatever is specified as the function s return type Alternatively if you want to define a SQL function that performs actions but has no useful value to return you can define it as returning void In tha
323. pe check the fields according to the table definition it just look whether or not it knows how to handle such types 133 putline Name putline write a line to the server socket DA Synopsis putline line Parameters line Line to be written string Return Type none Exceptions TypeError Bad argument type or too many any arguments pg error Invalid connection Description putline method allows to directly write a string to the server socket 134 getline Name get Line get a line from server socket DA Synopsis getline Parameters none Return Type string The line read Exceptions TypeError Bad argument type or too many any arguments pg error Invalid connection Description getline method allows to directly read a string from the server socket 135 endcopy Name endcopy synchronize client and server DA Synopsis endcopy Parameters none Return Type none Exceptions TypeError Bad argument type or too many any arguments pg error Invalid connection Description The use of direct access methods may desynchronize client and server This method ensure that client and server will be synchronized 136 locreate Name locreate create a large object in the database LO Synopsis locreate mode Parameters mode Large object create mode Return Type pglarge Object handling t
324. pe declaration it won t be accepted within PL pgSQL functions Parameters to a function can be composite types complete table rows In that case the corresponding identifier n will be a row variable and fields can be selected from it for example 1 user id Only the user defined attributes of a table row are accessible in a row type variable not OID or other system attributes because the row could be from a view The fields of the row type inherit the table s field size or precision for data types such as char n CREATE FUNCTION use two tables tablename RETURNS TEXT AS DECLARE in t ALIAS FOR 1 312 Chapter 19 PL pgSQL SQL Procedural Language use t table2name ROWTYPE BEGIN SELECT INTO use t FROM table2name WHERE RETURN inm ct fl use ct E3 Ta EES use tti END LANGUAGE plpgsql 19 3 3 Records name RECORD Record variables are similar to row type variables but they have no predefined structure They take on the actual row structure of the row they are assigned during a SELECT or FOR command The substructure of a record variable can change each time it is assigned to A consequence of this is that until a record variable is first assigned to it has no substructure and any attempt to access a field in it will draw a run time error Note that RI ECORD is not a true data type only a placeholder 19
325. pecifies a valid database handle queryString Specifies a valid SQL select query arrayVar Array variable for tuples returned queryProcedure Procedure run on each tuple found Outputs None Description pg select submits a SELECT query to the PostgreSQL backend and executes a given chunk of code for each tuple in the result The gueryString must be a SELECT statement Anything else returns an error The arrayVar variable is an array name used in the loop For each tuple arrayVar is filled in with the tuple field values using the field names as the array indexes Then the queryProcedure is executed In addition to the field values the following special entries are made in the array headers A list of the column names returned by the SELECT numcols The number of columns returned by the SELECT 50 pg select tupno The current tuple number starting at zero and incrementing for each iteration of the loop body Usage This would work if table table has fields cont rol and name and perhaps other fields pg select Spgconn SELECT FROM table array puts format 5d s Sarray control Sarray name 51 pg execute Name pg execute send a query and optionally loop over the results Synopsis pg execute array arrayVar oid oidVar dbHandle queryString queryProcedure Inputs array arrayVar Specifies the name of an array variable where result tuples are store
326. pened first 164 export Name export save the large object to file Synopsis export filename Parameters filename The file to be created Return Type none Exceptions TypeError Bad argument type or too many arguments IOError Object is not closed or export error pg error Invalid connection or invalid object Description export method allows to dump the content of a large object in a very simple way The exported file is created on the host of the program not the server host 165 Il Server Programming This second part of the manual explains the PostgreSQL approach to extensibility and describe how users can extend PostgreSQL by adding user defined types operators aggregates and both query language and programming language functions After a discussion of the PostgreSQL rule system we discuss the trigger and SPI interfaces Chapter 7 Architecture 7 1 PostgreSQL Architectural Concepts Before we begin you should understand the basic PostgreSQL system architecture Understanding how the parts of PostgreSQL interact will make the next chapter somewhat clearer In database jargon Post greSQL uses a simple process per user client server model A PostgreSQL session consists of the fol lowing cooperating Unix processes programs A supervisory daemon process the postmaster the user s frontend application e g the psql program and oneor more backend database server
327. pfree frees memory in upper Executor context Usage This function is no longer different from plain p ree It s kept just for backward compatibility of existing code 296 SPI freetuple Name SPI freetuple Frees a tuple allocated in upper Executor context Synopsis SPI freetuple pointer Inputs HeapTuple pointer Pointer to allocated tuple Outputs None Description SPI freetuple frees a tuple previously allocated in upper Executor context Usage This function is no longer different from plain heap freetuple It s kept just for backward compatibility of existing code 297 SPI freetuptable Name SPI freetuptable Frees a tuple set created by SPI exec or similar function Synopsis SPI freetuptable tuptable Inputs SPITupleTable tuptable Pointer to tuple table Outputs None Description SPI freetuptable frees a tuple set created by a prior SPI query function such as SPI exec Usage This function is useful if a SPI procedure needs to execute multiple queries and does not want to keep the results of earlier queries around until it ends Note that any unfreed tuple sets will be freed anyway at SPI finish 298 SPI freeplan Name SPI freeplan Releases a previously saved plan Synopsis SPI freeplan plan Inputs void plan Passed plan Outputs int SPI ERROR ARGUMENT if plan is NULL Description SPI freeplan releases a query plan previously retu
328. piling it use the LOAD command or begin a fresh session It is recommended to locate shared libraries either relative to 1ibdir or through the dynamic library path This simplifies version upgrades if the new installation is at a different location The actual directory that 1ibdir stands for can be found out with the command pg config pkglibdir Note Before PostgreSQL release 7 2 only exact absolute paths to object files could be specified in CREATE FUNCTION This approach is now deprecated since it makes the function definition unneces sarily unportable It s best to specify just the shared library name with no path nor extension and let the search mechanism provide that information instead 9 5 2 Base Types in C Language Functions Table 9 1 gives the C type required for parameters in the C functions that will be loaded into PostgreSQL The Defined In column gives the header file that needs to be included to get the type definition The actual definition may be in a different file that is included by the listed file It is recommended that users stick to the defined interface Note that you should always include postgres h first in any source file because it declares a number of things that you will need anyway Table 9 1 Equivalent C Types for Built In PostgreSQL Types SQL Type C Type Defined In abstime AbsoluteTime utils nabstime h boolean bool postgres h maybe compi
329. port for access to regular tables is built into PostgreSQL but all index access methods are described in pg am It is possible to add a new index access method by defining the required interface routines and then creating a row in pg am but that is far beyond the scope of this chapter The routines for an index access method do not directly know anything about the data types the access method will operate on Instead an operator class identifies the set of operations that the access method needs to be able to use to work with a particular data type Operator classes are so called because one thing they specify is the set of WHERE clause operators that can be used with an index ie can be converted into an index scan qualification An operator class may also specify some support procedures that are needed by the internal operations of the index access method but do not directly correspond to any WHERE clause operator that can be used with the index It is possible to define multiple operator classes for the same input data type and index access method By doing this multiple sets of indexing semantics can be defined for a single data type For example a B tree index requires a sort ordering to be defined for each data type it works on It might be useful for a complex number data type to have one B tree operator class that sorts the data by complex absolute value another that sorts by real part and so on Typically one of the operator classes
330. pported platforms Here program refers to any executable not only the backend server vi Preface Being slow or resource hogging is not necessarily a bug Read the documentation or ask on one of the mailing lists for help in tuning your applications Failing to comply to the SQL standard is not necessarily a bug either unless compliance for the specific feature is explicitly claimed Before you continue check on the TODO list and in the FAQ to see if your bug is already known If you cannot decode the information on the TODO list report your problem The least we can do is make the TODO list clearer 6 2 What to report The most important thing to remember about bug reporting is to state all the facts and only facts Do not speculate what you think went wrong what it seemed to do or which part of the program has a fault If you are not familiar with the implementation you would probably guess wrong and not help us a bit And even if you are educated explanations are a great supplement to but no substitute for facts If we are going to fix the bug we still have to see it happen for ourselves first Reporting the bare facts is relatively straightforward you can probably copy and paste them from the screen but all too often important details are left out because someone thought it does not matter or the report would be understood anyway The following items should be contained in every bug report The exact sequence of steps f
331. priate I option to your compiler command line 23 Chapter 1 libpq C Library 1 14 Example Programs Example 1 1 libpq Example Program 1 X testlibpq c Test the C version of libpgq the PostgreSQL frontend library include lt stdio h gt include libpq fe h void exit_nicely PGconn conn POfinish conn exit 1 main char pghost pgport pgoptions pgtty char dbName int nFields int a ji FILE debug I PGconn conn PGresult res begin by setting the parameters for a backend connection if the parameters are null then the system will try to use reasonable defaults by looking up environment variables or failing that using hardwired constants y pghost NULL host name of the backend server pgport NULL port of the backend server pgoptions NULL special options to start up the backend server pgtty NULL debugging tty for the backend server dbName templatel make a connection to the database conn PQsetdb pghost pgport pgoptions pgtty dbName 24 Chapter 1 libpq C Library check to see that the backend connection was successfully made if PQstatus conn CONNECTION BAD fprintf stderr Connection to database s failed n dbName fprintf stderr Ss PQerrorMessage conn exit nicely conn debug fopen tmp trace out w
332. procedure it can in fact live to the end of the current transaction Returning the portal name to the procedure s caller provides a way of returning a rowset result Usage If nulls is NULL then SPI cursor open assumes that all parameters if any are NOT NULL 271 SPI cursor find Name SPI cursor find Finds an existing cursor Portal by name Synopsis SPI cursor find name Inputs char name Name of portal Outputs Portal Pointer to Portal with given name or NULL if not found Description SPI cursor find finds a pre existing Portal by name This is primarily useful to resolve a cursor name returned as text by some other function 272 SPI cursor fetch Name SPI cursor fetch Fetches some rows from a cursor Synopsis SPI cursor fetch portal forward count Inputs Portal portal Portal containing cursor bool forward True for fetch forward false for fetch backward int count Maximum number of rows to fetch Outputs SPI tuptable initialized as in SPI exec if successful SPI processed initialized as in SPI exec if successful Description PI_cursor_fetch fetches some more rows from a cursor This is equivalent to the SQL command FETCH n 273 SPI cursor move Name SPI cursor move Moves a cursor Synopsis SPI cursor move portal forward count Inputs Portal portal Portal containing cursor bool forward True for move forward false for m
333. quant hoelace arrive shoelace arrive shoelace ok shoelace ok S Ssl avail After that the rule system runs out of rules and returns the generated parse trees So we end up with two final parse trees that are equal to the SQL statements INSERT INTO shoelace log SELECT Ss sl name S Sl avail shoelace arrive arr quant current user current timestamp FROM shoelace arrive shoelace arrive shoelace data shoelace data shoelace data s WHERE s sl name shoelace arrive arr name AND shoelace data sl name s sl name AND s sl avail shoelace arrive arr quant s sl avail UPDATE shoelace data SET Sl avail shoelace data sl avail shoelace arrive arr quant FROM shoelace arrive shoelace arrive shoelace data shoelace data shoelace data s WHERE s sl name shoelace arrive sl name AND shoelace data sl name s sl name 235 Chapter 13 The Rule System The result is that data coming from one relation inserted into another changed into updates on a third changed into updating a fourth plus logging that final update in a fifth gets reduced into two queries There is a little detail that s a bit ugly Looking at the two queries turns out that the shoelace data relation appears twice in the range table where it could definitely be reduced to one The planner does not handle it and so the execution plan for the rule systems output of the INSERT will be Nested Loop
334. r you should expect that that function could be called as long as either the PGconn object or PGresult objects made from it exist At creation of a PGresult the PG conn s current notice processor pointer is copied into the PGresult for possible use by routines like POgetvalue 1 10 Environment Variables The following environment variables can be used to select default connection parameter values which will be used by PQconnectdb POsetdbLogin and PQsetdb if no value is directly specified by the 20 Chapter 1 libpq C Library calling code These are useful to avoid hard coding database connection information into simple client applications PGHOST sets the default server name If this begins with a slash it specifies Unix domain communica tion rather than TCP IP communication the value is the name of the directory in which the socket file is stored default tmp PGPORT sets the default TCP port number or Unix domain socket file extension for communicating with the PostgreSQL backend PGDATABASE sets the default PostgreSQL database name PGUSER sets the user name used to connect to the database and for authentication PGPASSWORD sets the password used if the backend demands password authentication This function ality is deprecated for security reasons consider migrating to use the HOME pgpass file PGREALM sets the Kerberos realm to use with PostgreSQL if it is different from the local realm If
335. r PostgreSQL application programmers It is divided into three parts The first part of this book describes the client programming interfaces distributed with PostgreSQL Each of these chapters can be read independently Note that there are many other programming interfaces for client programs that are distributed separately and contain their own documentation Readers of the first part should be familiar with using SQL commands to manipulate and query the database see the Post greSQL User s Guide and of course with the programming language that the interface uses The second part of this book is about extending the server functionality with user defined functions data types triggers etc These are advanced topics which should probably be approached only after all the other user documentation about PostgreSQL has been understood The third part of this book described the available server side programming languages This information is related to the second part and is only useful to readers that have read at least the first few chapters thereof This book covers PostgreSQL 7 3 2 only For information on other versions please read the documentation that accompanies that release 4 Overview of Documentation Resources The PostgreSQL documentation is organized into several books PostgreSQL Tutorial An informal introduction for new users PostgreSQL User s Guide Documents the SQL query language environment including data types and funct
336. r choices of operator names it s sufficient to write MERGES and let the system fill in the details As with COMMUTATOR and NEGATOR the system is able to make dummy operator entries if you happen to define the equality operator before the other ones 213 Chapter 11 Extending SQL Operators There are additional restrictions on operators that you mark merge joinable These restrictions are not currently checked by CREATE OP ERATOR but errors may occur when the operator is used if any are not true A merge joinable equality operator must have a merge joinable commutator itself if the two data types are the same or a related equality operator if they are different If there is a merge joinable operator relating any two data types A and B and another merge joinable operator relating B to any third data type C then A and C must also have a merge joinable operator in other words having a merge joinable operator must be transitive Bizarre results will ensue at runtime if the four comparison operators you name do not sort the data values compatibly Note In PostgreSQL versions before 7 3 the MERGES shorthand was not available to make a merge joinable operator one had to write both sonr1 and sort2 explicitly Also the Ltcmp and Grcmp options did not exist the names of those operators were hardwired as and gt respectively 214 Chapter 12 Extending SQL Aggregates Aggregate funct
337. r processing the options array free it by passing it to PQconninfoF ree If this is not done a small amount of memory is leaked for each call to POconndefaults In PostgreSQL versions before 7 0 PQconndefaults returned a pointer to a static array rather than a dynamically allocated array That was not thread safe so the behavior has been changed PQfinish Close the connection to the backend Also frees memory used by the PGconn object void PQfinish PGconn conn Chapter 1 libpq C Library Note that even if the backend connection attempt fails as indicated by PQstatus the application should call POfinish to free the memory used by the PGconn object The PGconn pointer should not be used after POfinish has been called PQreset Reset the communication port with the backend void PQreset PGconn conn This function will close the connection to the backend and attempt to reestablish a new connection to the same server using all the same parameters previously used This may be useful for error recovery if a working connection is lost PQresetStart POresetPoll Reset the communication port with the backend in a nonblocking man ner int PQresetStart PGconn conn PostgresPollingStatusType POQresetPoll PGconn conn These functions will close the connection to the backend and attempt to reestablish a new connection to the same server using all the same parameters previously used This may be useful for error recovery if
338. r some examples 4 6 Error Handling The embedded SQL interface provides a simplistic and a complex way to handle exceptional conditions in a program The first method causes a message to printed automatically when a certain condition occurs For example EXEC SOL WHENEVER sqlerror sqlprint or EXEC SOL WHENEVER not found sqlprint This error handling remains enabled throughout the entire program Note This is not an exhaustive example of usage for the EXEC SQL WHENEVER statement Further examples of usage may be found in SQL manuals e g The LAN TIMES Guide to SQL by Groff and Weinberg For a more powerful error handling the embedded SQL interface provides a struct and a variable with the name sqica as follows struct sqlca 69 Chapter 4 ECPG Embedded SQL in C char sqlcaid 8 long sqlabc long sqlcode Struct int sqlerrml char sqlerrmc 70 sqlerrm char sqlerrp 8 long sqlerrd 6 0 empty Ky 1 OID of processed tuple if applicable y 2 number of rows processed in an INSERT UPDATE 5 or DELETE statement 3 empty 4 empty 5 empty char sqlwarn 8 0 set to W if at least one other is W a 1 if W at least one character string 4 value was truncated when it was ui E stored into a host variable KY 2 empty EJ 3 empty Fy 4 empty 5 empty 6 empty
339. r us when she must pay for IF NEW salary lt 0 THEN RAISE EXCEPTION cannot have a negative salary NEW empname ND IF ti Remember who changed the payroll when EW last date now EW last user current user RETURN NEW END LANGUAGE plpgsql CREATE TRIGGER emp stamp BEFORE INSERT OR UPDATE ON emp FOR EACH ROW EXECUTE PROCEDURE emp stamp 19 10 Examples Here are only a few functions to demonstrate how easy it is to write PL pgSQL functions For more complex examples the programmer might look at the regression test for PL pgSQL One painful detail in writing functions in PL pgSQL is the handling of single quotes The function s source text in CREATE FUNCTION must be a literal string Single quotes inside of literal strings must be either doubled or quoted with a backslash We are still looking for an elegant alternative In the meantime doubling the single quotes as in the examples below should be used Any solution for this in future versions of PostgreSQL will be forward compatible For a detailed explanation and examples of how to escape single quotes in different situations please see Section 19 11 1 1 Example 19 2 A Simple PL pgSQL Function to Increment an Integer The following two PL pgSQL functions are identical to their counterparts from the C language function discussion This functi
340. r values is automatically declared as an integer variable PL pgSQL variables can have any SQL data type such as INTEGER VARCHAR and CHAR Here are some examples of variable declarations user id INTEGER quantity NUMERIC 5 url VARCHAR myrow tablename ROWTYPE myfield tablename fieldname TYPE arow RECORD The general syntax of a variable declaration is name CONSTANT type NOT NULL DEFAULT expression The DEFAULT clause if given specifies the initial value assigned to the variable when the block is entered If the DEFAULT clause is not given then the variable is initialized to the SQL NULL value The CONSTANT option prevents the variable from being assigned to so that its value remains constant for the duration of the block If NOT NULL is specified an assignment of a NULL value results in a run time error All variables declared as NOT NULL must have a non NULL default value specified The default value is evaluated every time the block is entered So for example assigning now to a variable of type timestamp causes the variable to have the time of the current function call not when the function was precompiled Examples quantity INTEGER DEFAULT 32 url varchar http mysite com user id CONSTANT INTEGER 10 19 3 1 Aliases for Function Parameters name ALIAS FOR n Parameters passed to functions are named with the i
341. red as returning sS ETOF sometype the function s final s ECT query is executed to completion and each row it outputs is returned as an element of the set This feature is normally used by calling the function as a table function In this case each row returned by the function becomes a row of the table seen by the query For example assume that table foo has the same contents as above and we say CREATE FUNCTION getfoo int RETURNS setof foo AS SELECT FROM foo WHERE fooid 1 LANGUAGE SQL SELECT FROM getfoo 1 AS t1 fooid foosubid fooname 1 1 Joe d 2 Ed 2 rows Currently functions returning sets may also be called in the target list of a s EL ECT query For each row that the SELECT generates by itself the function returning set is invoked and an output row is generated for each element of the function s result set Note however that this capability is deprecated and may be removed in future releases The following is an example function returning a set from the target list CREATE FUNCTION listchildren text SELECT name FROM nodes WHERE LANGUAGE SQL SELECT FROM nodes name parent Top Childl Top Child2 Top Child3 Top SubChildl Childl SubChild2 Childl 6 rows SELECT listchildren Top listchildren Childl Ch
342. rg postgresql PGConnection myconn addDataType mytype my class name where myconn is an open Connection to PostgreSQL The handling class must extend org postgresql util PGobject 5 7 1 2 Class org postgresql Fastpath public class Fastpath extends Object java lang Object t org postgresql fastpath Fastpath 86 Chapter 5 JDBC Interface Fastpath is an API that exists within the libpq C interface and allows a client machine to execute a function on the database backend Most client code will not need to use this method but it is provided because the Large Object API uses it To use you need to import the org postgresql fastpath package using the line import org postgresql fastpath Then in your code you need to get a FastPath object Fastpath fp org postgresql PGConnection conn getFastpathAPI This will return an instance associated with the database connection that you can use to issue com mands The casing of Connection to org postgresql PGConnection is required as the getFast pathAPI is an extension method not part of JDBC Once you have a Fastpath instance you can use the fastpath methods to execute a backend function See Also FastpathFastpathArg LargeObject 5 7 1 2 1 Methods public Object fastpath int fnid boolean resulttype FastpathArg args throws SQLException Send a function call to the PostgreSQL backend Parameters fnid Function id resulttype True if the result
343. rge join two distinct data types so long as they are logically compatible For example the int2 versus int4 equality operator is merge joinable We only need sorting operators that will bring both data types into a logically compatible sequence Execution of a merge join requires that the system be able to identify four operators related to the merge join equality operator less than comparison for the left input data type less than comparison for the right input data type less than comparison between the two data types and greater than comparison between the two data types These are actually four distinct operators if the merge joinable operator has two different input data types but when the input types are the same the three less than operators are all the same operator It is possible to specify these operators individually by name as the SORT1 SORT2 LTCMP and GTCMP options respectively The system will fill in the default names lt lt gt respectively if any of these are omitted when MERGES is specified Also MERGES will be assumed to be implied if any of these four operator options appear so it is possible to specify just some of them and let the system fill in the rest The input data types of the four comparison operators can be deduced from the input types of the merge joinable operator so just as with COMMUTATOR only the operator names need be given in these clauses Unless you are using peculia
344. rgument For example suppose that EMP is a table containing employee data and therefore also the name of the composite type of each row of the table Here is a function double salary that computes what your salary would be if it were doubled CREATE FUNCTION double salary EMP RETURNS integer AS SELECT 1 salary 2 AS salary LANGUAGE SQL SELECT name double salary EMP AS dream FROM EMP WHERE EMP cubicle point 2 1 Notice the use of the syntax 1 salary to select one field of the argument row value Also notice how the calling SELECT command uses a table name to denote the entire current row of that table as a composite value It is also possible to build a function that returns a composite type This is an example of a function that returns a single EMP row 177 Chapter 9 Extending SQL Functions CREATE FUNCTION new emp RETURNS EMP AS SELECT text None AS name 1000 AS salary 25 AS age point 2 2 AS cubicle LANGUAGE SQL In this case we have specified each of the attributes with a constant value but any computation or ex pression could have been substituted for these constants Note two important things about defining the function Thetarget list order must be exactly the same as that in which the columns appear in the table associated with the composite type Nami
345. rned by SPI prepare orsaved by SPI saveplan 299 Chapter 17 Server Programming Interface 17 4 Visibility of Data Changes PostgreSQL data changes visibility rule during a query execution data changes made by the query itself via SQL function SPI function triggers are invisible to the query scan For example in query INSERT INTO a SELECT FROM a tuples inserted are invisible for SELECT s scan In effect this duplicates the database table within itself subject to unique index rules of course without recursing Changes made by query Q are visible to queries that are started after query Q no matter whether they are started inside Q during the execution of Q or after Q is done 17 5 Examples This example of SPI usage demonstrates the visibility rule There are more complex examples in src test regress regress c and in contrib spi This is a very simple example of SPI usage The procedure execq accepts an SQL query in its first ar gument and tcount in its second executes the query using SPI exec and returns the number of tuples for which the query executed include executor spi h this is what you need to work with SPI int execq text sql int cnt int execq text sql int cnt char query int ret int proc Convert given TEXT object to a C string query DatumGetCString DirectFunctionCalll textout PointerGetDatum sq1 SPI connect ret SPI exec query c
346. rom a specific list to be imported Presently that list includes array bisect binascii calendar cmath codecs errno marshal math md5 mpz operator pcre pickle random re regex sre sha string StringIO struct time whrandom and zlib 358 Bibliography Selected references and readings for SQL and PostgreSQL Some white papers and technical reports from the original POSTGRES development team are available at the University of California Berkeley Computer Science Department web site SQL Reference Books Judith Bowman Sandra Emerson and Marcy Darnovsky The Practical SQL Handbook Using Structured Query Language Third Edition Addison Wesley ISBN 0 201 44787 8 1996 C J Date and Hugh Darwen A Guide to the SQL Standard A user s guide to the standard database language SQL Fourth Edition Addison Wesley ISBN 0 201 96426 0 1997 C J Date An Introduction to Database Systems Volume 1 Sixth Edition Addison Wesley 1994 Ramez Elmasri and Shamkant Navathe Fundamentals of Database Systems 3rd Edition Addison Wesley ISBN 0 805 31755 4 August 1999 Jim Melton and Alan R Simon Understanding the New SQL A complete guide Morgan Kaufmann ISBN 1 55860 245 3 1993 Jeffrey D Ullman Principles of Database and Knowledge Base Systems Volume 1 Computer Science Press 1988 PostgreSQL Specific Documentation Stefan Simkovics Enhancement of the ANSI SQL Implementation of PostgreSQL Department of Infor
347. rom program start up necessary to reproduce the problem This should be self contained it is not enough to send in a bare select statement without the preceding create table and insert statements if the output should depend on the data in the tables We do not have the time to reverse engineer your database schema and if we are supposed to make up our own data we would probably miss the problem The best format for a test case for query language related problems is a file that can be run through the psql frontend that shows the problem Be sure to not have anything in your psqirc start up file An easy start at this file is to use pg dump to dump out the table declarations and data needed to set the scene then add the problem query You are encouraged to minimize the size of your example but this is not absolutely necessary If the bug is reproducible we will find it either way If your application uses some other client interface such as PHP then please try to isolate the offending queries We will probably not set up a web server to reproduce your problem In any case remember to provide the exact input files do not guess that the problem happens for large files or mid size databases etc since this information is too inexact to be of use The output you got Please do not say that it didn t work or crashed If there is an error message show it even if you do not understand it If the program terminates with an operating
348. ronment eee eroe ABS etin p green 358 xi List of Tables 3 I pgtci Commands dedere ib ete est eee obe etes A 5 1 ConnectionPoolDataSource Implementations eeeseeeseeeeeeeenen entente nennen 108 5 2 ConnectionPoolDataSource Configuration Properties essere 108 5 3 DataSource Implementations 0 0 0 eee cee eeeeeeeceescessecaeceeceseseseaeeseecaecaecsaesaeeseceeseaeeeaseaesaaesaeeaeens 109 5 4 DataSource Configuration Properties eren nennen nennen ennt eene 110 5 5 Additional Pooling DataSource Configuration Properties eee 110 1 PostgreSQL System Catalogs 55 ee tet EE ERU EIE EORR ORE 172 9 1 Equivalent C Types for Built In PostgreSQL Types eseeseseeeeeerennneeneeenene enne 183 14 B tree Strate Ses 4o eei ectetuer et ede deo 243 14 2 H ash Strategies iere eit Gove aoe ee pelt ates ed eRe eR RES 243 14 3 R tree Strategles ise eue rrr dove ait Si etna Pee pee imt sd eee e dile ieee 243 14 4 B tree Support Functions sess nnnm nenne ene ennen rentrer etn nete ennen enne 244 14 5 Hash Support Functions srein rere tir de ed eene eedem 244 14 6 R tree Support Functions seen nerne ooren ee rennen nennen tne enr EE SEA eE nete eren ne nennen 244 14 7 GIST Support PUDCTIONS 3 o Ee e et n Ee ie EIE EE E ER ieget 245 19 1 Single Quotes Escaping Chart esesseseeeeeseeeeeeeenenne ener nennen nennen nere enr eten nennen 334
349. rows SQLException thrown if value is invalid for this type Overrides setValue in class PGobject public boolean equals Object obj Parameters obj Object to compare with Returns true if the two boxes are identical Overrides equals in class PGobject public Object clone This must be overridden to allow the object to be cloned Overrides clone in class PGobject 91 public String getValue Returns the PGbox in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGcircle java lang Object l t org postgresql util PGobject t org postgresql geometric PGcircle public class PGcircle extends PGobject implements Serializable Cloneable This represents PostgreSQL s circle data type and a radius Variables public PGpoint center This is the center point double radius This is the radius Constructors public PGcircle double x double y double r Parameters X coordinate of center y coordinate of center r radius of circle public PGcircle PGpoint c double r Parameters c PGpoint describing the circl Chapter 5 JDBC Interface consisting of a point s center r radius of circle public PGcircle String s throws SQLException 92 public Methods public public public public Chapter 5 JDBC Interface Parameters S definition of the circle in PostgreSQL s syntax Throws SQ
350. rst call set GD plan spi prepare SELECT count AS cnt FROM t1 WHERE num gt 1 AND num lt 2 list int4 int4 Spi execp count 1 GD plan list 1 2 return Scnt LANGUAGE pltcl 348 Chapter 20 PL Tcl Tcl Procedural Language Note that each backslash that Tcl should see must be doubled when we type in the function since the main parser processes backslashes too in CREATE FUNCTION We need backslashes inside the query string given to spi prepare to ensure that the n markers will be passed through to spi prepare as is and not replaced by Tcl variable substitution spi lastoid Returns the OID of the row inserted by the last spi exec d or spi execp d query if that query was a single row INSERT If not you get zero quote string Duplicates all occurrences of single quote and backslash characters in the given string This may be used to safely quote strings that are to be inserted into SQL queries given to spi exec or spi prepare For example think about a query string like SELECT val AS ret where the Tcl variable val actually contains doesn t This would result in the final query string SELECT doesn t AS ret which would cause a parse error during spi exec or spi prepare The submitted query should contain SELECT doesn t AS ret which can be formed in PL Tcl as SELECT quote val AS ret
351. rther modifications Copy right 1997 2000 by D Arcy J M Cain You may either choose to use the old mature interface provided by the pg module or otherwise the newer pgdb interface compliant with the DB API 2 0 specification developed by the Python DB SIG Here we describe only the older pg API As long as PyGreSQL does not contain a description of the DB API you should read about the API at http www python org topics database DatabaseAPI 2 0 html A tutorial like introduction to the DB API can be found at http www2 linuxjournal com lj issues issue49 2605 html 6 1 The pg Module The pg module defines three objects pgobject which handles the connection and all the requests to the database pglargeobject which handles all the accesses to PostgreSQL large objects and pgqueryob ject that handles query results If you want to see a simple example of the use of some of these functions see http www druid net rides where you can find a link at the bottom to the actual Python code for the page 6 1 1 Constants Some constants are defined in the pg module dictionary They are intended to be used as a parameters for methods calls You should refer to the libpq description Chapter 1 for more information about them These constants are INV READ INV WRITE large objects access modes used by pgobject locreate and pglarge open SEEK SE SEEK CUR SEEK END positional flags
352. ry time or we can setup a view for it The view for this is CREATE VIEW shoelace obsolete AS SELECT FROM shoelace WHERE NOT EXISTS SELECT shoename FROM shoe WHERE slcolor sl color Its output is al bundy SELECT FROM shoelace obsolete sl name sl avail sl color sl len sl unit sl len cm 4 4 H 236 Chapter 13 The Rule System sl19 O pink 35 inch 88 9 s110 1000 magenta 40 inch 1017 5 For the 1000 magenta shoelaces we must debit Al before we can throw em away but that s another problem The pink entry we delete To make it a little harder for PostgreSQL we don t delete it directly Instead we create one more view CREATE VIEW shoelace candelete AS SELECT FROM shoelace obsolete WHERE sl avail 0 and do it this way DELETE FROM shoelace WHERE EXISTS SELECT FROM shoelace candelet WHERE sl name shoelace sl name Voil al bundy SELECT FROM shoelace sl name sl avail sl color sl len sl unit sl len cm sll 5 black 80 cm 80 s12 6 black 100 cm 100 s17 6 brown 60 cm 60 sl4 8 black 40 inch 101 6 s13 10 black 35 inch 88 9 s18 21 brown 40 inch 101 6 s110 1000 magenta 40 inch 101 6 s15 4 brown 1 m 100 sl6 20 brown 0 9 m 90 9 rows A DELETE on view with
353. s Chapter 18 Procedural Languages 18 1 Introduction PostgreSQL allows users to add new programming languages to be available for writing functions and procedures These are called procedural languages PL In the case of a function or trigger procedure written in a procedural language the database server has no built in knowledge about how to interpret the function s source text Instead the task is passed to a special handler that knows the details of the language The handler could either do all the work of parsing syntax analysis execution etc itself or it could serve as glue between PostgreSQL and an existing implementation of a programming language The handler itself is a special programming language function compiled into a shared object and loaded on demand Writing a handler for a new procedural language is described in Section 9 8 Several procedural languages are available in the standard PostgreSQL distribution which can serve as examples 18 2 Installing Procedural Languages A procedural language must be installed into each database where it is to be used But procedural languages installed in the templatel database are automatically available in all subsequently created databases So the database administrator can decide which languages are available in which databases and can make some languages available by default if he chooses For the languages supplied with the standard distribution the shell script cr
354. s pg exec dbHandle queryString Inputs dbHandle Specifies a valid database handle queryString Specifies a valid SQL query Outputs resultHandle A Tcl error will be returned if pgtcl was unable to obtain a backend response Otherwise a query result object is created and a handle for it is returned This handle can be passed to pg result to obtain the results of the query Description pg exec submits a query to the PostgreSQL backend and returns a result Query result handles start with the connection handle and add a period and a result number Note that lack of a Tcl error is not proof that the query succeeded An error message returned by the backend will be processed as a query result with failure status not by generating a Tcl error in pg exec 47 pg result Name pg result get information about a query result Synopsis pg result resultHandle resultOption Inputs resultHandle The handle for a query result resultOption Specifies one of several possible options Options status the status of the result 6r ror the error message if the status indicates error otherwise an empty string conn the connection that produced the result oid if the command was an INSERT the OID of the inserted tuple otherwise 0 numTuples the number of tuples returned by the query numAttrs the number of attributes in each tuple assign arrayName assign the results to an array using subscripts
355. s as in Example 19 6 One thing to keep in mind when escaping lots of single quotes is that except for the beginning ending quotes all the others will come in even quantity Table 19 1 gives the scoop You ll love this little chart Table 19 1 Single Quotes Escaping Chart quotes in your resulting string and terminate that string nm bar No of Quotes Usage Example Result 1 To begin terminate CREATE FUNC as is function bodies TION foo RE TURNS INTE GER AS LAN GUAGE plpgsql1 2 In assignments SELECT a output Bl amp 4BETZjECT FRO statements to delimit SE users WHERE strings etc LECT FROM users WHEREanfesfafesvaidgbar 4 When you need two a output a ouMNiumale LISND name single quotes in your bar AND foobar AND resulting string without terminating that string 6 When you want double a output a ouANDtn me LAKE name foobar 334 LIKE LIKE Chapter 19 PL pgSQL SQL Procedural Language function to generate other functions like in Example 19 6 No of Quotes Usage Example Result 10 When you want two a output a output 7 ifike re single quotes in the fer Ecco then resulting string which rer_keys kind ld teurti e gt re accounts for 8 quotes fer end if and terminate that string rer keys key string
356. s For example if an R tree index stores only bounding boxes for objects then it cannot exactly satisfy a WHERE condition that tests overlap between nonrectan gular objects such as polygons Yet we could use the index to find objects whose bounding box overlaps the bounding box of the target object and then do the exact overlap test only on the objects found by the index If this scenario applies the index is said to be lossy for the operator and we add RECHECK to the OPERATOR clause in the CREATE OPERATOR CLASS command RECHECK is valid if the index is guaranteed to return all the required tuples plus perhaps some additional tuples which can be eliminated by performing the original operator comparison Consider again the situation where we are storing in the index only the bounding box of a complex object such as a polygon In this case there s not much value in storing the whole polygon in the index entry we may as well store just a simpler object of type box This situation is expressed by the STORAGE option in CREATE OPERATOR CLASS we d write something like CREATE OPERATOR CLASS polygon ops 247 Chapter 14 Interfacing Extensions To Indexes iw EFAULT FOR TYPE polygon USING gist AS STORAGE box At present only the GiST access method supports a STORAGE type that s different from the column data type The GiST compress and decompress support rout
357. s can be specified separated by OR relation The relation name indicates which table the event applies to ROW STATEMENT The FOR EACH clause determines whether the trigger is fired for each affected row or before or after the entire statement has completed Currently only the ROW case is supported 252 Chapter 16 Triggers procedure The procedure name is the function to be called args The arguments passed to the function in the TriggerData structure This is either empty or a list of one or more simple literal constants which will be passed to the function as strings The purpose of including arguments in the trigger definition is to allow different triggers with similar requirements to call the same function As an example there could be a generalized trigger function that takes as its arguments two field names and puts the current user in one and the current time stamp in the other Properly written this trigger function would be independent of the specific table it is triggering on So the same function could be used for INSERT events on any table with suitable fields to automatically track creation of records in a transaction table for example It could also be used to track last update events if defined as an UPDATE trigger Trigger functions return a HeapTuple to the calling executor The return value is ignored for triggers fired AFTER an operation but it allows BEFORE triggers to Return NULL pointer to skip th
358. s the postgres process itself A single postmaster manages a given collection of databases on a single host Such a collection of databases is called a cluster of databases A frontend application that wishes to access a given database within a cluster makes calls to an interface library e g libpq that is linked into the application The library sends user requests over the network to the postmaster Figure 7 1 a which in turn starts a new backend server process Figure 7 1 b 168 Chapter 7 Architecture Figure 7 1 How a connection is established POSTMA STER a frontend sends request ip postmaster via well known network socket POSTMASTER SBRVER c frontend connected w backend server And multiple connections can be established id frontend connected to multiple backend servers N SBRVER server host 169 Chapter 7 Architecture and connects the frontend process to the new server Figure 7 1 c From that point on the frontend process and the backend server communicate without intervention by the postmaster Hence the post master is always running waiting for connection requests whereas frontend and backend processes come and go The 1ibpq library allows a single frontend to make multiple connections to backend processes However each backend process is a single threaded process that can only execute one query at a time so the communication over any one frontend to backend connectio
359. s discussed in A Unified Framework for Version Modeling Using Production Rules in a Database System as well as On Rules Procedures Caching and Views in Database Systems 13 2 What is a Query Tree To understand how the rule system works it is necessary to know when it is invoked and what its input and results are The rule system is located between the query parser and the planner It takes the output of the parser one query tree and the rewrite rules from the pg rewrite catalog which are query trees too with some extra information and creates zero or many query trees as result So its input and output are always things the parser itself could have produced and thus anything it sees is basically representable as an SQL statement Now what is a query tree It is an internal representation of an SQL statement where the single parts that built it are stored separately These query trees are visible when starting the PostgreSQL backend with de bug level 4 and typing queries into the interactive backend interface The rule actions in the pg rewrite system catalog are also stored as query trees They are not formatted like the debug output but they contain exactly the same information Reading a query tree requires some experience and it was a hard time when I started to work on the rule system I can remember that I was standing at the coffee machine and I saw the cup in a target list water and coffee powder in a range table and all the butt
360. s for the conversion So the computed time stamp is updated on each execution as the programmer expects The mutable nature of record variables presents a problem in this connection When fields of a record variable are used in expressions or statements the data types of the fields must not change between calls of one and the same expression since the expression will be planned using the data type that is present when the expression is first reached Keep this in mind when writing trigger procedures that handle events for more than one table EXECUTE can be used to get around this problem when necessary 19 5 Basic Statements In this section and the following ones we describe all the statement types that are explicitly understood by PL pgSQL Anything not recognized as one of these statement types is presumed to be an SQL query and is sent to the main database engine to execute after substitution for any PL pgSQL variables used in 315 Chapter 19 PL pgSQL SQL Procedural Language the statement Thus for example SQL INSERT UPDATE and DELETE commands may be considered to be statements of PL pgSQL But they are not specifically listed here 19 5 1 Assignment An assignment of a value to a variable or row record field is written as identifier expression As explained above the expression in such a statement is evaluated by means of an SQL SELECT com mand sent to the main database engin
361. s some side effects on the interpretation of constant values In detail there is a difference between what these two functions do CREATE FUNCTION logfuncl TEXT RETURNS TIMESTAMP AS DECLARE logtxt ALIAS FOR 1 BEGIN INSERT INTO logtable VALUES logtxt now RETURN now ti D LANGUAGE plpgsql and CREATE FUNCTION logfunc2 TEXT RETURNS TIMESTAMP AS DECLARE logtxt ALIAS FOR 1 curtime timestamp BEGIN curtime now INSERT INTO logtable VALU RETURN curtime Lu S logtxt curtime END LANGUAGE plpgsql In the case of 1og unc1 the PostgreSQL main parser knows when preparing the plan for the INSERT that the string now should be interpreted as timestamp because the target field of logt able is of that type Thus it will make a constant from it at this time and this constant value is then used in all invocations of logfuncl during the lifetime of the backend Needless to say that this isn t what the programmer wanted In the case of 1og unc2 the PostgreSQL main parser does not know what type now should become and therefore it returns a data value of type text containing the string now During the ensuing assign ment to the local variable curtime the PL pgSQL interpreter casts this string to the timestamp type by calling the text out and timestamp in function
362. scaped version of the rom string to the to buffer replacing special characters so that they cannot cause any harm and adding a terminating zero byte The single quotes that must surround PostgreSQL string literals are not part of the result string PQescapeSt ring returns the number of characters written to t o not including the terminating zero byte Behavior is undefined when the to and from strings overlap Chapter 1 libpq C Library 1 3 3 Escaping binary strings for inclusion in SQL queries PQescapeBytea Escapes a binary string bytea type for use within an SQL query unsigned char PQescapeBytea unsigned char from size t from length size t to length Certain ASCII characters must be escaped but all characters may be escaped when used as part of a bytea string literal in an SQL statement In general to escape a character it is converted into the three digit octal number equal to the decimal ASCII value and preceded by two backslashes The single quote C and backslash V characters have special alternate escape sequences See the User s Guide for more information PQescapeBytea performs this operation escaping only the minimally required characters The from parameter points to the first character of the string that is to be escaped and the rom length parameter reflects the number of characters in this binary string a terminating zero byte is neither neces sary nor counted The to length parameter shall point to
363. should try to make the input and output functions inverses of each other If you do not you will have severe problems when you need to dump your data into a file and then read it back in say into someone else s database on another computer This is a particularly common problem when floating point numbers are involved To define the complex type we need to create the two user defined functions complex in and com plex out before creating the type CREATE FUNCTION complex in cstring RETURNS complex AS PGROOT tutorial complex LANGUAGE C CREATE FUNCTION complex out complex RETURNS cstring AS PGROOT tutorial complex LANGUAGE C Finally we can declare the data type CREATE TYPE complex internallength 16 input complex in output complex out Notice that the declarations of the input and output functions must reference the not yet defined type This is allowed but will draw warning messages that may be ignored As discussed earlier PostgreSQL fully supports arrays of base types Additionally PostgreSQL supports arrays of user defined types as well When you define a type PostgreSQL automatically provides support for arrays of that type For historical reasons the array type has the same name as the user defined type with the underscore character _ prepended Composite types do not need any function defined on them since the system already understands what
364. sql org 6 http www postgresql org users lounge Preface In a command synopsis brackets and indicate an optional phrase or keyword Anything in braces and and containing vertical bars indicates that you must choose one alternative Examples will show commands executed from various accounts and programs Commands executed from a Unix shell may be preceded with a dollar sign Commands executed from particular user accounts such as root or postgres are specially flagged and explained SQL commands may be preceded with gt or will have no leading prompt depending on the context Note The notation for flagging commands is not universally consistent throughout the documentation Set Please report problems to the documentation mailing list lt pgsql docs postgresql org gt 6 Bug Reporting Guidelines When you find a bug in PostgreSQL we want to hear about it Your bug reports play an important part in making PostgreSQL more reliable because even the utmost care cannot guarantee that every part of PostgreSQL will work on every platform under every circumstance The following suggestions are intended to assist you in forming bug reports that can be handled in an effective fashion No one is required to follow them but it tends to be to everyone s advantage We cannot promise to fix every bug right away If the bug is obvious critical or affects a lot of users chances are good that someone will look into it
365. ssful a handle for a database connection is returned Handles start with the prefix pgsql Description pg connect opens a connection to the PostgreSQL backend Two syntaxes are available In the older one each possible option has a separate option switch in the pg connect statement In the newer form a single option string is supplied that can contain multiple option values See pg_conndefaults for info about the available options in the newer syntax Usage 44 pg disconnect Name pg disconnect close a connection to the backend server Synopsis pg disconnect dbHandle Inputs dbHandle Specifies a valid database handle Outputs None Description pg disconnect closes a connection to the PostgreSQL backend 45 pg conndefaults Name pg conndefaults obtain information about default connection parameters Synopsis pg conndefaults Inputs None Outputs option list The result is a list describing the possible connection options and their current default values Each entry in the list is a sublist of the format optname label dispchar dispsize value where the optname is usable as an option in pg connect conninfo Description pg conndefaults returns info about the connection options available in pg connect conninfo and the current default value for each option Usage pg conndefaults 46 pg exec Name pg exec send a command string to the server Synopsi
366. ssociated with the object error the last warning error message of the connection Important In multithreaded environments error may be modified by another thread using the same pgob ject Remember that these object are shared not duplicated you should provide some locking if you want to check for the error message in this situation The OID attribute is very interesting because it allow you to reuse the OID later creating the pglarge object with a pgobject get1o method call See also Chapter 2 for more information about the PostgreSQL large object interface Name open open a large object Synopsis open mode 156 Parameters mode open mode definition integer Return Type none Exceptions TypeError Bad parameter type or too many arguments IOError Already opened object or open error pg error Invalid connection Description open open method opens a large object for reading writing in the same way than the Unix open func tion The mode value can be obtained by OR ing the constants defined in the pg module INV_READ INV WRITE 157 close Name close close the large object Synopsis close Parameters none Return Type none Exceptions SyntaxError Too many arguments IOError Object is not opened or close error pg error Invalid connection Description close method closes previously opened large object in the s
367. st specification Exceptions TypeError Bad argument type or too many arguments Description set defhost sets the default host value for new connections If None is supplied as parameter envi ronment variables will be used in future connections It returns the previous setting for default host 118 get defport Name get defport get default port DV Synopsis get defport Parameters none Return Type integer or None Default port specification Exceptions SyntaxError Too many arguments Description get defport returns the current default port specification or None if the environment variables should be used Environment variables will not be looked up 119 set defport Name set defport set default port DV Synopsis set defport port Parameters port New default host integer 1 Return Type integer or None Previous default port specification Exceptions TypeError Bad argument type or too many arguments Description set defport sets the default port value for new connections If 1 is supplied as parameter environ ment variables will be used in future connections It returns the previous setting for default port 120 get defopt Name get defopt get default options specification DV Synopsis get defopt Parameters none Return Type string or None Default options specification Exceptions Sy
368. statement A call handler can avoid repeated lookups of information about the called function by using the 1info fn extra field This will ini tially be NULL but can be set by the call handler to point at information about the PL function On subsequent calls if 1info fn extra is already non NULL then it can be used and the information lookup step skipped The call handler must be careful that 1info gt fn_extra is made to point at mem ory that will live at least until the end of the current query since an Fmgr Info data structure could be kept that long One way to do this is to allocate the extra data in the memory context specified by 1info fn mcext such data will normally have the same lifespan as the FmgrInfo itself But the handler could also choose to use a longer lived context so that it can cache function definition information across queries When a PL function is invoked as a trigger no explicit arguments are passed but the Funct ionCall InfoData s context field points at a TriggerData node rather than being NULL as it is in a plain function call A language handler should provide mechanisms for PL functions to get at the trigger infor mation This is a template for a PL handler written in C 204 Chapter 9 Extending SQL Functions include postgres h include executor spi h include commands trigger h utils elog h e e e include include fmgr h e e e e include access heapam h include utils s
369. support for returning composite data types or rows starts with the Att InMeta data structure This structure holds arrays of individual attribute information needed to create a row from raw C strings It also saves a pointer to the TupleDesc The information carried here is derived from the TupleDesc but it is stored here to avoid redundant CPU cycles on each call to a table function In the case of a function returning a set the Att InMetadata structure should be computed once during the first call and saved for re use in later calls typedef struct AttInMetadata full TupleDesc TupleDesc tupdesc array of attribute type input function finfo FmgrInfo attinfuncs array of attribute type typelem Oid attelems array of attribute typmod int32 atttypmods AttInMetadata 192 Chapter 9 Extending SQL Functions To assist you in populating this structure several functions and a macro are available Use TupleDesc RelationNameGetTupleDesc const char relname to get a TupleDesc based on a specified relation or TupleDesc TypeGetTupleDesc Oid typeoid List colaliases to get a TupleDesc based on a type OID This can be used to get a TupleDesc for a base scalar or composite relation type Then AttInMetadata TupleDescGetAttInMetadata TupleDesc tupdesc will return a pointer to an Att InMetadata initialized based on the given TupleDesc Att InMetadata can be used in conjunction with
370. t Synopsis SPI copytupleintoslot tuple tupdesc Inputs HeapTuple tuple Input tuple to be copied TupleDesc tupdesc Input tuple descriptor to be copied Outputs TupleTableSlot Tuple slot containing copied tuple and descriptor non NULL if tuple and tupdesc are not NULL and the copy was successful NULL only if tuple or tupdesc is NULL Description SPI copytupleintoslot makes a copy of tuple in upper Executor context returning it in the form of a filled in TupleTableSlot Usage TBD 291 SPI modifytuple Name SPI modifytuple Creates a tuple by replacing selected fields of a given tuple Synopsis SPI modifytuple rel tuple nattrs attnum Values Nulls Inputs Relation rel Used only as source of tuple descriptor for tuple Passing a relation rather than a tuple descriptor is a misfeature HeapTuple tuple Input tuple to be modified int nattrs Number of attribute numbers in attnum array int attnum Array of numbers of the attributes that are to be changed Datum Values New values for the attributes specified char Nulls Which new values are NULL if any Outputs HeapTuple New tuple with modifications non NULL if tuple is not NULL and the modify was successful NULL only if tuple is NULL SPI result SPI ERROR ARGUMENT if rel is NULL or tuple is NULL or natts lt 0 or attnum is NULL or Values is NULL SPI ERROR NOATTRIBUTE if there is an invalid attribute number in attnum att
371. t case it must not end with a SELECT For example CREATE FUNCTION clean EMP RETURNS void AS DELETE FROM EMP WHERE EMP salary lt 0 LANGUAGE SQL SELECT clean EMP clean emp 9 2 2 SQL Functions on Base Types The simplest possible SQL function has no arguments and simply returns a base type such as integer CREATE FUNCTION one RETURNS integer AS SELECT 1 as RESULT LANGUAGE SQL SELECT one one 176 Chapter 9 Extending SQL Functions Notice that we defined a column alias within the function body for the result of the function with the name RESULT but this column alias is not visible outside the function Hence the result is labeled one instead of RESULT It is almost as easy to define SQL functions that take base types as arguments In the example below notice how we refer to the arguments within the function as 1 and 2 CREATE FUNCTION add em integer integer RETURNS integer AS SELECT 1 2 LANGUAGE SQL SELECT add em 1 2 AS answer answer 9 2 3 SQL Functions on Composite Types When specifying functions with arguments of composite types we must not only specify which argument we want as we did above with 1 and 2 but also the attributes of that a
372. t from pg lo open buf Specifies a valid string variable to write to the large object len Specifies the maximum size of the string to write Outputs None Description pg lo write writes at most len bytes to a large object from a variable buf Usage buf must be the actual string to write not a variable name 60 pg lo Iseek Name pg lo lseek seek to a position in a large object Synopsis pg lo lseek conn fd offset whence Inputs conn Specifies a valid database connection fd File descriptor for the large object from pg lo open offset Specifies a zero based offset in bytes whence whence can be SEEK CUR SEEK END or SEEK SET Outputs None Description pg 1o lseek positions to offset bytes from the beginning of the large object Usage whence can be SEEK CUR SEEK END Or SEEK SET 61 pg lo tell Name pg lo tell return the current seek position of a large object Synopsis pg lo tell conn fd Inputs conn Specifies a valid database connection fd File descriptor for the large object from pg lo open Outputs offset A zero based offset in bytes suitable for input to pg 1o lseek Description pg 1o tell returns the current to of fset in bytes from the beginning of the large object Usage 62 pg lo unlink Name pg lo unlink delete a large object Synopsis pg
373. t point p2 second point public PGline String s throws SQLException Parameters S definition of the line in PostgreSQL s syntax Throws SQLException on conversion failure public PGline required by the driver Methods public void setValue String s throws SQLException 94 Chapter 5 JDBC Interface Parameters S Definition of the line segment in PostgreSQL s syntax Throws SQLException on conversion failure Overrides setValue in class PGobject public boolean equals Object obj Parameters obj Object to compare with Returns true if the two lines are identical Overrides equals in class PGobject public Object clone This must be overridden to allow the object to be cloned Overrides clone in class PGobject public String getValue Returns the PGline in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGlseg java lang Object l t org postgresql util PGobject t org postgresql geometric PGlseg public class PGlseg extends PGobject implements Serializable Cloneable This implements a lseg line segment consisting of two points Variables public PGpoint point 95 Chapter 5 JDBC Interface These are the two points Constructors public PGlseg double double double double Parameters xl yl AX oe y2 x1 yl x2 y2 coordinate coordinate coord
374. t result EX EC SOL DECLARE n EC EX EC SOL H ECT res INTO Is translated into Processed by ecpg 2 These two include fil include lt ecpgtype h gt include lt ecpglib h gt TION result FROM mytable WH 6 0 exec sql begin declar line 1 int index int result ER E index index S are added by the preprocessor section foo pgc 75 Chapter 4 ECPG Embedded SQL in C exec sql end declare section ECPGdo LINE NULL SELECT res FROM mytable WHERE index ECPGt int amp index 1L 1L sizeof int ECPGt NO INDICATOR NULL OL OL OL ECPGt EOIT ECPGt_int amp result 1L 1L sizeof int ECPGt_NO_INDICATOR NULL OL OL OL ECPGt_EORT line 147 foo pgc The indentation in this manual is added for readability and not something the preprocessor does 4 11 2 The Library The most important function in the library is ECPGdo It takes a variable number of arguments Hopefully there are no computers that limit the number of variables that can be accepted by a varargs function This can easily add up to 50 or so arguments The arguments are A line number This is a line number of the original line used in error messages only A string This is the SQL query that is to be issued It is modif
375. t ttr PEPPER TRE RR E 310 19 5 Declaration eerte eee DEL EUR EE ERR UE ER IEEE HER AE TEAS 310 19 3 1 Aliases for Function Parameters essere ener nennen 311 19 3 2 ROW Types see eec rete e ie nce REP I Here 312 19 3 3 RECOS oc Rt RIPE PEDE ERR bee ITUE 313 19 3 4 Attributes cities neh ee eo UR ede DUE Gn E 313 19 3 5 RENAME eee eee eene ee IP eene 314 19 4 ExpressIOnS ise ane aha Fed ee Eel i rete ctr ICE de ete uds 314 19 5 Basic Statements sce rd Wr PRA seh RR ERU ERE UE RETE 315 19 5 1 ASSIeDT EnE ie eei dep teet ice Saas 316 19 5 2 SELECT INTO cte teenti nem edes gue 316 19 5 3 Executing an expression or query with no result sees 317 19 5 4 Executing dynamic queries eene nennen 317 19 55 Obtains result status eerte een tee dele tete eges 319 19 6 Control Str ctures e tee epe sched RC rei E teaser te apte nes 320 19 6 1 Returning from a function eene ener 320 19 6 2 Conditionals eR Ga ee Ae Eee 321 19 6 2 T XE THEN tee hte Ree eie e t eds 321 19 6 2 2 IF THENSELSE ha ithe a ahd ote i oe Ok 321 19 6 2 3 TRATHEN BUSEY TRA sites bed eene sette Retire esos 322 19 6 2 4 IF THEN ELSIE ELSE v aee 322 19 6 3 Simple LOOPS ioi tent a ER AER ASEE S E SEER SEE 323 19 6 3 T LOOP zi nerve eme RIS 323 1963 2 EXT iioii eee ERE e eere bte E cm 323 19 6 3 3 WHILE isch ase etn ei PRU ut 324 19 6 3 4 FOR integer for loop seesteinen ee eieo e 324 19 6 4 Lo
376. te Usage Attribute numbers are 1 based 281 SPI getvalue Algorithm The result is returned as a palloc d string Use pfree to release the string when done with it 282 SPI getbinval Name SPI getbinval Returns the binary value of the specified attribute Synopsis SPI getbinval tuple tupdesc fnumber isnull Inputs HeapTuple tuple Input tuple to be examined TupleDesc tupdesc Input tuple description int fnumber Attribute number Outputs Datum Attribute binary value bool isnull flag for null value in attribute SPI result SPI ERROR NOATTRIBUTE Description SPI getbinval returns the specified attribute s value in internal form as a Datum 283 SPI getbinval Usage Attribute numbers are 1 based Algorithm Does not allocate new space for the datum In the case of a pass by reference data type the Datum will be a pointer into the given tuple 284 SPI gettype Name SPI gettype Returns the type name of the specified attribute Synopsis SPI gettype tupdesc fnumber Inputs TupleDesc tupdesc Input tuple description int fnumber Attribute number Outputs char The type name for the specified attribute number SPI result SPI ERROR NOATTRIBUTE Description SPI gettype returns a copy of the type name for the specified attribute or NULL on error Usage Attribute numbers are 1 based Algorithm Returns a newly allocated copy of the
377. te 2 lseek 2 etc User functions call these routines to retrieve only the data of interest from a large object For example if a large object type called mugshot existed that stored photographs of faces then a function called beard could be declared on mugshot data beard could look at the lower third of a photograph and determine the color of the beard that appeared there if any The entire large object value need not be buffered or even examined by the beard function Large objects may be accessed from dynamically loaded C functions or database client programs that link the library PostgreSQL provides a set of routines that support opening reading writing closing and seeking on large objects 2 3 1 Creating a Large Object The routine Oid lo creat PGconn conn int mode creates a new large object mode is a bit mask describing several different attributes of the new object The symbolic constants listed here are defined in the header file 11bpg 1ibpq fs h The access type read write or both is controlled by or ing together the bits INv READ and INV WRITE The low order sixteen bits of the mask have historically been used at Berkeley to designate the storage manager number on which the large object should reside These bits should always be zero now The commands below create a large object inv oid lo creat INV READ INV WRITE 2 3 2 Importing a Large Object To import an operating system file as a lar
378. te The cursor cannot be open already and it must have been declared as an unbound cursor that is as a simple refcursor variable The SELECT query is treated in the same way as other SELECT statements in PL pgSQL PL pgSQL variable names are substituted and the query plan is cached for possible re use OPEN cursl FOR SELECT FROM foo WHERE key mykey 19 7 2 2 OPEN FOR EXECUTE OPEN unbound cursor FOR EXECUTE query string The cursor variable is opened and given the specified query to execute The cursor cannot be open already and it must have been declared as an unbound cursor that is as a simple refcursor variable The query is specified as a string expression in the same way as in the EXECUTE command As usual this gives flexibility so the query can vary from one run to the next OPEN cursl FOR EXECUTE SELECT FROM quote ident 1 19 7 2 3 Opening a bound cursor OPEN bound cursor argument values This form of OPEN is used to open a cursor variable whose query was bound to it when it was declared The cursor cannot be open already A list of actual argument value expressions must appear if and only if the cursor was declared to take arguments These values will be substituted in the query The query plan for a bound cursor is always considered cacheable there is no equivalent of EXECUTE in this case OPEN curs2 OPEN curs3 42
379. ted with the given field index Field indices start at 0 char PQfname const PGresult res int field index PQfnumber Returns the field column index associated with the given field name int PQfnumber const PGresult res 10 Chapter 1 libpq C Library const char field name is returned if the given name does not match any field POftype Returns the field type associated with the given field index The integer returned is an internal coding of the type Field indices start at 0 Oid POftype const PGresult res int field index You can query the system table pg type to obtain the name and properties of the various data types The OIDs of the built in data types are defined in src include catalog pg_type h in the source tree POfmod Returns the type specific modification data of the field associated with the given field index Field indices start at 0 int PQfmod const PGresult res int field index POfsize Returns the size in bytes of the field associated with the given field index Field indices start at 0 int PQfsize const PGresult res int field index POfsize returns the space allocated for this field in a database tuple in other words the size of the server s binary representation of the data type 1 is returned if the field is variable size PQbinaryTuples Returns 1 if the PGresult contains binary tuple data 0 if it contains ASCII data int PObinaryTuples const PGresult res
380. than 5 Hash indexes express only bitwise similarity and so they define only 1 strategy as shown in Table 14 2 Table 14 2 Hash Strategies Operation Strategy Number equal 1 R tree indexes express rectangle containment relationships They define 8 strategies as shown in Table 14 3 Table 14 3 R tree Strategies Operation Strategy Number left of left of or overlapping 2 overlapping 3 right of or overlapping 4 right of 5 same 6 contains 7 8 contained by GiST indexes are even more flexible they do not have a fixed set of strategies at all Instead the con sistency support routine of a particular GiST operator class interprets the strategy numbers however it 243 Chapter 14 Interfacing Extensions To Indexes likes By the way the amorderstrategy column in pg am tells whether the access method supports ordered scan Zero means it doesn t if it does amorderstrategy is the strategy number that corresponds to the ordering operator For example B tree has amorderstrategy l which is its less than strategy number In short an operator class must specify a set of operators that express each of these semantic ideas for the operator class s data type 14 4 Access Method Support Routines Strategies aren t usually enough information for the system to figure out how to use an index In practice the access methods require additional support rou
381. the query result columns Except for the INTO clause the SELECT statement is the same as a normal SQL SELECT query and can use the full power of SELECT If the SELECT query returns zero rows null values are assigned to the target s If the SELECT query returns multiple rows the first row is assigned to the target s and the rest are discarded Note that the first row is not well defined unless you ve used ORDER BY At present the INTO clause can appear almost anywhere in the SELECT query but it is recommended to place it immediately after the SELECT keyword as depicted above Future versions of PL pgSQL may be less forgiving about placement of the INTO clause 316 Chapter 19 PL pgSQL SQL Procedural Language You can use FOUND immediately after a SELECT INTO statement to determine whether the assignment was successful that is at least one row was was returned by the SELECT statement For example SELECT INTO myrec FROM EMP WHERE empname myname IF OT FOUND THEN RAISE EXCEPTION employee not found myname END IF Alternatively you can use the I8 NULL or ISNULL conditional to test for whether a RECORD ROW result is null Note that there is no way to tell whether any additional rows might have been discarded DECLARE users rec RECORD full name varchar BEGIN SE H ECT INTO users rec FROM users WHERE user
382. thing else is absolutely the same So having two tables t1 and t2 with attributes a and b the parse trees for the two statements SELECT t2 b FROM tl t2 WHERE tl a t2 a UPDATE t1 SET b t2 b WHERE tl a t2 a are nearly identical The range tables contain entries for the tables t1 and t2 The target lists contain one variable that points to attribute b of the range table entry for table t2 The qualification expressions compare the attributes a of both ranges for equality The join trees show a simple join between t1 and t2 225 Chapter 13 The Rule System The consequence is that both parse trees result in similar execution plans They are both joins over the two tables For the UPDATE the missing columns from t1 are added to the target list by the planner and the final parse tree will read as UPDATE t1 SET a tl a b t2 b WHERE tl a t2 a and thus the executor run over the join will produce exactly the same result set as a SELECT tl a t2 b FROM t1 t2 WHERE tl a t2 a will do But there is a little problem in UPDATE The executor does not care what the results from the join it is doing are meant for It just produces a result set of rows The difference that one is a SELECT command and the other is an UPDATE is handled in the caller of the executor The caller still knows looking at the parse tree that this is an
383. tines in order to work For example the B tree access method must be able to compare two keys and determine whether one is greater than equal to or less than the other Similarly the R tree access method must be able to compute intersections unions and sizes of rectangles These operations do not correspond to operators used in qualifications in SQL queries they are administrative routines used by the access methods internally Just as with operators the operator class identifies which specific functions should play each of these roles for a given data type and semantic interpretation The index access method specifies the set of functions it needs and the operator class identifies the correct functions to use by assigning support function numbers to them B trees require a single support function as shown in Table 14 4 Table 14 4 B tree Support Functions Function Support Number Compare two keys and return an integer less than l Zero Zero or greater than zero indicating whether the first key is less than equal to or greater than the second Hash indexes likewise require one support function as shown in Table 14 5 Table 14 5 Hash Support Functions Function Support Number Compute the hash value for a key 1 R tree indexes require three support functions as shown in Table 14 6 Table 14 6 R tree Support Functions Function Support Number lunion 1 intersection 2
384. tion which is often not thread safe It is better to use MD5 encryption which is thread safe on all platforms 1 13 Building Libpq Programs To build i e compile and link your libpq programs you need to do all of the following things Include the 1ibpq fe h header file include libpq fe h If you failed to do that then you will normally get error messages from your compiler similar to foo c In function main foo c 34 PGconn undeclared first use in this function foo c 35 PGresult undeclared first use in this function foo c 54 CONNECTION BAD undeclared first use in this function foo c 68 PGRES COMMAND OK undeclared first use in this function foo c 95 PGRES TUPLES OK undeclared first use in this function Point your compiler to the directory where the PostgreSQL header files were installed by supplying the Idirectory option to your compiler In some cases the compiler will look into the directory in question by default so you can omit this option For instance your compile command line could look like cc c I usr local pgsqal include testprog c 22 Chapter 1 libpq C Library If you are using makefiles then add the option to the CPPFLAGS variable CPPFLAGS I usr local pgsql include If there is any chance that your program might be compiled by other users then you should not hardcode the directory location like that Instead you can run the utility pg_config
385. tion will be the last in this document but not the last example First there was the parser s output INSERT INTO shoelace ok SELECT shoelace arrive arr name shoelace arrive arr quant FROM shoelace arrive shoelace arrive shoelace ok shoelace ok Now the first rule shoelace ok ins is applied and turns it into UPDATE shoelace SET Sl avail int4pl shoelace sl avail shoelace arrive arr quant FROM shoelace arrive shoelace arrive shoelace ok shoelace ok shoelace ok OLD shoelace ok NEW shoelace shoelac WHERE bpchareq shoelace sl name showlace arrive arr name and throws away the original INSERT on shoelace ok This rewritten query is passed to the rule system again and the second applied rule shoelace_upd produced UPDATE shoelace data SET sl name shoelace sl name Sl avail int4pl shoelace sl avail shoelace arrive arr quant sl color shoelace sl color sl len shoelace sl len sl unit shoelace sl unit FROM shoelace arrive shoelace arrive shoelace ok shoelace ok shoelace ok OLD shoelace ok NEW shoelace shoelace shoelace OLD shoelace NEW shoelace data showlace data WHERE bpchareq shoelace sl name showlace arrive arr name AND bpchareq shoelace data sl name shoelace sl name Again it s an INSTEAD rule and the previous parse tree is trashed Note that this query still uses the view shoelace But the rule syste
386. tiversion concurrency control supporting almost all SQL constructs including subselects transactions and user defined types and functions and having a wide range of language bind ings available including C C Java Perl Tcl and Python 2 1 The Berkeley POSTGRES Project Implementation of the POSTGRES DBMS began in 1986 The initial concepts for the system were pre sented in The design of POSTGRES and the definition of the initial data model appeared in The POST GRES data model The design of the rule system at that time was described in The design of the POST GRES rules system The rationale and architecture of the storage manager were detailed in The design of the POSTGRES storage system Postgres has undergone several major releases since then The first demoware system became opera tional in 1987 and was shown at the 1988 ACM SIGMOD Conference Version 1 described in The im plementation of POSTGRES was released to a few external users in June 1989 In response to a critique of the first rule system A commentary on the POSTGRES rules system the rule system was redesigned On Rules Procedures Caching and Views in Database Systems and Version 2 was released in June 1990 with the new rule system Version 3 appeared in 1991 and added support for multiple storage managers an improved query executor and a rewritten rewrite rule system For the most part subsequent releases until Postgres95 see below focused on portabilit
387. to Concatenate Text sess 333 19 4 A PL pgSQL Function on Composite Type eese nennen enne 333 19 5 A Simple E nctiomr o ee eet er ERREUR ETE E EYE ERREUR EIER EU TENEO RYE URS 335 19 6 A Function that Creates Another Function eesessseseeeeee neret nennen ener 336 xii 19 7 A Procedure with a lot of String Manipulation and OUT Parameters sese 337 xiii Preface 1 What is PostgreSQL PostgreSQL is an object relational database management system ORDBMS based on POSTGRES Version 4 2 developed at the University of California at Berkeley Computer Science Department The POSTGRES project led by Professor Michael Stonebraker was sponsored by the Defense Advanced Research Projects Agency DARPA the Army Research Office ARO the National Science Foundation NSF and ESL Inc PostgreSQL is an open source descendant of this original Berkeley code It provides SQL92 SQL99 lan guage support and other modern features POSTGRES pioneered many of the object relational concepts now becoming available in some commer cial databases Traditional relational database management systems RDBMS support a data model con sisting of a collection of named relations containing attributes of a specific type In current commercial systems possible types include floating point numbers integers character strings money and dates It is commonly recognized that this model is
388. try to cancel the ongoing command It can be done from a signal handler but not otherwise PQexec can return only one PGresult structure If the submitted command string contains multiple SQL commands all but the last PGresult are discarded by PQexec Applications that do not like these limitations can instead use the underlying functions that PQexec is built from POsendQuery and PQgetResult Older programs that used this functionality as well as PQput line and PQputnbytes could block waiting to send data to the backend To address that issue the function PQsetnonblocking was added Old applications can neglect to use PQsetnonblocking and get the older potentially blocking behavior Newer programs can use POsetnonblocking to achieve a completely nonblocking connection to the backend PQsetnonblocking Sets the nonblocking status of the connection int PQsetnonblocking PGconn conn int arg Sets the state of the connection to nonblocking if arg is 1 blocking if arg is 0 Returns 0 if OK 1 if error In the nonblocking state calls to PQput line POputnbytes POsendQuery and PQendcopy will not block but instead return an error if they need to be called again When a database connection has been set to nonblocking mode and PQexec is called it will temporarily set the state of the connection to blocking until the PQexec completes 13 Chapter 1 libpq C Library More of libpq is expected to be made safe for PQsetnonblocking
389. ts out of you On the other hand if your input files are huge it is fair to ask first whether somebody is interested in looking into it Do not spend all your time to figure out which changes in the input make the problem go away This will probably not help solving it If it turns out that the bug cannot be fixed right away you will still have time to find and share your work around Also once again do not waste your time guessing why the bug exists We will find that out soon enough When writing a bug report please choose non confusing terminology The software package in total is called PostgreSQL sometimes Postgres for short If you are specifically talking about the backend server mention that do not just say PostgreSQL crashes A crash of a single backend server process is quite different from crash of the parent postmaster process please don t say the postmaster crashed when you mean a single backend went down nor vice versa Also client programs such as the interactive frontend psql are completely separate from the backend Please try to be specific about whether the problem is on the client or server side 6 3 Where to report bugs In general send bug reports to the bug report mailing list at lt pgsql bugs postgresql org gt You are viii Preface requested to use a descriptive subject for your email message perhaps parts of the error message Another method is to fill in the bug report web f
390. turn from PQconnect Start call status PQstatus conn If status equals CONNECTION BAD PQconnectStart has failed If PQconnectStart succeeds the next stage is to poll libpq so that it may proceed with the con nection sequence Loop thus Consider a connection inactive by default If PoconnectPo11 last returned PGRES POLLING ACTIVE consider it active instead If POconnectPoll conn last re turned PGRES POLLING READING perform a select for reading on POsocket conn If it last returned PGRES POLLING WRITING perform a select for writing on POsocket conn If you have yet to call PQconnectPoll i e after the call to POconnectStart behave as if it last re turned PGRES POLLING WRITING If the select shows that the socket is ready consider it ac tive If it has been decided that this connection is active call PoconnectPoll conn again If this call returns PGRES POLLING FAILED the connection procedure has failed If this call returns PGRES POLLING CK the connection has been successfully made Note that the use of select to ensure that the socket is ready is merely a likely example those with other facilities available such as a po11 call may of course use that instead At any time during connection the status of the connection may be checked by calling PQstatus If this is CONNECTION BAD then the connection procedure has failed if this is CONNECTION OK then
391. turns the Fastpath API for the current connection It is primarily used by the Large Object API The best way to use this is as follows import org postgresql fastpath 85 Chapter 5 JDBC Interface Fastpath fp org postgresql PGConnection myconn getFastpathAPI where myconn is an open Connect ion to PostgreSQL Returns Fastpath object allowing access to functions on the PostgreSQL backend Throws SQLException by Fastpath when initializing for first time public LargeObjectManager getLargeObjectAPI throws SQLException This returns the Large Object API for the current connection The best way to use this is as follows import org postgresql largeobject LargeObjectManager lo org postgresql PGConnection myconn getLargeObjectAPI where myconn is an open Connect ion to PostgreSQL Returns LargeObject object that implements the API Throws SQLException by LargeObject when initializing for first time public void addDataType String type String name This allows client code to add a handler for one of PostgreSQL s more unique data types Normally a data type not known by the driver is returned by ResultSet getObject as a PGobject instance This method allows you to write a class that extends PGob ject and tell the driver the type name and class name to use The down side to this is that you must call this method each time a connection is made The best way to use this is as follows o
392. type name Use pfree to release the copy when done with it 285 SPI gettypeid Name SPI gettypeid Returns the type OID of the specified attribute Synopsis SPI gettypeid tupdesc fnumber Inputs TupleDesc tupdesc Input tuple description int fnumber Attribute number Outputs OID The type OID for the specified attribute number SPI result SPI ERROR NOATTRIBUTE Description SPI gettypeid returns the type OID for the specified attribute Usage Attribute numbers are 1 based 286 SPI getrelname Name SPI getrelname Returns the name of the specified relation Synopsis SPI getrelname rel Inputs Relation rel Input relation Outputs char The name of the specified relation Description SPI getrelname returns the name of the specified relation Algorithm Returns a newly allocated copy of the rel name Use pfree to release the copy when done with it 287 17 3 Memory Management PostgreSQL allocates memory within memory contexts which provide a convenient method of managing allocations made in many different places that need to live for differing amounts of time Destroying a context releases all the memory that was allocated in it Thus it is not necessary to keep track of individual objects to avoid memory leaks only a relatively small number of contexts have to be managed palloc and related functions allocate memory from the current context SPI co
393. ue ResultSet rs st executeQuery while rs next System out print Column 1 returned System out println rs getString 1 rs close st close 80 Chapter 5 JDBC Interface 5 3 1 Using the statement Or PreparedStatement Interface The following must be considered when using the Statement or PreparedStatement interface You can use a single Statement instance as many times as you want You could create one as soon as you open the connection and use it for the connection s lifetime But you have to remember that only one ResultSet can exist per Statement or PreparedStatement at a given time If you need to perform a query while processing a ResultSet you can simply create and use another Statement If you are using threads and several are using the database you must use a separate Statement for each thread Refer to Section 5 8 if you are thinking of using threads as it covers some important points When you are done using the Statement or PreparedStatement you should close it 5 3 2 Using the ResultSet Interface The following must be considered when using the ResultSet interface Before reading any values you must call next This returns true if there is a result but more impor tantly it prepares the row for processing Under the JDBC specification you should access a field only once It is safest to stick to this rule although at the current time the PostgreSQL driver will a
394. uery processing or invalid connection Description query method sends a SQL query to the database If the query is an insert statement the return value is the OID of the newly inserted row If it is otherwise a query that does not return a result i e is not a some kind of SELECT statement it returns None Otherwise it returns a pgqueryobject that can be accessed via the get result or dictresult methods or simply printed 128 reset Name reset reset the connection Synopsis reset Parameters none Return Type none Exceptions TypeError Too many any arguments Description reset method resets the current database 129 close Name close close the database connection Synopsis close Parameters none Return Type none Exceptions TypeError Too many any arguments Description close method closes the database connection The connection will be closed in any case when the connection is deleted but this allows you to explicitly close it It is mainly here to allow the DB SIG API wrapper to implement a close function 130 fileno Name fileno return the socket used to connect to the database Synopsis fileno Parameters none Return Type socket id The underlying socket id used to connect to the database Exceptions TypeError Too many any arguments Description fileno method returns the u
395. ural Language EATE OR R EPLACE PACKAGE BODY acs FUNCTION add_user user_id IN users user id TYPE DEFAULT NULL object type IN acs objects object type TYPE DEFAULT user creation date IN acs objects creation date TYPE DEFAULT sysdate creation user IN acs objects creation user TYPE DEFAULT NULL creation ip IN acs objects creation ip TYPE DEFAULT NULL IE R IS v user id ETURN users user id TYP users user id TYPE v rel id EGIN v user id acs user new user id creation user ETURN v user id END D acs Ow errors membership rels rel id TYPE creation ip object type email creation date We port this to PostgreSQL by creating the different objects of the Oracle package as functions with a standard naming convention We have to pay attention to some other details like the lack of default parameters in PostgreSQL functions The above package would become something like this CR R m EATE FUNCTION acs add user INT EG ER INT EG TURNS INTEGER AS DE CLARE m user id ALIAS FOR 1 object type ALIAS FOR 2 creation date ALIAS FOR 3 creation user ALIAS FOR 4 creation ip ALIAS FOR 5 v user id users user id TYPE v rel id membership rels rel id TYP EGIN v user id
396. urn t if 1 age lt 30 amp amp 100000 0 lt S1 salary return t return f LANGUAGE pltcl There is not currently any support for returning a composite type result value 346 Chapter 20 PL Tcl Tcl Procedural Language 20 2 2 Data Values in PL Tcl The argument values supplied to a PL Tcl function s script are simply the input arguments converted to text form just as if they had been displayed by a SELECT statement Conversely the ret urn command will accept any string that is acceptable input format for the function s declared return type So the PL Tcl programmer can manipulate data values as if they were just text 20 2 3 Global Data in PL Tcl Sometimes it is useful to have some global status data that is held between two calls to a procedure or is shared between different procedures This is easily done since all PL Tcl procedures executed in one backend share the same safe Tcl interpreter So any global Tcl variable is accessible to all PL Tcl proce dure calls and will persist for the duration of the SQL client connection Note that PL TclU functions likewise share global data but they are in a different Tcl interpreter and cannot communicate with PL Tcl functions To help protect PL Tcl procedures from unintentionally interfering with each other a global array is made available to each procedure via the upvar command The global name of this variable is the procedure s int
397. urn Type string or None Previous default debug terminal specification Exceptions TypeError Bad argument type or too many arguments Description set deftty sets the default terminal value for new connections If None is supplied as parameter en vironment variables will be used in future connections It returns the previous setting for default terminal 124 get defbase Name get defbase get default database name specification DV Synopsis get defbase Parameters none Return Type string or None Default debug database name specification Exceptions SyntaxError Too many arguments Description get defbase returns the current default database name specification or None if the environment variables should be used Environment variables will not be looked up 125 set defbase Name set defbase set default database name specification DV Synopsis set defbase database Parameters database New default database name string None Return Type string or None Previous default database name specification Exceptions TypeError Bad argument type or too many arguments Description set defbase sets the default database name for new connections If None is supplied as parame ter environment variables will be used in future connections It returns the previous setting for default database name 126 6 3 Connection Object pgobject This o
398. used by pglarge seek l http www python org topics database DatabaseAPI 2 0 html 113 version version constants that give the current version 6 2 pg Module Functions pg module defines only a few methods that allow to connect to a database and to define default variables that override the environment variables used by PostgreSQL These default variables were designed to allow you to handle general connection parameters without heavy code in your programs You can prompt the user for a value put it in the default variable and forget it without having to modify your environment The support for default variables can be disabled by setting the DNO DEF VAR option in the Python Setup file Methods relative to this are specified by the tag DV All variables are set to None at module initialization specifying that standard environment variables should be used connect Name connect open a connection to the database server Synopsis connect dbname host port opt tty user passwd Parameters dbname Name of connected database string None host Name of the server host string None port Port used by the database server integer 1 opt Options for the server string None 114 tty File or tty for optional debug output from backend string None user PostgreSQL user string None passwd Password for user string None Return Type pgobject If succ
399. ust appear in the same source file conventionally it s written just before the function itself This macro call is not needed for internal language functions since PostgreSQL currently assumes all internal functions are version 1 However it is required for dynamically loaded functions In a version 1 function each actual argument is fetched using a PG GETARG xxx macro that corre sponds to the argument s data type and the result is returned using a PG RETURN xxx macro for the return type Here we show the same functions as above coded in version 1 style include postgres h include lt string h gt include fmgr h By Value PG_FUNCTION_INFO_V1 add_one Datum add_one PG_FUNCTION_ARGS int32 arg PG_GETARG_INT32 0 PG RETURN INT32 arg 1 By Reference Fixed Length PG FUNCTION INFO V1 add one float8 Datum add one float8 PG FUNCTION ARGS The macros for FLOAT8 hide its pass by reference nature 188 float8 arg PG G Chapter 9 Extending SQL Functions ETARG FLOAT8 0 PG RETURN FLOAT8 arg 1 0 PG FUNCTION INFO V1 makepoint Datum makepoint PG FUNCTION ARGS Here the pass by reference nature of Point is not hidden Point pointx PG GETARG POINT P 0 Point pointy PG GETARG POINT P 1 Point new point Point palloc sizeof Point new point x pointx x new po
400. ust be within a transaction conn setAutoCommit false Get the Large Object Manager to perform operations with LargeObjectManager lobj org postgresql PGConnection conn getLargeObjectAPI create a new large object int oid lobj create LargeObjectManager READ LargeObjectManager WRITE open the large object for write LargeObject obj lobj open oid LargeObjectManager WRITE Now open the file File file new File myimage gif FileInputStream fis new FileInputStream file copy the data from the file to the large object byte buf new byte 2048 int s tl 0 whil s fis read buf 0 2048 gt 0 obj write buf 0 s tl s Close the large object obj close Now insert the row into imagesLO PreparedStatement ps conn prepareStatement INSERT INTO imagesLO VALUES ps setString 1 file getName ps setInt 2 oid ps executeUpdate ps close fis close Retrieving the image from the Large Object All LargeObject API calls must be within a transaction conn setAutoCommit false Get the Large Object Manager to perform operations with LargeObjectManager lobj org postgresql PGConnection conn getLargeObjectAPI PreparedStatement ps con prepareStatement SELECT imgOID FROM imagesLO WHERE imgname ps setString 1 myimage gif ResultSet rs ps executeQuery if
401. vail rsl sl avail AS total avail FROM shoe rsh shoelace rsl WHERE rsl sl_color rsh slcolor AND rsl sl_len_cm gt rsh slminlen_cm AND rsl sl_len_cm lt rsh slmaxlen_cm shoe_ready WHERE int4ge shoe_ready total_avail 2 Similarly the rules for shoe and shoelace are substituted into the range table of the sub query leading to a three level final query tree SELECT shoe_ready shoename shoe_ready sh_avail shoe_ready sl_name shoe_ready sl_avail shoe_ready total_avail FROM SELECT rsh shoename rsh sh_avail rsl sl_name rsl sl_avail min rsh sh_avail rsl sl_avail AS total_avail FROM SELECT sh shoename sh sh_avail lcolor lminlen lminlen un un fact AS slminlen cm lmaxlen lmaxlen un un fact AS slmaxlen cm DJ O2 0 0 20 O0 o oou un lunit AnD HAD HN tu FRO WHERE sh slunit un un name rsh hoe_data sh unit un SELECT s sl_name 224 Chapter 13 The Rule System s sl avail SysL color s sl len ssl umtu s sl len u un fact AS sl len cm FROM shoelace data s unit u WHERE s sl unit u un name rsl WHERE rsl sl color rsh slcolor AND rsl sl len cm gt rsh slminlen cm AND rsl sl len cm lt rsh slmaxlen cm shoe ready WHERE int4ge shoe ready total avail 2 It turns out that the planner will collapse this tree into a two level query tree the
402. vailable it opens one Once the thread has finished with it it returns it to the manager who can then either close it or add it to the pool The manager would also check that the connection is still alive and remove it from the pool if it is dead So with servlets it is up to you to use either a single connection or a pool The plus side for a pool is that threads will not be hit by the bottle neck caused by a single network connection The down side is that it increases the load on the server as a backend process is created for each Connect ion It is up to you and your applications requirements 5 9 Connection Pools And DataSources 5 9 1 JDBC JDK Version Support JDBC 2 introduced standard connection pooling features in an add on API known as the JDBC 2 0 Op tional Package also known as the JDBC 2 0 Standard Extension These features have since been included in the core JDBC 3 API The PostgreSQL JDBC drivers support these features with JDK 1 3 x in com bination with the JDBC 2 0 Optional Package JDBC 2 or with JDK 1 4 JDBC 3 Most application servers include the JDBC 2 0 Optional Package but it is also available separately from the Sun JDBC download site 2 http java sun com products jdbc download html spec 107 Chapter 5 JDBC Interface 5 9 2 JDBC Connection Pooling API The JDBC API provides a client and a server interface for connection pooling The client interface is javax sql DataSource which is what app
403. ven if the command given is an INSERT UPDATE or DELETE And they have different semantics from the others in that they modify the parse tree in place instead of creating a new one So SELECT rules are described first Currently there can be only one action in an ON SELECT rule and it must be an unconditional SELECT action that is INSTEAD This restriction was required to make rules safe enough to open them for ordinary users and it restricts rules ON SELECT to real view rules The examples for this document are two join views that do some calculations and some more views using them in turn One of the two first views is customized later by adding rules for INSERT UPDATE and DELETE operations so that the final result will be a view that behaves like a real table with some magic functionality It is not such a simple example to start from and this makes things harder to get into But it s better to have one example that covers all the points discussed step by step rather than having many different ones that might mix up in mind The database needed to play with the examples is named a1 bundy You ll see soon why this is the database name And it needs the procedural language PL pgSQL installed because we need a little min function returning the lower of 2 integer values We create that as CREATE BEGI Hy UNCTION min integer integer RETURNS integer AS IF 1 2 THEN RETURN 1 ND IF TURN 2 on Gl
404. verhead for a variable length type Now that we ve gone over all of the possible structures for base types we can show some examples of real functions 9 5 3 Version 0 Calling Conventions for C Language Functions We present the old style calling convention first although this approach is now deprecated it s easier to get a handle on initially In the version 0 method the arguments and result of the C function are just 185 Chapter 9 Extending SQL Functions declared in normal C style but being careful to use the C representation of each SQL data type as shown above Here are some examples include postgres h include lt string h gt By Value int add_one int arg return arg 1 By Reference Fixed Length floats add_one_float8 float8 arg floats result float8 result arg 1 0 return result Point makepoint Point pointx Point Point new_point Poin new point x pointx x new point y pointy gt y return new_point By Reference Variable Length text copytext text t VARSIZE is the total size x text new t text pallo VARATT SIZEP new t VARSIZ VARDATA is a pointer to t memcpy void VARDATA new palloc sizeof float8 pointy t palloc sizeof Point e of the struct in bytes C VARSIZE t E t he data region of the struct t
405. w Jdbc3PoolingDataSource source setDataSourceName A Data Source source setServerName localhost source setDatabaseName test source setUser testuser source setPassword testpassword source setMaxConnections 10 new InitialContext rebind DataSource source Then code to use a connection from the pool might look like this Connection con null try DataSource source DataSource new InitialContext lookup DataSource con source getConnection 111 Chapter 5 JDBC Interface use connection catch SQLException e log error catch NamingException e DataSource wasn t found in JNDI finally if con null try con close catch SQLException e 5 9 6 Specific Application Server Configurations Configuration examples for specific application servers will be included here 5 10 Further Reading If you have not yet read it I d advise you read the JDBC API Documentation supplied with Sun s JDK and the JDBC Specification Both are available from http java sun com products jdbc index html http jdbc postgresql org contains updated information not included in this document and also includes precompiled drivers 112 Chapter 6 PyGreSQL Python Interface Author Written by D Arcy J M Cain lt darcy druid net gt Based heavily on code written by Pascal Andre lt andre chimay via ecp fr gt Copyright 1995 Pascal Andre Fu
406. will also be changed in the future If successful SPI functions return a non negative result either via a returned integer value or in SPI result global variable as described below On error a negative or NULL result will be returned 17 1 Interface Functions SPI connect Name SPI connect Connects your procedure to the SPI manager Synopsis int SPI connect void Inputs None 260 SPI connect Outputs int Return status SPI OK CONNECT if connected SPI ERROR CONNECT if not connected Description SPI connect opens a connection from a procedure invocation to the SPI manager You must call this function if you will need to execute queries Some utility SPI functions may be called from un connected procedures If your procedure is already connected SPI connect will return an SPI ERROR CONNECT error Note that this may happen if a procedure which has called SPI connect directly calls another procedure which itself calls SPI connect While recursive calls to the SPI manager are permitted when an SPI query invokes another function which uses SPI directly nested calls to SPI connect and SPI finish are forbidden Usage Algorithm SPI connect performs the following Initializes the SPI internal structures for query execution and memory management 261 SPI finish Name SPI finish Disconnects your procedure from the SPI manager Synopsis SPI finish void Inputs None Outputs int
407. will be deemed most commonly useful and will be marked as the default operator class for that data type and index access method The same operator class name can be used for several different access methods for example both B tree and hash access methods have operator classes named oid ops but each such class is an independent entity and must be defined separately 242 Chapter 14 Interfacing Extensions To Indexes 14 3 Access Method Strategies The operators associated with an operator class are identified by strategy numbers which serve to identify the semantics of each operator within the context of its operator class For example B trees impose a strict ordering on keys lesser to greater and so operators like less than and greater than or equal to are interesting with respect to a B tree Because PostgreSQL allows the user to define operators PostgreSQL cannot look at the name of an operator e g lt or gt and tell what kind of comparison it is Instead the index access method defines a set of strategies which can be thought of as generalized operators Each operator class shows which actual operator corresponds to each strategy for a particular data type and interpretation of the index semantics B tree indexes define 5 strategies as shown in Table 14 1 Table 14 1 B tree Strategies Operation Strategy Number less than 1 less than or equal 2 equal 3 ereater than or equal 4 ereater
408. words list of syntax label column table language handler large object 32 LC COLLATE ldconfig length binary strings See binary strings length character strings See character strings length libperl libpgtcl 41 libpq 1 libpq fe h libpq int h libpython like limit line Linux locale locking log files MAC address See macaddr macaddr data type MacOS X make MANPATH See Also man pages max MD5 363 min multibyte names qualified unqualified namespaces NetBSD network addresses nextval nonblocking connection 13 nonrepeatable read not operator not in notice processor NOTIFY 16 54 nullif numeric constants numeric data type object identifier data type object oriented database obj description offset with query results OID opaque OpenBSD OpenSSL See Also SSL operators logical precedence syntax or operator Oracle 333 ORDER BY output function Index overlay overloading 202 password pgpass PATH path data type Perl 352 PGDATA PGDATABASE PGHOST PGPASSWORD PGPORT pgtcl closing 58 connecting 43 45 46 47 48 50 connection loss 55 creating 56 delete 63 export 65 import 64 notify 54 opening 57 positioning
409. y and reliability POSTGRES has been used to implement many different research and production applications These in clude a financial data analysis system a jet engine performance monitoring package an asteroid tracking database a medical information database and several geographic information systems POSTGRES has also been used as an educational tool at several universities Finally Illustra Information Technologies later merged into Informix which is now owned by IBM picked up the code and commercialized it POSTGRES became the primary data manager for the Sequoia 2000 scientific computing project in late 1992 The size of the external user community nearly doubled during 1993 It became increasingly obvious that maintenance of the prototype code and support was taking up large amounts of time that should have been devoted to database research In an effort to reduce this support burden the Berkeley POSTGRES project officially ended with Version 4 2 2 2 Postgres95 In 1994 Andrew Yu and Jolly Chen added a SQL language interpreter to POSTGRES Postgres95 was subsequently released to the Web to find its own way in the world as an open source descendant of the original POSTGRES Berkeley code Postgres95 code was completely ANSI C and trimmed in size by 25 Many internal changes improved performance and maintainability Postgres95 release 1 0 x ran about 30 50 faster on the Wisconsin 2 http www informix com 3 http
410. y point to an internal error 209 ECPG MISSING INDICATOR NULL value without indicator in line d A null value was returned and no null indicator variable was supplied 210 ECPG NO ARRAY Variable is not an array in line d An ordinary variable was used in a place that requires an array 211 ECPG DATA NOT ARRAY Data read from backend is not an array in line Sd The database returned an ordinary variable in a place that requires array value 220 ECPG NO CONN No such connection s in line d The program tried to access a connection that does not exist 71 Chapter 4 ECPG Embedded SQL in C 221 ECPG NOT CONN Not connected in line d The program tried to access a connection that does exist but is not open 230 ECPG INVALID STMT Invalid statement name s in line d The statement you are trying to use has not been prepared 240 ECPG UNKNOWN DESCRIPTOR Descriptor s not found in line d The descriptor specified was not found The statement you are trying to use has not been prepared 241 ECPG INVALID DESCRIPTOR INDEX Descriptor index out of range in line Sd The descriptor index specified was out of range 242 ECPG UNKNOWN DESCRIPTOR ITEM Descriptor s not found in line d The descriptor specified was not found The statement you are trying to use has not been prepared 243 ECPG VAR NOT NUMERIC Variable is not a numeric type in line
411. ypes Numeric types are set to O dates are set to today and everything else is set to the empty string If the array argument is present it is used as the array and any entries matching attribute names are cleared with everything else left unchanged 148 delete Name delete delete a row from a table Synopsis delete table a Parameters table Name of table a A dictionary of values Return Type none Description This method deletes the row from a table It deletes based on the OID as munged as described above 149 6 5 Query Result Object pgqueryobject getresult Name getresult get the values returned by the query Synopsis getresult Parameters none Return Type list List of tuples Exceptions SyntaxError Too many arguments pg error Invalid previous result Description getresult method returns the list of the values returned by the query More information about this result may be accessed using 1istfields fieldname and fieldnum methods 150 dictresult Name dictresult get the values returned by the query as a list of dictionaries Synopsis dictresult Parameters none Return Type list List of dictionaries Exceptions SyntaxError Too many arguments pg error Invalid previous result Description dictresult method returns the list of the values returned by the query with each tuple returned as a
412. yscache h include catalog pg proc h include catalog pg type h PG FUNCTION INFO V1l plsample call handler Datum plsample call handler PG FUNCTION ARGS Datum retval if CALLED AS TRIGGER fcinfo Called as a trigger procedure A TriggerData trigdata TriggerData fcinfo context retval else Called as a function if retval return retval Only a few thousand lines of code have to be added instead of the dots to complete the call handler See Section 9 5 for information on how to compile it into a loadable module The following commands then register the sample procedural language CREATE FUNCTION plsample_call_handler RETURNS language_handler AS usr local pgsql lib plsample LANGUAGE C CREATE LANGUAGE plsample HANDLER plsample_call_handler 205 Chapter 10 Extending SQL Types As previously mentioned there are two kinds of types in PostgreSQL base types defined in a program ming language and composite types This chapter describes how to define new base types The examples in this section can be found in complex sql and complex c in the tutorial directory Composite examples are in uncs sql A user defined type must always have input and output functions These functions determine how the type appears in strings for input by the user and output to the user and how the type is organized in memory Th

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