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PostgreSQL 7.2 Programmer`s Guide

1. DELETE FROM shoelace WHERE EXISTS SELECT FROM shoelace_candelet WHERE sl_name shoelace sl_name Voila al_bundy gt 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 sl7 6 brown 60 cm 60 sl14 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 a view with 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 16 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
2. spi_exec array C SELECT FROM pg_class elog DEBUG have table C relname 325 Chapter 24 PL Tcl Tcl Procedural Language will print a DEBUG log message for every row of pg_class This feature works similarly to other Tcl looping constructs in particular cont inue 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 names 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 int 4 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
3. 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 In putStream and OutputStream classes for this object 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 8 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 108 Chapter 8 JDBC Interface 8 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 SQLException Reads some data from the object and return as a byte array public int read byte buf int off int len throws SQLException Reads some data from the object into an existing array Parameters buf destination array off offset within array len number o
4. If you execute the above function it will reference the OID for my_function in the query plan produced for the PERFORM statement Later if you drop and re create my_function then pop ulate will not be able to find my_function anymore You would then have to re create pop ulate or at least start a new database session so that it will be compiled afresh 290 Chapter 23 PL pgSQL SQL Procedural Language 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 PL pgSQL EXECUTE statement at the price of constructing a new query plan on every execution 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 23 1 1 Advantages of Using PL pgSQL e Better performance see Section 23 1 1 1 SQL support see Section 23 1 1 2 e Portability see Section 23 1 1 3 23 1 1 1 Better Performance SQL is the language PostgreSQL and most other Relational Databases use as query language It s portable and eas
5. 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 PQnfields res for i 0 i lt nFields i printf 15s POQfname res i printf n n next print out the rows for i 0 i lt PQntuples res i for j 0 j lt nFields j printf S 15s PQgetvalue res i Jj printf n PQclear res close the cursor res PQexec conn CLOSE mycursor PQclear res commit the transaction res PQexec conn COMMIT 23 Chapter 1 libpq C Library PQclear res close the connection to the database and cleanup PQfinish conn fclose debug return 0 Example 1 2 libpq Example Program 2 testlibpgq2 c Test of the asynchronous notification interface Start this program then from psql in another window do NOTIFY TBL2 FF F F F Or if you want to get fancy try this Populate a database with the following CREA ABLE TBL1 i int4 F FF F F E CREATE TABLE TBL2 i int4 CREATE RULE rl AS ON INSERT TO TBL1 DO INSERT INTO TBL2 values new i NOTIFY TBL2 and do F HF INSERT INTO TBL1 values 1
6. PQresultStatus can return one of the following values Chapter 1 libpg C Library 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_TUPLES_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 UPDATE etc A response of PGRES_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 PQresultErrorMessage returns the error message associated with the query or an empty string if there was no error char PQresultErrorMessage const PGresult res Immediately following a PQexec or PQgetResult call PQerrorMessage on the connection will return the same stri
7. 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 result t ype 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 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 93 Chapter 8 JDBC Interface 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 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 addFunct ions method which is based upon a query rather than hard coding
8. T elog NOTICE 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 gt SELECT execq CREATE TABLE a x INTEGER 0 vac gt INSERT INTO a VALUES execq INSERT INTO a VALU INSERT 167631 1 vac gt SELECT execq SELECT FROM a 0 NOTICE EXECQ 0 lt lt lt inserted by execq E S 0 0 NOTICE EXECQ 1 lt lt lt value returned by execq and inserted by upper INSERT vac gt SELECT execq INSERT INTO a SELECT x 2 FROM a 1 vac gt SELECT execq SELECT FROM a 10 NOTICE EXECQ 0 NOTICE EXECQ 1 NOTICE 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 285 Chapter 21 Server Programming Interface vac gt DELETE FROM a DELETE 3 vac gt INSERT INTO a VALU INSERT 167712 1 vac gt SELECT FROM a EJ S execq SELECT FROM a 0 1 1 lt lt lt no tuples ina 0 1 1 row vac gt INSERT INTO a VALUES execq SELECT FROM a 0
9. ECLAR y v_host v_path _url ALIAS FOR VARCHAR VARCHAR 1 a_posl IN EGER a_pos2 IN EGER a_pos3 IN EGIN v_host a_posl IF a_posl RETURN END IF a_pos2 IF a_pos2 v_host v_path R D IF ie host RETUR LANGUAGI E pl EGER NULL substr v_url substr v_url Chapter 23 PL pgSQL SQL Procedural Langu TT Y PostgreSQL doesn t have an instr fu a posl 2 a_posl 2 a_posl 2 ror for a_pos2 a_posl 2 a_pos2 1 a_pos2 a_pos2 a_posl a_pos2 a_posl 1 Here is how this procedure could be translated for PostgreSQL RETURNS VARCHAR AS cs_parse_url_host VARCHAR instr v_url 0 THEN wes Return a blank instr v_url a_posl 2 0 THEN a Jr r ETURN v_host substr v_url vy hosts pgsql substr v_ url a_posl 2 a_posl 2 a_pos2 a_posl 2 age nction 316 Chapter 23 PL pgSQL SQL Procedural Language Note PostgreSQL does not have an instr function so you can work around it using a combina tion 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 23 11 6 for the code 23 11 3 Procedures Oracle procedures give a little more flexibility to the devel
10. 8 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 8 7 3 2 2 Methods public LargeObject open int oid throws SQLException 110 Chapter 8 JDBC Interface 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 e 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 e public void unlink int oid throws SQLException This deletes a large object It is identical to the delete method and is supplied as the C API uses unlink 8 8 Using the driver in a multi threaded or a servlet environment A problem with many JDBC drivers is that only one thread can use a Connect ion at any one time otherwise a thread could send a query
11. include libpq fe h include utils geo_decls h for the POLYGON type void exit_nicely PGconn conn PQfinish conn exit 1 main char pghost pgport pgoptions pgtty char dbName int nFields 26 Chapter 1 libpq C Library int iz j int i_fnum d_fnum p_fnum 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 R 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 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 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 PQclear
12. lobjOid importFile conn in_filename lobjOid lo_import conn in_filename printf as large object d n lob jOid printf picking out bytes 1000 2000 of the large object n pickout conn lob jOid 1000 1000 printf overwriting bytes 1000 2000 of the large object with X s n overwrite conn lob jOid 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 PQclear res PQfinish conn exit 0 37 Chapter 3 libpq C Binding Library 3 1 Introduction libpq is the C API to PostgreSQL libpq is a set of classes that allow client programs to connect to the PostgreSQL backend server These connections come in two forms a database class and a large object class The database class is intended for manipulating a database You can send all sorts of SQL queries and commands to the PostgreSQL backend server and retrieve the responses of the server The large object class is intended for manipulating a large object in a database Although a large object instance can send normal queries to the PostgreSQL backend server it is only intended for simple queries that do not return any data A large object should be seen as a file stream In the future it should behave much like the C file streams cin cout and cerr This chapter is based on the documentation for
13. 2 I built the example sources right under pgsql src just extracted the tar file there The aforemen tioned Makefile assumes it is one level below pgsql src in our case in pgsql src pggist 3 The changes I made to the c files were all about include s function prototypes and typecasting Other than that I just threw away a bunch of unused vars and added a couple parentheses to please gcc I hope I did not screw up too much 4 There is a comment in polyproc sql there s a memory leak in rtree poly_ops 5 ftp s2k ftp cs berkeley edu pub gist pggist pggist tgz 6 http gist cs berkeley edu 8000 gist 237 Chapter 19 GiST Indexes CREATE INDEX pix2 ON polytmp USING RTREE p poly_ops Roger that I thought it could be related to a number of PostgreSQL versions back and tried the query My system went nuts and I had to shoot down the postmaster in about ten minutes I will continue to look into GiST for a while but I would also appreciate more examples of R tree usage 238 Chapter 20 Triggers PostgreSQL has various server side function interfaces Server side functions can be written in SQL PLPGSQL TCL or C Trigger functions can be written in any of these languages except 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
14. 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 0 185 Chapter 12 Extending SQL Functions 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 floats8 arg PG_GETARG_FLOATS8 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 gt x pointx gt x new_point gt 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 xt PG_GETARG_TEXT_P 0 VARSIZE is the total size of the struct in bytes XY text new_t text palloc VARSIZE t VARATT_SIZEP new_t VARSIZE t VARDATA is a pointer to the data region of the struct XY memcpy void VARDATA new_t destination vo
15. IF ea iw RETURN 0 END LANGUAGE plpgsql Notice how you can raise notices or errors in PL pgSQL 23 11 4 Packages Note haven t done much with packages myself so if there are mistakes here please let me know 318 Chapter 23 PL pgSQL SQL Procedural Language 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 e 99 dot Here is an example of an Oracle package from ACS 4 the ArsDigita Community System CREATE OR REPLACE PACKAGE BODY acs AS FUNCTION add_user user_id IN users user_idsTYPE DEFAULT NULL object_type IN acs_objects object_type sTYPE DEFAULT user creation_date IN acs_objects creation_date TYPE DEFAULT sysdate creation_user IN acs_objects creation_user sTYPE DEFAULT NULL creation_ip IN acs_objects creation_ip sTYPE DEFAULT NULL RETURN users user_id TYPE Is v_user_id users user_id STYPE v_rel_id membership_rels rel_id TYPE BEGIN v_user_id acs_user new user_id object_type creation_ip creation_date creation_user RETURN v_user_id END END acs show errors email We port this to PostgreSQL by creating the different objects of the Oracle package as functions with
16. In this example the JVM will attempt to load the driver as part of its initialization Once done the ImageViewer 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 SQLException being thrown this is probably caused by the driver not being in the class path or the value in the parameter not being correct 8 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 85 Chapter 8 JDBC Interface host The host name of the server Defaults to localhost port The port number the server is listening on Defaults to the PostgreSQL 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 DriverManager getConnection method Connection db DriverManager getConnection url username password 8 2 4 Closing the Connection To close the database connection simply call the close method to the Connection db close 8 3 Issuing a Qu
17. 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 146 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 types Numeric types are set to 0 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 147 delete Name delete deletes the 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 148 9 5 Query result object pgqueryobject getresult Name get result gets the values returned by the query Synopsis getresult Parameters none Return Type list List of tuples E
18. When writing a bug report please choose non confusing terminology The software package in to tal 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 pro grams 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 xviii Preface 5 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 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 form available at the project s 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
19. exec sql begin declare section int index int result xec sql end declare section exec sql select res into result from mytable where index index is translated into Processed by ecpg 2 6 0 These two include files are added by the preprocessor include lt ecpgtype h gt include lt ecpglib h gt exec sql begin declare section line 1 foo pgce int index int result exec sql end declare section ECPGdo __LINE__ NULL select res from mytable where index My 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 74 Chapter 6 ecpg Embedded SQL in C 6 6 3 The Library The most important function in the library is ECPGdo It takes a variable number of arguments Hope fully 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 modified by the input variables i e the variables that where not k
20. is BEFORE you may return None or OK from the Python function to indicate the tuple is unmodified SKIP to abort the event or MODIFIED to indicate you ve modified the tuple The PL Python language module automatically imports a Python module called plpy 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 error msg plpy fatal msg plpy debug msg and plpy notice msg They are mostly equivalent to calling elog LEVEL msg where LEVEL is DEBUG ERROR FATAL or NOTICE plpy error and plpy fatal actually raise 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 or plpy fatal 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 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 re
21. 20 1 Trigger Creation If a trigger event occurs the trigger manager called by the Executor sets up a TriggerData informa tion structure described below and calls the trigger function to handle the event The trigger function must be defined before the trigger is created as a function taking no arguments and returning opaque If the function is written in C it must use the version 1 function manager interface The syntax for creating triggers is as follows 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 name of the trigger is used if you ever have to delete the trigger It is used as an argument to the DROP TRIGGER command BEFORE AFTER Determines whether the function is called before or after the event INSERT DELETE UPDATE The next element of the command determines on what event s will trigger the function Multiple events can be specified separated by OR relation The relation name determines 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 procedure The procedure name is the function called 239 Chapter 20 Triggers args The argument
22. 21 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_LERROR_NOATTRIBUTE if the named attribute is not found Description SPI_fnumber returns the attribute number for the attribute with name in fname Usage Attribute numbers are 1 based If the given fname refers to a system attribute eg oid then the appropriate negative attribute number will be returned The caller should be careful to test for exact equality to SPI_LERROR_NOATTRIBUTE to detect error testing for result lt 0 is not correct unless system attributes should be rejected 264 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 SPILERROR_NOATTRIBUTE on error Description SPI_f
23. 23 6 2 1 IF 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 lt gt 0 THEN UPDATE users SET email v_email WHERE user_id v_user_id END IF 301 Chapter 23 PL pgSQL SQL Procedural Language 23 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 THE return fullname ELSE return hp_true_filename parentid fullname END IF IF v_count gt 0 THEN INSERT INTO users_count count VALUES v_count return t ELSE return f END IF 23 6 2 3 IF THEN ELSE IF 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 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
24. 8 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 8 7 1 Accessing the Extensions To access some of the extensions you need to use some extra methods in the org postgresql Connection class In this case you would need to case the return value of Driver getConnection For example Connection db Driver getConnection url username password Ke later on Fastpath fp org postgresql Connection db getFastpathAPI 8 7 1 1 Class org postgresql Connection public class Connection extends Object implements Connection java lang Object org postgresql Connection These are the extra methods used to gain access to PostgreSQL s extensions Methods defined by java sql Connection are not listed 8 7 1 1 1 Methods public Fastpath getFastpathAPI throws SQLException This returns 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 9 Chapter 8 JDBC Interface Fastpath fp org postgresql Connection myconn g
25. Return Type none Exceptions TypeError Too many any arguments Description reset method resets the current database 128 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 129 fileno Name fileno returns 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 underlying socket id used to connect to the database This is useful for use in select calls etc 130 getnotify Name getnotify gets 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 tup
26. lobjlId 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_lo_import reads the specified file and places the contents into a large object Usage pg_lo_import must be called within a BEGIN END transaction block 64 pg_lo_ export Name pg_lo_export export a large object to a file Synopsis pg_lo_export conn lobjId filename Inputs conn Specifies a valid database connection lobjlId Large object identifier filename Unix file name Outputs None Description pg_lo_export writes the specified large object into a Unix file Usage pg_lo_export must be called within a BEGIN END transaction block 65 Chapter 5 libpgeasy Simplified C Library Author Written by Bruce Momjian lt pgman candle pha pa us gt and last updated 2000 03 30 pgeasy allows you to cleanly interface to the libpq library more like a 4GL SQL interface Refer to Chapter 1 for more information about libpq It consists of set of simplified C functions that encapsulate the functionality of libpq The functions are PGresult doquery char query PGconn connectdb char options void disconnectdb et fe
27. memmove char amp pval gt npts PQgetvalue res i p_fnum plen printf tuple d got n i printf i d bytes d n PQgetlength res i i_fnum ival printf d d bytes f n PQgetlength res i d_fnum dval printf p d bytes d points tboundbox hi f f lo f f n PQgetlength res i d_fnum pval gt npts pval gt boundbox xh pval gt boundbox yh pval gt boundbox xl pval gt boundbox yl 28 Chapter 1 libpg C Library PQclear res close the cursor res PQexec conn CLOSE mycursor PQclear res commit the transaction res PQexec conn COMMIT PQclear res close the connection to the database and cleanup PQfinish conn return 0 29 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 the 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 fil
28. port 5432 datnames is the list to be result 45 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 res 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 S datnames 4 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 Idconfig 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 information libpgtcl in turn depends on libpq so the dynamic loader must also be able to find the libpg 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
29. shoelace_ok OLD shoelace_ok NEW shoelace s shoelace bpchareq s bpchareq s n n hoelac EW shoelace OLD shoelace_data showlace_data oelace sl_name showlace_arrive arr_name oelace_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 system isn t finished with this loop so it continues and applies the rule R ETs UPDATE FROM shoelace_data SI sl_name s sl_avail sl_color sl_len s sl_unit s shoelace_ar hoelace on it and we get ET sl_name int4pl s sl_avail shoelace_arrive arr_quant s sl_color sl_len Sl_unit rive shoelace_arrive shoelace_ok shoelace_ok shoelace_ok OLD shoelace_ok NEW 221 WH ERE AND Chapter 16 The Rule System shoelace shoelace shoelace OLD shoelace NEW shoelace_data showlace_data shoelace OLD shoelace NEW shoelace_data s unit u bpchareq s sl_name showlace_arrive arr_name bpcharegq shoelace_data sl_name s sl_name 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 what produces the extra parse tree INS F WH ERT ROM ERE AND AND INTO shoelace_log SELECT s sl_name int4pl s sl_avail shoelace_arrive a
30. And it depends on the overall size of the software table if the rule will still be faster in the sequential scan 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 gt Index Scan using comp_manufidx on computer gt 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 alw
31. DO INSTEAD shoelace_arrive char 10 integer shoelace_ok char 10 integer shoelace_ok_ins AS ON INS UPDATE shoelace SET sl_avail sl_avail NEW ok_quant WHERE sl_name NEW ok_name al_bundy gt SEL arr_name arr_quant s13 sl6 s18 3 rows 10 20 20 ECT FROM shoelace_arrive ERT TO shoelace_ok is exactly what s on the part list We take a quick look at the current data al_bundy gt 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 s1l7 6 brown 60 cm 60 s13 0 black 35 inch 88 9 s14 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 gt INS and check the results ERT INTO shoelace_ok SELECT FROM shoelace_arrive al_bundy gt 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 s12 6 black 100 cm 100 sl7 6 brown 60 cm 60 s14 8 black 40 inch 101 6 s13 10 black 35 inch 88 9 220 Chapter 16 The Rule System s18 21 brown 40 inch 101 6 s15 4 brown 1 m 100 sl6 20 brown 0 9 m 90 8 rows al_bundy gt SELECT FROM shoelace_log sl_name sl_avail lo
32. 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 have its oid 137 loimport Name loimport imports 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 138 9 4 Database wrapper class DB pkey pg module contains a class called DB All pgobject methods are 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 S 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 variabl
33. 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 152 fieldnum Name fieldnum field name number conversion 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 used to build a function that con verts result list strings to their correct type using a hardcoded table definition The number returned is the field rank in the result values list 153 ntuples Name ntuples returns 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 154 9 6 Large Object pglarge 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 cal
34. Oracle s single tasking Oracle version 7 0 on AIX 3 uses OS supported locks in shared memory that allow an application designer to link an application in a single tasking way Instead of starting one client process per application process both the database part and the application part run in the same process In later versions of Oracle this is no longer supported This would require a total redesign of the PostgreSQL access model and the performance gain does not justify the effort 6 5 Porting From Other RDBMS Packages The design of ecpg follows the SQL standard Porting from a standard RDBMS should not be a prob lem Unfortunately 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 precompiler 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 INIFROM cursor Oracle however does not use the keywords IN or FROM This feature cannot be added since it would create parsing conflicts 6 6 For the Developer This section explain how ecpg works internally It contains valuable information to help users under stand how to use ecpg 6 6 1 The Prep
35. PL pgSQL SQL Procedural Language 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 END RETURN 0 ELSE 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 gt 0 LOOP temp_str substring string FROM beg FOR ss_length pos position string_to_search IN temp_str IF pos gt 0 THEN occur_number occur_number 1 IF occur_number occur_index THEN RETURN beg END IF END LOOP RETURN 0 END IF T GUAGE plpgsql 322 Chapter 24 PL Tcl Tcl Procedural Language PL Tcl is a loadable procedural language for the PostgreSQL database system that enables the Tcl language to be used to write functions and trigger procedures This package was originally written by Jan Wieck 24 1 Overview PL Tcl offers most of the capabilities a function writer has in the C language except for some restric tions 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 avail
36. 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 te tag DV All variables are set to None at module initialization specifying that standard environment variables should be used connect Name connect opens 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 tty File or tty for optional debug output from backend string None user PostgreSQL user string None passwd Password for user string None 114 connect Return Type pgobject If successful 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 all exceptions relative to object allocation Description This method opens a connection to a specified database on a given PostgreSQL server You can use keywords here as described in the Python tutorial The names of the keywords are
37. 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 ordinary SQL command Sub sequently arrival of NOTIFY messages can be detected by calling Ponotifies PQnotifies 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 re turned from PQnotifies it is considered handled and will be removed from the list of notifications PGnotify PQnotifies PGconn conn 15 Chapter 1 libpg C Library typedef struct pgNotify char relname NAMEDATALEN name of relation containing data int be_pid process id of backend PGnotify After processing a PGnotify object returned by PQnotifies be sure to free it with free to avoid a memory leak Note In PostgreSQL 6 4 and later the be_pida 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 PQnotifies does not actually read backend data it just returns messages previously absorbed by another libpq function In prior releases of libpq the only way to ensure timely receipt of NOT
38. before any other system or user header files Including postgres h will also include elog h and palloc h for you e 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 e Compiling and linking your object code so that it can be dynamically loaded into PostgreSQL always requires special flags See Section 12 5 7 for a detailed explanation of how to do it for your particular operating system 12 5 7 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 Id 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 files are com piled into object files then the object files are linked together The object files need to be creat
39. future 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 rules CREATE RULE shoelace_ins AS ON INSERT TO shoelace DO INSTEAD INSERT INTO shoelace_data VALUES NEW sl_name NEW sl_avail NEW sl_color NEW sl_len NEW sl_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 219 Chapter 16 The Rule System 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 CR CR CR Now AI can sit down and do whatever until EATE TABLE arr_name arr_quant TABLE fe k_ name fe k_ quant EATE RULE
40. int4ne NEW sl_avail OLD sl_avail bpchareg shoelace_data sl_name s17 NEW sl_name current_user FRO WHERE AND Step 4 substitutes NEW references by the target list entries from the original parse tree or with the matching variable references from the result relation INS ERT shoelace_data current_user FROM shoelace_data shoelace_data int4ne 6 WHERE AND sil_name current_ NEW s INTO shoelace_log VALUES 6 timestamp hoelace_data OLD shoelace_data OLD sl_avail bpchareq shoelace_data sl_name sl7 Step 5 changes OLD references into result relation references INSERT INTO shoelace_log VALUES 217 F RO shoelace_data current_user shoelace_data shoelace_data Chapter 16 The Rule System 6 current_timestamp NEW shoelace_data OLD shoelace_data sl_name WH ERE AND int4ne 6 bpchareq shoelace_data sl_name shoelace_data sl_avail TEEGA 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 INTO shoelace_log VALUES shoelace_data sl_name 6 current_user current_timestamp FROM shoelace_data WHERE 6 shoelace_data sl_avail AND shoelace_data sl_name sl7 UPDATE shoelace_data SET
41. java lang Object org postgresql fastpath Fastpath 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 92 Chapter 8 JDBC Interface import org postgresql fastpath Then in your code you need to get a Fast Path object Fastpath fp org postgresql Connection 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 Connect ion is required as the get Fast 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 8 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 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
42. 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 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 107 Chapter 8 JDBC Interface Overrides clone in class PGobject public String getValue Returns the PGpolygon in the syntax expected by PostgreSQL Overrides getValue in class PGobject 8 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 LargeObjectManager which deals with creating opening and deleting large objects and LargeOb ject which deals with an individual object 8 7 3 1 Class org postgresql largeobject LargeObject public class LargeObject extends Object java lang Object
43. shared library This library is included with the ApplixWare distribution but axnet cnf needs to be modified to point to the correct location As root edit the file applixroot applix axdata axnet cnf a At the bottom of axnet cnf find the line that starts with libFor elfodbc ax b Change line to read libFor elfodbc applixroot applix axdata axshlib lib which will tell elfodbc to look in this directory for the ODBC support library Typically Applix is installed in opt so the full path would be opt applix axdata axshlib 1lib but if you have installed Applix somewhere else then change the path accordingly 2 Create odbc ini as described in Section 7 3 You may also want to add the flag TextAsLongVarchar 0 to the database specific portion of odbc ini so that text fields will not be shown as BLOB Testing ApplixWare ODBC Connections 1 Bring up Applix Data 2 Select the PostgreSQL database of interest a Select Query gt Choose Server b Select ODBC and click Browse The database you configured in odbc ini should be shown Make sure that the Host field is empty if it is not axnet will try to contact axnet on another machine to look for the database 79 Chapter 7 ODBC Interface c Select the database in the box that was launched by Browse then click OK d Enter user name and password in the login identification dialog and click OK You should see Starting elfodbc server in the lower le
44. that string 10 When you want two a_output a_outpytf y_ lt if gt vlik el re single quotes in the fer lt gt then resulting string which rer_keys kind f etker1t gt re accounts for 8 quotes fer end if land terminate that rer_keys key_string then re string 2 more You turn re will probably only need fer that if you were using a rer_keys referrer_typ 2s end TEs function to generate lother functions like in IExample 23 6 23 11 2 Porting Functions Example 23 5 A Simple Function Here is an Oracle function CREATE OR R char RETURN varchar IS BEGI IF v_version IS NULL THEN RETURN v_name END IF RETURN v_name END SHOW ERRORS v_version EPLACE FUNCTION cs_fmt_browser_version v_name IN varchar v_version IN var 313 Chapter 23 PL pgSQL SQL Procedural Language Let s go through this function and see the differences to PL pgSQL e PostgreSQL does not have named parameters You have to explicitly alias them inside your func tion e 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 pa rameters and functions can return only a single value e The RETURN key word in the function prototype not the function body becomes RETURNS in PostgreSQL e On Postg
45. tupdesc 1 amp isnull if isnull rettuple NULL return PointerGetDatum rettuple Now compile and create the trigger function CREATE FUNCTION trigf RETURNS OPAQUE AS path_to_so LANGUAGE C CREATE TABLE ttest x int4 vac gt CREATE TRIGGER tbefore BEFORE INSERT OR UPDATE OR DELETE ON ttest FOR EACH ROW EXECUTE PROCEDURE trigf ac gt CREATE RIGGER tafter AFTER INSERT OR UPDATE OR DELETE ON ttest OR EACH ROW EXECUTE PROCEDURE trigf ac gt INSERT INTO ttest VALUES NULL OTICE trigf fired before there are 0 tuples in ttest Cc v F CREATE v N I NSERT 0 0 Insertion skipped and AFTER trigger is not fired vac gt SELECT FROM ttest x 0 rows vac gt INSERT INTO ttest VALUES 1 NOTICE trigf fired before there are 0 tuples in ttest NOTICE trigf fired after there are 1 tuples in ttest AKRKAAAKAAA remember what we said about visibility INSERT 167793 1 vac gt SELECT FROM ttest 244 1 Chapter 20 Triggers row vac gt INSERT INTO ttest SELECT x 2 FROM ttest NO ICE trigf fired before there are 1 tuples in ttest NO ICE trigf fired after there are 2 tup
46. 0 fprintf stderr can t open large object d n lobjId open the file to be written to Ry 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 lobj_fd buf BUFSIZE gt 0 tmp write fd buf nbytes if tmp lt nbytes fprintf stderr error while writing s n filename void lo_close conn lob j_fd void close fd return void exit_nicely PGconn conn PQfinish conn exit 1 r int main int argc char argv char xin_filename out_filename char database Oid lobjOid PGconn oonny PGresult res r 36 Pop Chapter 2 Large Objects 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_filename argv 3 set up the connection EY 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 PQclear res printf importing file s n in_filename
47. 1 NOTICE 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 NOTICE EXECQ NOTICE EXECQ NOTICE EXECQ NOTICE EXECQ NOTICE EXECQ INSERT 0 2 vac gt SELECT FROM a x NNR N lt lt lt 3 tuples 2 1 just inserted 2 x in second tuple 4 rows RAKAKRAARA tuples visible to execq in different invocations F 2 2 lt lt lt 2 tuples 1 x in first tuple 6 286 lil Procedural Languages This part documents the procedural languages available in the PostgreSQL distribution as well as general issues concerning procedural languages Chapter 22 Procedural Languages 22 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 a
48. Again some of your OID numbers will almost certainly be different The operators we are interested in are those with OIDs 277970 through 277974 The values you get will probably be different and you should substitute them for the values below We will do this with a select statement Now we are ready to insert entries into pg_amop for our new operator class These entries must associate the correct B tree strategy numbers with each of the operators we need The command to insert the less than operator looks like INSERT INTO pg_amop amopclaid amopstrategy amopreqcheck amopopr SELECT opcl oid 1 false c opoid FROM pg_opclass opcl complex_ops_tmp c WHERE opcamid SELECT oid FROM pg_am WHERE amname btree AND opcname complex_abs_ops AND 232 Chapter 17 Interfacing Extensions To Indexes c oprname lt Now do this for the other operators substituting for the 1 in the second line above and the lt in the last line Note the order less than is 1 less than or equal is 2 equal is 3 greater than or equal is 4 and greater than is 5 The field amopreqcheck is not discussed here it should always be false for B tree operators The final step is the registration of the support routine previously described in our discussion of pg_am The OID of this support routine is stored in the pg_amproc table keyed by the operator
49. Books Judith Bowman Sandra Emerson and Marcy Darnovsky The Practical SQL Handbook Using Struc tured 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 Sci ence Press 1988 PostgreSQL Specific Documentation Stefan Simkovics Enhancement of the ANSI SQL Implementation of PostgreSQL Department of Information Systems Vienna University of Technology November 29 1998 Discusses SQL history and syntax and describes the addition of INTERSECT and EXCEPT con structs 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 POSTGR
50. 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 tl 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 213 Chapter 16 The Rule System 16 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 used twice with different names 16 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
51. 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 meaningful 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 OPAQUE AS switch STG_op INSERT set NEW S 1 0 UPDATE set NEW 1 OLD
52. Function CallInfoData 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 information This is a template for a PL handler written in C include postgres h 193 Chapter 12 Extending SQL Functions include executor spi h include commands trigger h include utils elog h include fmgr h include access heapam h include utils syscache h include catalog pg_proc h include catalog pg_type h PG_FUNCTION_INFO_V1 plsample_call_handler Datum plsample_call_handler PG_FUNCTION_ARGS Datum retval if CALLED_AS_TRIGGER fcinfo Called as a trigger procedure Poy TriggerData trigdata TriggerData fcinfo gt context retval else Called as a function 7 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 12 5 for information on how to compile it into a loadable module The following commands then register the sample procedural language CREATE FUNC LANGUAGI CREATE LANG TION plsample_call_handler RETURNS opaque AS usr local pgsql lib plsample B C UAGE plsample HANDLER plsample_call_handler 194 Chapter 13 Extending SQL Types As previously mention
53. IF v referrer_key kind LIKE referrer_key key_string THEN RETURN referrer_key referrer_typ Es END LEY END LOOP a_output a_output RETURN NULL END 314 ECUT IMM p EDIAT ND n now errors Chapter 23 PL pgSQL SQL Procedural Language a_output Here is how this function would end up in PostgreSQL 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 v_url ALIAS FOR 3 BEGIN Notice how we scan through the results of a query in a FOR loop using the FOR lt record gt 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 veferrer_keys key_string THEN RETURN veferrer_keys referrer_typ jl Pee END LB go END LOOP a_output a_output RETURN NULL END LANGUAGE plpgsql This works because we are not substituting any variables Otherwise
54. INS ERT INTO a SE I ECT 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_trigtuple 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 242 Chapter 20 Triggers 20 4 Examples There are more complex examples in src test regress regress c and in contrib spi Here is a very simple example of trigger usage Function trigf reports the number of tuples in the triggered relation ttest and skips the operation if the query attempts to insert NULL 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 HeapTuple rettupl
55. NEW and OLD These are needed so that they can be referenced by variables in the INSERT command s querytree 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_avail current_user current_timestamp FROM shoelace_data NEW shoelace_data OLD shoelace_data shoelace_data NEW sl_name 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_avail current_timestamp shoelace_data NEW shoelace_data OLD shoelace_data shoelace_data int4ne NEW sl_avail OLD sl_avail NEW sl_name current_user FROM WHERE 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 by the original parse tree INSERT INTO shoelace_log VALUES NEW sl_avail current_timestamp shoelace_data NEW shoelace_data OLD shoelace_data shoelace_data
56. Oracle PL SQL sseeesssesesssesseeseseessressrrrsrerrsresrsresrerrnreesrenerensenens 312 23 011 Main Differences creo n eee cd E E EA 312 23 11 1 1 Quote Me on That Escaping Single Quotes eee 312 23 112 Potins FUNCH ONS hersenen eeste reppe pE EE EEE NEE PERES ERENS 313 23113 Procedures 4 125 n eae E E eae es 317 23 11 4 Packages csiiacieoia nae iene he aveina dine anelee as 318 23 11 5 Other Things to Watch Fore cee ec eeeeeecsesseceeceeceseeeeeeeeeseesaeceeneensees 319 23 11 35 1 EXECUTE secs E a eeren ete aere a ri E Eko era pa RERO EESE sE 320 23 11 5 2 Optimizing PL pgSQL FunctionS e sesseeeeesseeerseereersreerreeserees 320 23 11 6 AppendiK a ri re eeraa aa r aa AE akan eas 320 23 11 6 1 Code for my instr functions eseseseeseeeessererseesreersreeerreseees 320 24 PL Tcl Tel Procedural Lam guage ccs seccessccsssss dshacbssegs iceesasbcesscesnss sou sssedessevcsgeaseevseey 323 DAV OVETVIEW raeo ae a ou Raabe tes eoi oes Stele en E EEE Oa cvtcis ones ewisaes Ghee 323 24 2 DESCLIPUON nse casei asec PAG scene ee Alte a Hei ae tiee ee 323 24 2 1 PL Tcl Functions and Arguments 20 00 eee ceecesceseeeeeeeeeseeseecaeeneennees 323 24 2 2 Data Values tn RIL T CI sic siecd sh ses ssstesescectevepscoet ta scesctesesh jeesspeaatesseesveeasoessess 324 24 2 3 Global Data in PL T C1 eee eecceeseeeeeeeceeseecneceeeeseeseveaseseenaecaeensenees 324 24 2 4 Database Access from PL T Cl eee ecee
57. 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 98 Chapter 8 JDBC Interface This must be overridden to allow the object to be cloned Overrides clone in class PGobject public String getValue Returns the PGcircle in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGline java lang Object org postgresql util PGobject ta 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 y1 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 first point p2 second point public PGline String s throws SQLException Parameters 99 public Methods public syntax public public public Chapter 8 JDBC Interface s definition of the line in PostgreSQL s syntax Throws SQLExcepti
58. SQL Procedural Language e 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 console use psql 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 end LANGUAGE plpgsql While running psql you can load or reload such a function definition file with i 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 23 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 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 blo
59. TYPE and SROWTYPE 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 vari ables 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 STYPE 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 definition tablesSROWTYPE oe ROWTYPE 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 D ECLARE users_rec users sROWTYPE user_id users user_id STYPE BEGIN user_id users_rec user_id CREATE FUNCTION does_view_exist INTEGER RETURNS bool AS DECLARE key ALIAS FOR 1 table_data cs_materialized_views ROWTYPI zal 295 Chapter 23 PL pgSQL SQL Procedural Language BEGIN SELECT INTO table_data FROM cs_materialized_views WHERE sort_key key IF NOT FOUND THEN RETURN
60. 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 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 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 usually named plper1u In this case the full Perl language is available 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 25 2 Building and Installing PL Perl If the with per1 option was supplied to the configure script the PostgreSQL build process will attempt to build the PL Perl shared library and install it in the PostgreSQL library directory On most platforms since PL Perl is a shared library the 1ibper1 library must be a shared library also At the time of this writing this is almost never the case in prebuilt Perl p
61. be a good time to start doing so 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 prepack aged distribution that starts the database server at boot time you should try to find out how that is done 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 versionandpsql 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 sourc
62. 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 func tion 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 behavior is not portable You might get a run time linker error or one of the functions will get called usually the internal one The al ternative form of the As clause for the SQL CREATE FUNCTION co
63. check for NULL inputs in the function code Without this we d have to check for NULLs explicitly for example by 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 12 5 4 Version 1 Calling Conventions for C Language Functions The version calling convention relies on macros to suppress most of the complexity of passing arguments 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_V1 funcname must 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 cor responds to the argument s datatype and the result is returned using a PG_RETURN_xxx macro for the return type
64. class OID and the support routine number First we need to register the function in PostgreSQL recall that we put the C code that implements this routine in the bottom of the file in which we implemented the operator routines Hy CREATE FUNCTION complex_abs_cmp complex complex RETURNS integer AS PGROOT src tutorial complex LANGUAGE C SELECT oid proname FROM pg_proc WHERE proname complex_abs_cmp oid proname 277997 complex_abs_cmp 1 row Again your OID number will probably be different We can add the new row as follows INSERT INTO pg_amproc amopclaid amprocnum amproc SELECT opcl oid 1 p oid FROM pg_opclass opcl pg_proc p WHERE opcamid SELECT oid FROM pg_am WHERE amname btree AND opcname complex_abs_ops AND p proname complex_abs_cmp And we re done Whew It should now be possible to create and use B tree indexes on complex columns 233 Chapter 18 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
65. configure command line e g configure prefix xxx with java This will build and install the driver along with the rest of the PostgreSQL package when you issue the make gmake and make gmake install commands If you only want to build the driver and not the rest of PostgreSQL change into the directory src interfaces jdbc and issue the respective make gmake command there Refer to the PostgreSQL installation instructions for more information about the configuration and build process When building the driver from source the jar file that is created will be named postgresql jar The build will create this file in the src interfaces jdbc jars directory 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 jdbc1 specification if you build with a Java2 JDK i e JDK1 2 or JDK1 3 you will build a version that supports the jdbc2 specification 1 http jdbc postgresql org 2 http jakarta apache org ant index html 83 Chapter 8 JDBC Interface Note Do not try to build the driver by calling javac directly as the driver uses some dynamic loading techniques for performance reasons and javac cannot cope Do not try to run ant directly either because some configuration information is communicated through the makefiles Running ant directly without providing these parameters will result in a broken driver 8 1 2 Setting up the Class Pat
66. connection options and their defaults Ipg_exec send a query to the backend lpg_result manipulate the results of a query Ipg_select loop over the result of a SELECT statement Ipg_listen establish a callback for NOTIFY messages lpg_lo_creat create a large object lpg_lo_open open a large object Ipg_lo_close close a large object Ilpg_lo_read read a large object Ipg_lo_write write a large object lpg_lo_lseek seek to a position in a large object Ilpg_lo_tell return the current seek position of a large object Ipg_lo_unlink delete a large object lpg_lo_import import a Unix file into a large object lpg_lo_export export a large object into a Unix file The pg_lo_ routines are interfaces to the large object features of PostgreSQL The functions are designed to mimic the analogous file system functions in the standard Unix file system interface The pg_lo_ routines should be used within a BEGIN COMMIIT transaction block because the file descriptor returned by pg_lo_open is only valid for the current transaction pg_lo_import and pg_lo_export must be used in a BEGIN COMMIT transaction block Example 4 1 shows a small example of how to use the routines Example 4 1 pgtcl Example Program getDBs get the names of all the databases at a given host and port number with the defaults being the localhost and port 5432 return them in alphabetical order proc getDBs host localhost
67. conversion So the computed timestamp 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 datatype 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 23 5 Basic Statements In this section and the following ones we describe all the statement types that are explicitly under stood 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 the statement Thus for example SQL INSERT UPDATE and DELETE com mands may be considered to be statements of PL pgSQL But they are not specifically listed here 23 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 command sent to the main database engine The expression must yield a single value 297 Chapter 23 PL pgSQL SQL Procedural Languag
68. data and save it in a buffer thereby causing a select read ready indication to go away The application can thus use PQconsumeInput to clear the select condition immediately and then examine the results at leisure e PQisBusy Returns 1 if a query is busy that is POget Result would block waiting for input A 0 return indicates that PQgetResult 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 13 Chapter 1 libpq C Library 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 PQflush 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 PQsocket should be used to obtain the backend socket descriptor in preparation for executing select This allows an application using a blocking
69. doubled CREATE FUNCTION double_salary EMP RETURNS integer AS SELECT l salary 2 AS salary LANGUAGE SQL SELECT name double_salary EMP AS dream FROM EMP WHERE EMP cubicle point 2 1 name dream Sam 2400 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 However as we ll see below there are some unfortunate restrictions on how the function may be used This is an example of a function that returns a single EMP row 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 176 Chapter 12 Extending SQL Functions In this case we have specified each of the attributes with a constant value but any computation or expression could have been substituted for these constants Note two important things about defining the function The target list order must be exactly the same as that in which the columns appear in the table associated with the composite type You must typecast the expressions to match the definition of the composite type or you will get error
70. failed connection attempt is signaled by status CONNECTION_BAD Ordinarily an OK status will remain so until POfinish but a communica tions 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 PQconnectPoll with regards to other status codes that might be seen e PQerrorMessage Returns the error message most recently generated by an operation on the connection char PQerrorMessage const PGconn conn Chapter 1 libpg C Library Nearly all libpq functions will set PQerrorMessage if they fail Note that by libpq convention a non empty PQerrorMessage will include a trailing newline PQbackendPID 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 NOTIFY 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 functi
71. 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 public boolean isOpen This returns true if the path is open 103 Chapter 8 JDBC Interface 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 org postgresql util PGobject ta org postgresql geometric PGpoint 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
72. if lobj_fd lt 0 fprintf stderr lobjId can t open large object d n S lo_lseek conn lobj_fd start _ SET buf malloc len 1 nread 0 while len nread gt 0 34 Chapter 2 Large Objects 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 lobjld iat lob j_fd char ADUE int nbytes int nwritten int ples lobj_fd lo_open conn lobjId if lobj_fd lt 0 fprintf stderr can t open lobjId lo_lseek conn lobj_fd start S buf malloc len 1 i lt len i PES i buf buf i for 0 i nwritten 0 while len nwritten gt 0 nbytes lo_write conn lobj nwritten nbytes free buf fprintf stderr n lob j_fd lo_close conn exportFile af void exportFile PGconn conn Oid lobjId int lob j_fd char buf BUFSIZE int nbytes tmp int fd _fd buf nwritten export large object int start int len INV_READ large object d n _ SET len nwritten lobjOid to file out_filename char filename 35 Chapter 2 Large Objects create an inversion object mi lobj_fd lo_open conn lob jId INV_READ if lobj_fd lt
73. in the pg_hba conf file may need to be configured Refer to the Administrator s Guide for details The JDBC Driver supports trust ident password md5 and crypt authentication methods 8 2 Using the Driver 8 2 1 Importing JDBC Any source that uses JDBC needs to import the java sql package using import java sql 84 Chapter 8 JDBC Interface Important Do not import the org postgresql package If you do your source will not compile as javac will get confused 8 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 Class forName method For PostgreSQL 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 ClassNotFoundExcept ion if the driver is not available 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
74. installation layout use the with odbcinst option To be most useful it should be arranged that the driver and the driver manager read the same configuration file Additionally you should install the ODBC catalog extensions That will provide a number of func tions mandated by the ODBC standard that are not supplied by PostgreSQL by default The file usr local pgsql share odbc sqli in the default installation layout contains the appropriate definitions which you can install as follows psql d templatel f LOCATION odbc sql where specifying template1 as the target database will ensure that all subsequent new databases will have these same definitions If for any reason you want to remove these functions again run the file odbc drop sql through psql 7 3 Configuration Files odbc ini contains user specified access information for the psqlODBC driver The file uses conventions typical for Windows Registry files The odbc ini file has three required sections The first is ODBC Data Sources which is a list of arbitrary names and descriptions for each database you wish to access The second required section is the Data Source Specification and there will be one of these sections for each database Each section must be labeled with the name given in ODBC Data Sources and must contain the following entries Driver prefix lib libpsqlodbc so Database DatabaseName Servername localhost Port 5432 Tip Remember that th
75. 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 gt Merge Join 222 Chapter 16 The Rule System gt Seq Scan gt Sort gt Seq Scan on s gt Seq Scan gt Sort gt Seq Scan on shoelace_arrive gt Seq Scan on shoelace_data while omitting the extra range table entry would result in a Merge Join gt Seq Scan gt Sort gt Seq Scan on s gt Seq Scan gt Sort gt 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 Al 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 1
76. it makes the function defini tion unnecessarily 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 180 12 5 2 Base Types in C Language Functions Chapter 12 Extending SQL Functions Table 12 1 gives the C type required for parameters in the C functions that will be loaded into Post greSQL 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 rec ommended 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 12 1 Equivalent C Types for Built In PostgreSQL Types SQL Type C Type Defined In labstime AbsoluteTime utils nabstime h boolean bool postgres h maybe compiler built in box BOX utils geo_decls h bytea bytea postgres h Char char compiler built in character BpChar lpostgres h cid CommandiId lpostgres h date DateADT utils date h smallint int2 int2 or int16 jpostgres h int2vector int2vector ipostgres h integer int4 int4 or int32 postgres h real float4 float4 Ilpostgres h double precision float8
77. it would fail Look at PERFORM for another way to run functions EXECUTE a_output END LANGUAGE plpgsql Example 23 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 23 11 3 In PostgreSQL one 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 CR EAT OR REPI AC PROC ED UR v_url IN VARCHAR v_host OUT v_path OUT VARCHAR l VARCHAR v_query OUT VARCHAR is a_posl IN EG ER a_pos2 IN begin EGER cs_parse_url This will be passed back This one too And this one 315 n C D E END v_host v_path v_query a_pos1 IF a_pos1 RETURN END IF a_pos2 IF a_pos2 v_host v_path RETURN END IF v_hos a_pos1 IF a_pos1 v_path RETURN END IF v_pat v_query N ND now errors NUL NUL NU ins Li Li LL tr v_url 0 THEN r instr v_url 0 THEN te Jibs r substr v_url instr v_url 0 THEN r substr v_url substr v_url REAT F OR REPL AC FUNCTION
78. 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 218 Chapter 16 The Rule System 16 4 3 Cooperation with Views A simple way to protect view relations from the mentioned possibility that someone can try to IN SERT 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 UPDAT DO INSTEAD NOTHING CREATE RULE shoe_del_protect AS ON DELETE TO shoe DO INSTEAD NOTHING O shoe E If Al now tries to do any of these operations on the view relation shoe the rule system will apply the tules 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 Note This way might irritate frontend applications because absolutely nothing happened on the database and thus the backend will not return anything for the query Not even a PGRES_EMPTY_QUERY Will be available in libpq In psql nothing happens This might change in the
79. matter whether they are started inside Q during the execution of Q or after Q is done 21 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 argument 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 sql SPI_connect ret SPI_exec query cnt proc SPI_processed If this is SELECT and some tuple s fetched returns tuples to the caller via elog NOTIC Ri if ret SPI_OK_SELECT amp amp SPI_processed gt 0 za TupleDesc tupdesc SPI_tuptable gt tupdesc SPITupleTable tuptable SPI_tuptable char buf 8192 int i j for j 0 j lt proc j HeapTuple tuple tuptable gt vals j 284 Chapter 21 Server Programming Interface for i 1 buf 0 0 i lt tupdesc gt natts i sprintf buf strlen buf s s SPI_getvalue tuple tupdesc i i tupdesc gt natts
80. 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 NULLs If given it must have exactly the same length as the value list If 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 loop 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 prepare the saved plan on the first 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 S GD plan list 1 2 return Scnt LANGUAGE pltcl 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 t
81. 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 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 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 private 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 224 Chapter 16 The Rule System 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 ar
82. of this discussion but we ll explain how B tree strategies work because you ll need to know that to add a new B tree operator class In the pg_am table the amst rategies column sets the number of strategies defined for this access method For B trees this number is 5 The meanings of these strategies are shown in Table 17 2 Table 17 2 B tree Strategies Operation Index less than 1 less than or equal 2 equal 3 l reater than or equal 4 greater than 5 The idea is that you ll need to add operators corresponding to these strategies to the pg_amop relation see below The access method code can use these strategy numbers regardless of data type to figure out how to partition the B tree compute selectivity and so on Don t worry about the details of adding operators yet just understand that there must be a set of these operators for int 2 int 4 oid and all other data types on which a B tree can operate 17 4 Access Method Support Routines Sometimes strategies aren t enough information for the system to figure out how to use an index Some access methods require additional support routines 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 229 Chapter 17 Interfacing Extensions To Indexes unions and si
83. 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 e 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_eg 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 level 231 Chapter 17 Interfacing Extensions To Indexes 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 the support
84. parses the function s source text and produces an internal binary instruc tion tree the first time the function is called within any one backend process The instruction tree fully translates 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 prepared 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 con ditional code that contains 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 provide a considerable savings of parsing activity 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
85. passed to quote_literal Both take the appropriate 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 v_url ALIAS FOR 3 BEGIN Notice how we scan through the results of a query in a FOR loop using the FOR lt record gt 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 rveferrer_keys key_string THEN RETURN rveferrer_keys referrer_typ Ap Peso END SERS a 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 300 Chapter 23 PL pgSQL SQL Procedural Languag
86. pg_am entry Note Prior to PostgreSQL 7 0 a different scheme was used for registering index specific cost estimation 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 double indexCorrelation The first four parameters are inputs root The query being processed rel The relation the index is on index The index itself 234 Chapter 18 Index Cost Estimation Functions 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 p
87. plan created with SPI_prepare Synopsis SPI_cursor_open name plan 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 nulis 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 the current 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 256 SPI_cursor_open Usage If nulls is NULL then SPI_cursor_open assumes that all parameters if any are NOT NULL 257 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 res
88. 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 pltcldelmod 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 24 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 be different Tcl procedures too This is not normally a concern for a PL Tcl programmer but it might be visible when debugging 329 Chapter 25 PL Perl Perl Procedural Language PL Perl is a loadable procedural language that enables the Perl programming language to be used to write PostgreSQL functions 25 1 Overview Normally PL Perl is installed as a trusted programming language named plperl In this setup certain Perl operations
89. presently no way for them to share global variables either PL Perl cannot currently be used to write trigger functions DBD PgSPI or similar capability should be integrated into the standard PostgreSQL distribution 333 Chapter 26 PL Python Python Procedural Language 26 1 Introduction The PL Python procedural language allows PostgreSQL functions to be written in the Python lan guage 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 from 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 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 26 2 Installation To build PL Python the with python option needs to be specified when running confi
90. result from PQgetResult should be processed using the same PGresult accessor func tions previously described Don t forget to free each result object with PQclear when done with it Note that PQgetResult will block only if a query is active and the necessary response data has not yet been read by POconsumeInput Using PQsendQuery and PQgetResult 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 POgetResult 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 PQconsumeInput If input is available from the backend consume it int PQconsumeInput PGconn conn PQconsumeInput normally returns 1 indicating no error but returns 0 if there was some kind of trouble in which case PQerrorMessage is Set Note that the result does not say whether any input data was actually collected After calling PQconsumeInput the application may check PQisBusy and or PQnotifies to see if their state has changed PQconsumeInput may be called even if the application is not prepared to deal with a result or notification just yet The routine will read available
91. 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 206 Chapter 16 The Rule System 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 those 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 16 3 Views and the Rule System 16 3 1 Implementation of Views in PostgreSQL Views in PostgreSQL are implemented using the rule system In fact there is absolutely no difference between a CREATE VIEW
92. returns an error The arrayVar variable is an array name used in the loop For each tuple ar rayVar 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 tupno The current tuple number starting at zero and incrementing for each iteration of the loop body 53 pg_select 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 54 pg_listen Name pg_listen set or change a callback for asynchronous NOTIFY messages 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 and not empty 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 callbackCommand parameter the request is established or the command string of an already existing request is re
93. root security so it can read write in each user s directory I would hesitate to recommend this however since we have no idea what security holes this creates 7 5 3 Debugging ApplixWare ODBC Connections One good tool for debugging connection problems uses the Unix system utility strace Debugging with strace 1 Start Applix Ware 2 Start an strace on the axnet process For example if 80 Chapter 7 ODBC Interface ps aucx grep ax shows cary 10432 0 0 2 6 1740 392 S Oct 9 0 00 axnet cary 27883 0 9 31 0 12692 4596 S 10 24 0 04 axmain Then run strace f s 1024 p 10432 3 Check the strace output Note from Cary Many of the error messages from ApplixWare go to stderr but lm not sure where stderr is sent so strace is the way to find out For example after getting a Cannot launch gateway on server I ran strace on axnet and got pid 27947 open usr lib libodbc so O_RDONLY 1 ENOENT No such file or di rectory pid 27947 open lib libodbc so O_RDONLY 1 ENOENT No such file or directory pid 27947 write 2 usr2 applix axdata elfodbc can t load library libodbc so n 6 1 EIO I O error So what is happening is that applix elfodbc is searching for libodbc so but it cannot find it That is why axnet cnf needed to be changed 7 5 4 Running the ApplixWare Demo In order to go through the ApplixWare Data Tutorial you need to create the sampl
94. 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 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 Al needs to know for which shoes currently in the store he has the matching shoelaces co
95. sh4 3 brown 40 0 50 0 inch al_bundy gt al_bundy gt INSERT INTO shoelace_data VALUES al_bundy gt felt 6 Bleck p 800p Tem ie al_bundy gt INSERT INTO shoelace_data VALUE al_bundy gt sl2 6 black 100 0 cm al_bundy gt INSERT INTO shoelace_data VALUE al_bundy gt si3 Oy l brack y 3S0 5 nen yy al_bundy gt INSERT INTO shoelace_data VALUE 209 Chapter 16 The Rule System al_bundy gt FSA y 8 black 40 0 7 inen Ayy al_bundy gt INSERT INTO shoelace_data VALUE al_bundy gt SLD 7 45 brown y 2 20e ym al_bundy gt INSERT INTO shoelace_data VALUE al_bundy gt islet 0 brown 0 9 7 im al_bundy gt INSERT INTO shoelace_data VALUE al_bundy gt sl T Sorown 60 gt em 3 al_bundy gt INSERT INTO shoelace_data VALUE al_bundy gt Cog ler a Tyr a brown p Aep VINCE al_bundy gt al_bundy gt 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 sl7 7 brown 60 cm 60 s13 0 black 35 inch 88 9 sl14 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 SELECT FROM shoelace w
96. so no output rows are generated 178 Chapter 12 Extending SQL Functions 12 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 Chap ter 22 for more information The basics of developing a new procedural language are covered in Section 12 7 12 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 compatibil ity an empty body is accepted as meaning that 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 internal function Internal functions are declared in CREATE FUNCTION with language name internal For instance to create an alias for the sqrt fu
97. statement This is in conformance with the JDBC specification which does not require drivers to provide this func tionality 8 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 87 Chapter 8 JDBC Interface a ResultSet instead it returns the number of records affected by the insert update or delete state ment Example 8 2 Simple Delete Example This example will issue a simple delete and print out the number of rows deleted int foovalue 500 PreparedStatement st db prepareStatement DELETE FROM mytable where colum nfoo st setInt 1 foovalue int rowsDeleted st executeUpdate System out printin rowsDeleted rows deleted st close 8 5 Creating and Modifying Database Objects To create modify or drop a database object like a table or view you use the execute method execute is similar to the executeQuery used to issue a select however it doesn t return a result Example 8 3 Drop Table Example This example will drop a table Statement st db createStatement ResultSet rs st executeQuery DROP TABLE mytable st close 8 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 t
98. the in the string RAISE EXCEPTION Inexistent ID gt user_id This will abort the transaction with the given error message 308 Chapter 23 PL pgSQL SQL Procedural Language 23 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 processed 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 im possible 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 execu tion of the function 23 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 OPAQUE Note that the fun
99. 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 compiled language such as C and registered with PostgreSQL as taking no arguments and returning the opaque type a placeholder for unspecified or undefined types This prevents the call handler from being called directly as a function from queries However arguments may be supplied in the actual call to the handler when a function in the language offered by the handler is to be executed 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 CalliInfoData 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 FunctionCallInfo Data Struct if it wishes to return an SQL NULL result The difference between a call handler and an ordinary callee function is that the flinfo gt fn_oid field of the FunctionCallInfoData struct 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 f
100. the libpq C library see Chapter 1 There are several examples of libpq applications in src interfaces libpq examples in the source distribu tion 3 2 Control and Initialization 3 2 1 Environment Variables The following environment variables can be used to set up default values for an environment and to avoid hard coding database names into an application program Note Refer to Section 1 10 for a complete list of available connection options The following environment variables can be used to select default connection parameter values which will be used by PQconnectdb or POset dbLogin if no value is directly specified by the calling code These are useful to avoid hard coding database names into simple application programs Note 1 ibpq uses only environment variables or 1ibpa S POconnectdb conninfo style strings PGHOST sets the default server name If this begins with a slash it specifies Unix domain commu nication 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 38 Chapter 3 libpq C Binding Library PGPASSWORD sets the password used if the backend demands pass
101. the manual is the description of the client side programming interfaces and support li braries for various languages Chapter 1 libpq C Library 1 1 Introduction libpq is the C application programmer s interface to PostgreSQL libpgq 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 libpq C libpgtcl 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 appli cation program can have several backend connections 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 PQset dbLogin Note that these functions will always return a non null object pointer unless perhaps there is too little memory even to allo
102. 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 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 116 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 host 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 environment variables will be used in future connections It returns the previous setting for default host 117 get_defport Name get_defport get default port DV Synopsis get_defport Parameters none Return Type integer or None Default port specification Exceptions S
103. 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 1 contains the function name Column 2 the oid It reads the entire ResultSet loading the values into the function table Important Remember to close the ResultSet after calling this Implementation note about function name look ups PostgreSQL stores the function id s and their corresponding names in the pg_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 returned ResultSet to the addFunctions 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 oid s 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 prevent any unwarranted headaches in the future See Also LargeObjectManager public int getID String name throws SQLException This returns the function id associated by its name If addFunction or addFunctions have not been called for this
104. 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 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 104 public Methods public public public public public public Chapter 8 JDBC Interface PGpoint Required by the driver 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 boolean equals Object obj Parameters obj Object to compare with Returns true if the two points 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 PGpoint in the syntax expected by PostgreSQL Overrides getValue in class PGobject void translate int x int y 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 void translate double x double y Translate
105. therein is executed in a transaction and PostgreSQL rolls back the results if something goes wrong Therefore only one BEGIN statement is allowed 317 Chapter 23 PL pgSQL SQL Procedural Language The exception 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 Q REATE OR REPLACE FUNCTION cs_create_job INTEGER RETURNS INTEGER AS ECLARE v_job_id ALIAS FOR 1 a_running_job_count INTEGER a_num INTEGER PRAGMA AUTONOMOUS_TRANSACTION BEGIN LOCK TABLE cs_jobs IN EXCLUSIVE MODE SELECT count INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NULL iw IF a_running_job_count gt 0 N COMMIT free lock RAISE EXCEPTION Unable to create a new job a job is currently running I E ea J H j DELETE FROM cs_active_job INSERT INTO cs_active_job job_id VALUES v_job_id 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 P fT ELSE RAISE NOTICE Job already running
106. 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_lseek 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_lo_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_tel1 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_lo_lseek Description pg_lo_tel1 returns the current to offset in bytes from the beginning of the large object Usage 62 pg_lo_unlink Name pg_lo_unlink delete a large object Synopsis pg_lo_unlink conn lobjId Inputs conn Specifies a valid database connection
107. variables or failing that using hardwired constants Ky 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 check to see that the backend connection was successfully made HY 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 PQtrace conn debug 22 Chapter 1 libpq C Library start a transaction block res PQexec conn BEGIN if res PQresultStatus res PGRES_COMMAND_OK fprintf stderr BEGIN command failed n PQclear res exit_nicely conn should POQclear PGresult whenever it is no longer needed to avoid memory leaks RY PQclear res fetch rows from the pg_database the system catalog of databases 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
108. when there are many alternatives to be checked 23 6 2 4 IF THEN ELSIF ELSE IF boolean expression THEN statements Tj SIF boolean expression THEN statements ELSIF boolean expression THEN statements 1 302 Chapter 23 PL pgSQL SQL Procedural Language ELSE statements END IF IF THEN ELSIF ELSE provides a more convenient method of checking many alternatives in one statement Formally it is equivalent to nested IF THEN ELSE IF THEN commands but only one END IF is needed Here is an example IF number 0 THE 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 NULL END IF The final ELSE section is optional 23 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 23 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 23 6 3 2 EXIT EXIT label WHEN expression If no label is given the innermost loop is terminated and the
109. 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 available it opens one Once the thread has 111 Chapter 8 JDBC Interface 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 remo
110. 0 Rif include lt stdio h gt include libpq fe h void exit_nicely PGconn conn PQfinish conn exit 1 main char poghost pgport pogoptions pgtty char dbName int nFields int ay j PGconn conn PGresult res 24 Chapter 1 libpq C Library 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 rY 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 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 ay 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 LIST TBL2 if res PQresultStatus res PGRES_COMMAND_OK EJ fprintf stderr LISTEN command failed n PQclear res exit_nicely conn should POclear PG
111. 000 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 gt INSERT INTO shoelace VALUES al_bundy gt s19 0p pink 35 00 7 aneh 0 0 4 al_bundy gt INSERT INTO shoelace VALUES al_bundy gt 7s110 1000 magenta 40 0 inch 0 0 Since this happens often we must lookup for shoelace entries that fit for absolutely no shoe some times We could do that in a complicated statement every 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 gt SELECT FROM shoelace_obsolete sl_name sl_avail sl_color sl_len sl_unit sl_len_cm H sl9 O pink 35 inch 88 9 s110 1000 magenta 40 inch 101 6 For the 1000 magenta shoelaces we must debt 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 223 Chapter 16 The Rule System
112. 1 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 See oe 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 338 Index Symbols libdir 180 odbc ini 77 aggregate functions extending 203 Applix Ware 79 arrays 196 BLOB See large object BSD OS 190 C 38 configure 330 COPY with libpq 16 data types extending 195 Digital UNIX See Tru64 UNIX dynamic_library_path 180 elog 327 332 embedded SQL in C 67 environment variables 19 error message 6 escaping binary strings 9 escaping strings 8 FETCH embedded SQL 71 FreeBSD 190 function 174 internal 179 SQL 174 HP UX 190 input function 195 iODBC 7
113. 1 incr NEW 1 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 328 Chapter 24 PL Tcl Tcl Procedural Language 24 2 6 Modules and the unknown command PL Tcl has support for auto loading Tcl code when used It recognizes a special table pltcl_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 actually contain any initialization script you need it normally de fines a Tcl unknown procedure that is invoked whenever Tcl does not recognize an invoked proce dure 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
114. 2 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 CRE ATE FUNCTION command 1 If the name is an absolute path the given file is loaded 2 If the name starts with the string libdir 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 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 th
115. 24 Chapter 24 PL Tcl Tcl Procedural Language 24 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 procedure 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 internal 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 24 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 Otherwise the command s return value is the number of rows p
116. 25 3 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 25 3 3 Database Access from PL Perl Access to the database itself from your Perl function can be done via an experimental module DBD PgSPT 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 provides only one additional Perl command 2 http www cpan org modules by module DBD APILOS 3 http www cpan org SITES html 332 Chapter 25 PL Perl Perl Procedural Language elog level msg Emit a log or error message Possible levels are DEBUG NOTICE and ERROR DEBUG and NOTICE simply emit the given message into the postmaster log and send it to the client too in the case of NOTICE ERROR raises an error condition further execution of the function is abandoned and the current transaction is aborted 25 3 4 Missing Features PL Perl functions cannot call each other directly because they are anonymous subroutines inside Perl There s
117. 301 23 0 23 IF THEN ELSE IF pioen oreinen isni aio 302 23 6 2 4 IF THEN ELSIF ELSE sesessesesseseeeeseeeesrersreerrreserresereesreseresseeess 302 23 6 3 SIMPlEOOPS ses ere rosno eaae a EE a a EES aa SEERE SER 303 23363 LOOP a oe ARS AA ow a a A 303 23 6 3 25 EXD a R E A E EE A E EEE 303 2303 a WHILE a Be a A E SS 304 23 6 3 4 FOR integer for lo0p esessesessesssresssresrerereersreserrrsreersresereeseeee 304 23 6 4 Looping Through Query Results 2 eee ceecesceseeeeeeeseseessecseeneensees 305 2357 CULSOTS 5 Saree siesve bates a e shay Wass E A E E Sune nda tabectdepreeyeesn 306 23 7 1 Declaring Cursor Variables 0 0 c eee eeceeesesceeseceeceeceseeeeeeeeeseesaesaeeneensees 306 23 72 OPSmIng CULSOTS peere esyeescpeessscesdeecostesdeebesoupsucevderapeusstevesyeeesee eae 306 23 7 2 1 OPEN FOR SELECT r nnp E E E sees 306 23 1 2 2 OPEN FOR EXECU TE ea veesceisesceusdttaee on E mule ice veecs 307 23 7 2 3 OPENing a bound CUTSOT esssseseesseeesseeeseeeseeersresrrresreresrererresenees 307 23 1 3 USING CULSOLS sne eare ee n a a asee aa o eaan AS nenS 307 23T k FETCH tone cra E N R iat eee eee 308 23I A CLOSE o a E A E E E E 308 23 8 Errors and Messages hinon e a R A T NS ETRS 308 23 851 EXCEPHONDS eei Eee ereer eaa enen E EE E EEE SESE SHERE SEE 308 23 9 Trigger Procedures eo sate seen a he N EAS aei 309 23 10 Examples enres ee e oeae a aee ae E Vena Mod corde a e ae E a KE ieS 311 23 11 Porting from
118. 6 IRIX 190 large object 30 libperl 330 libpgtel 45 libpq 1 libpq 38 libpq fe h 6 libpq int h 6 21 Linux 190 NetBSD 191 nonblocking connection 3 12 notice processor 18 NOTIFY 15 55 ODBC 76 odbc sql 77 OpenBSD 191 Oracle 71 312 output function 195 overloading 192 339 Perl 330 PGDATABASE 19 PGHOST 19 PGPASSWORD 19 PGPORT 19 pgtcl closing 58 connecting 46 48 49 50 51 53 creating 56 delete 63 export 65 import 64 notify 55 opening 57 positioning 61 62 reading 59 writing 60 PGUSER 19 pg_config 21 189 pg_conndefaults 49 pg_connect 46 48 50 51 53 pg_lo_close 58 pg_lo_creat 56 pg_lo_export 65 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 PIC 189 PL Perl 330 PL pgSQL 290 PL Python 334 PL SQL 312 PL Tcl 323 Python 334 range table 206 rules 205 and views 207 Index SETOF 174 See Also function sliced bread See TOAST Solaris 191 SPI allocating space 278 279 280 281 282 283 connecting 246 252 254 262 copying tuple descriptors 274 copying tuples 272 275 cursors 256 258 259 260 261 decoding tuples 264 265 266 267 269 270 271 disconnecting 248 executing 249 modifying tuples 276 SPI_connect 246 SPI_copytuple 272 SPI_copytupledesc 274 SPI_copytupleintoslot 275 SPI_cursor_close 261 SPI_cursor_fetch 259 SPI_cursor_find 25
119. 78 SPI repall OC ee iaa a A R ET A E ON E ATAN 279 SPL pire a ses Mites E E A ee a ee ee 280 SPI POSTIPS neman vucte odes ie E a E A E a E E 281 SPI Treetiptables is eni ean i E eae ao ee aie ihe eae ate 282 SPRstree plans se aecis hve E A A E evens Levcreent E 283 21 4 Visibility of Data Changes eseececeeeeeeeceeseeaececeeceseeeeseeesseesaecseesaeenees 284 viii ZS DEN DI EEE EEAS EEEE E Nae I Re 284 TIL Procedural Languages ssssssssssressesersesersessssessssesssscsessesesessesesseseesessssessssessssesessesesessesers 287 22 Procedural Languages scrisoare eein enne E EE r RE eree eao SERS POVEO AE Toka terine iieis 288 22 1 Introduction ceee e ee a ae ae Ea eee a aa e a o n aoas 288 22 2 Installing Procedural Languages sseseseseeseesesressreeserrserrsreersresrrrrsreresrenesesenens 288 23 PL pgSQL SQL Procedural Language 0 eee eee cece csseesecneceeceeeeeseneeseesaecseeneeenees 290 23 Vs OVORVICW tarsi on sistes da Beth E rE E E cheb E EEE ETE det ered age 290 23 1 1 Advantages of Using PL pgSQL oo eee cece ceecesceseeeereeeeseeeecseeneensees 291 23 1 1 1 Better Performance eee ceseesecneceeeeseeeesesseseeaecnecnsensees 291 23 1 2 SQL SUpport 3s se0sc sesselisesveseees Eeer EE a E EE SEEE 291 231 3 Portability sisir a o E KE aie ed E ED ates 291 23 1 2 Developing in PL pgSQL c s s sscssesssessssseesceeecesgesctesess jesssoenisnnceesstessses sees 291 23 2 Structure Of PL PESQL rne Aton
120. 8 SPI_cursor_move 260 SPI_cursor_open 256 SPI_exec 249 SPI_execp 254 SPI_finish 248 SPI_fname 265 SPI_fnumber 264 SPI_freeplan 283 SPI_freetuple 281 SPI_freetuptable 282 SPI_getbinval 267 SPI_getrelname 271 SPI_gettype 269 SPI_gettypeid 270 SPI_getvalue 266 spi_lastoid 326 SPI_modifytuple 276 SPI_palloc 278 SPI_pfree 280 SPI_prepare 252 SPI_repalloc 279 SPI_saveplan 262 SSL 7 340 Tcl 45 323 threads with libpq 20 TOAST 30 and user defined types 196 triggers in PL Tcl 327 Tru64 UNIX 191 unixODBC 76 UnixWare 191 views updating 214 Index 34
121. ARDATA 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 ANGUAGE 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 184 Chapter 12 Extending SQL Functions WITH isStrict CREATE FUNCTION concat_text text text RETURNS text AS PGROOT tutorial funcs LANGUAGE C WITH isStrict Here PGROOT stands 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 strict meaning that the system should automatically assume a NULL result if any input value is NULL By doing this we avoid having to
122. ATE RULE log_shoelace AS ON UPDATE TO shoelace_data WHERE EW sl_avail OLD sl_avail ERT INTO shoelace_log VALUES EW sl_name 0 O H n Ti EW sl_avail current_user current_timestamp Now Al does al_bundy gt UPDATE shoelace_data SET sl_avail 6 al_bundy gt WHERE sl_name s17 and we look at the log table al_bundy gt SELECT FROM shoelace_log sl_name Ssl_avail log_who log_when s17 6 AL 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 216 Chapter 16 The Rule System INSERT INTO shoelace_log VALUES NEW sl_avail current_timestamp shoelace_data NEW shoelace _data OLD NEW sl_name current_user FROM This is a little strange looking 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
123. ATO t ESETRE EE E E E ET 30 2 2 Implementation Features 00 ec ceeeseeseceeceeceseeeeeeseeseecaecsecsaeeseeeceeseseseaecaeesaenaes 30 2 3 IMUELLACES r i eeise eee seats ate eee Sian seein o EEEa Es 30 2 3 1 Creating a Large Object sisenes i etenei seo Soen as sa Eo 31 2 3 2 Importing a Large Object c c sce cisccicsescssstesseetestcsbevssesecescssvedssosnosvtesdosbensees 31 23 3 Exporting a LarseODject sess l aia n a E ARS A EESE 31 2 3 4 Opening an Existing Large Object eee ec eeeeecseceseeeeseceseeeeeeeseneeneenaes 31 2 3 5 Writing Data to a Large Object eee eeceeeeseecse ce ceseeseeeeceeeeseeeeeeneesaeeaes 32 2 3 6 Reading Data from a Large Object eee ees ce cee ceeeseeeeceeceseeeeeeneesaeeaes 32 2 3572 Seeking on a Large Objector a a E E a ai 32 2 3 8 Closing a Large Object Descriptor essseseesssesesssseerrsessrsrssesrrrrererensrersrees 32 23 9 Removing a Large Object ienr oi eu o iiini oneei 32 2 4 Server side Built in Functions ssesesssesesesesrsrestessesrrtserrsreersreneerrereresreserreneeeesee 32 2 5 Accessing Large Objects from Libpq esessseessssssresssrerrsrssrersreersresrrrrsreresreserresrerrsee 33 iii 3 libpqt C Binding Library eee ceeseesse ce cneceseeseeeeceaeeeeecaecsaesaeesecesceeeeeseeeeaaenaes 38 Sid s IMUPOGUCHON EEEE E E dsoceed septs dedesotade beside Mosh cvoceatyuravedpaueveeete EEE E 38 3 2 Control and Initialization cece ese ce cneceseeseeeeceseeeeecaecaaesa
124. D 2 3 8 Closing a Large Object Descriptor A large object may be closed by calling int lo_close PGconn conn int fd where fd is a large object descriptor returned by 1o_open On success 1o_close returns zero On error the return value is negative 2 3 9 Removing a Large Object To remove a large object from the database call Oid lo_unlink PGconn conn Oid lobjId The lobjId argument specifies the OID of the large object to remove 32 Chapter 2 Large Objects 2 4 Server side Built in Functions There are two built in registered functions lo_import and 1o_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 SELECT 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 Libpq libpq fs h and link with the libpq library Example 2 1
125. Description 24 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 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 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 1 gt 2 return 1 323 Chapter 24 PL Tcl Tcl Procedural Language return 2 LANGUAGE pltcl WITH isStrict Note the clause WITH isStrict which saves us from having to think about NULL input val ues 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 argisnu11 For example suppose that we wanted tcl_max with one null and one non null argument to return the non null argument rather than NULL CREATE FUNCTI
126. ERE 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 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 UPDATE and he knows that this result should go into table tl 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
127. ES query optimizer University of California Berkeley Computer Science Department 1 http s2k ftp CS Berkeley EDU 8000 postgres papers 2 http s2k ftp CS Berkeley EDU 8000 postgres papers UCB MS zfong pdf 337 Bibliography Proceedings and Articles Nels Olson Partial indexing in POSTGRES research project University of California UCB Engin T7 49 1993 0676 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 Conference on Management 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 SIGMOD Record 18 3 Sept 1989 M Stonebraker The case for partial indexes SIGMOD Record 18 4 Dec 1989 p 4 1
128. ETE AEREN rS TEON 225 17 Interfacing Extensions To Indexes sipeer oreinen risoria SEAR NE Nes PERNS 228 L721 Introd cton ke e e e E E E E E eb pe eee 228 172 Access Methods iior eeter T E EE E EA E A E 228 17 3 Access Method Strategies eee ei e s E E E e 229 17 4 Access Method Support Routines ssesesesssseeesssseeresrerrrresrrrrsrerrrrsrerrssrsresrnserrsseet 229 VES Operator Classes iscsi isk esient aee eaa eel iae EEEE E aeS 230 17 6 Creating the Operators and Support Routines sssseesssersessresrsssesrssrerrsreserrsseee 230 18 Index Cost Estimation Functions sssseeseseseesseeeressseeersreeterssteresterertssrerrsrnestnseseesesrersseet 234 VEIRA ha Eata S E E E TT RT 237 20 Triggers o a Saou o a a ONE EE E Ea oE ONA EE EAE 239 20 1 Trigger Creation senere iea aTa oe eaea EEE E EEE ES EEn E 239 20 2 Interaction with the Trigger Manager sseeeseeeessseessereseerereereresrrrrsrerrsreeereeseeens 240 20 3 Visibility of Data Changes cs sccsessccassseessssensaveescosetesgesstesnss josssneaicsscvesscesseevsess 242 20 4 Examples eeni n er ar cee eek E E stots E SA EE EOE ease cas ates hades beds 243 21 Server Programming Interfaces sseisepseesei eieiei tre eisses i iri pE e iE 246 QA 31s Interface Functions nin ananira E EE E E E EEE 246 SPlsGonnect ERE E A E RAET A S A EASES 246 SPI AMSA ieee ere ah a nE aaa e Ea a oaa a Eaa on E a SS 248 SPI EXEC A E A AL E E N E a 249 SPI prepares oieri r het in ae
129. FAULT 0 tr VARCHAR TEGER INTEGER gth INTEGER _index gt 0 THEN temp_str substring string FROM beg_index pos IF T iSE T tH vn m position string_to_search IN temp_str pos 0 THEN RETURN 0 RETURN pos beg_index 1 IF ss_length char_length string_to_search len beg WHI END RET END IF LANGUAGE T Written Licens gth char_length string length beg_index ss_length 2 LE beg gt 0 LOOP temp_str substring string FROM beg FOR ss_length pos position string_to_search IN temp_str IF pos gt 0 THEN RETURN beg END IF beg beg 1 LOOP URN 0 t plpgsql by Robert Gaszewski graszew poland com d under the GPL v2 or later Q REATE FUN DECLARE string beg_in CTION instr VARCHAR VARCHAR INTEGER INTEGER RETURNS INTEGER AS ALIAS FOR 1 string_to_search ALIAS FOR 2 dex ALIAS FOR 3 occur_index ALIAS FOR 4 pos in teger NOT NULL DEFAULT 0 occur_number INTEGER NOT NULL DEFAULT 0 temp_s beg I tr VARCHAR TEGER i INTE GER length ss_len BEGIN INTEGER gth INTEGER IF beg_index gt 0 THEN 321 Chapter 23
130. GE option in the Python Setup file These methods are specified by the tag LO Every pgob ject 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 executes a SQL command Synopsis query command 126 query 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 query 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 getresult or dictresult methods or simply printed 127 reset Name reset resets the connection Synopsis reset Parameters none
131. IC is the default no special compiler options are necessary The linker option to produce shared libraries is shared ce c TOOT 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 fpic 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 ce fpi c foo c cc shared o foo so foo o 190 Chapter 12 Extending SQL Functions NetBSD The compiler flag to create PIC is fpic 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 gcc fpic e 00 gcc shared o foo so foo o OpenBSD The compiler flag to create PIC is fpic 1d Bshareable is used to link shared libraries gcc fpie e OOnC ld Bshareable o foo so foo o Solaris The compiler flag to create PIC is KP IC with the Sun compiler and fpic with GCC To link shared libraries the compiler option is G with either compiler or alternatively shared with GCC ce KPIC c foo c cc G o foo so foo o or gcc fpic e foo gcc G o foo so foo o Tru64 UNIX PIC is the default so the compilation command is the usual one Id with special options is used to do the linking c O LOOKS ld shared xpect_unresolved o foo so foo o The same procedure is used with GCC
132. IFY messages was to constantly submit queries even empty ones and then check PQnotifies after each PQexec 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 PQconsumeInput then check PQnotifies You can use select to wait for backend data to arrive thereby using no CPU power unless there is something to do See PQsocket to obtain the file descriptor number to use with select Note that this will work OK whether you submit queries with PQOsendQuery PQgetResult or simply use PQexec You should however remember to check PQnotifies after each PQgetResult 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 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 stri
133. IN IF emprec salary ISNULL THEN RETURN f 311 Chapter 23 PL pgSQL SQL Procedural Language D IF ETURN emprec salary gt sallim ti a END LANGUAGE plpgsql 23 11 Porting from Oracle PL SQL Author Roberto Mello lt rmello fslc usu edu gt This section explains differences between Oracle s 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 23 11 1 Main Differences Some things you should keep in mind when porting from Oracle to PostgreSQL e No default parameters in PostgreSQL e You can overload functions in PostgreSQL This is often used to work around the lack of default parameters Assignments loops and conditionals are similar e 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 23 11 1 1 23 11 1 1 Quote Me on Tha
134. L SELECT clean_EMP 12 2 2 SQL Functions on Base Types The simplest possible SQL function has no arguments and simply returns a base type such as inte ger CREATE FUNCTION one RETURNS integer AS SELECT 1 as RESULT LANGUAGE SQL SELECT one 175 Chapter 12 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 l1 2 AS answer answer 12 2 3 SQL Functions on Composite Types When specifying functions with arguments of composite types we must not only specify which argu ment we want as we did above with 1 and 2 but also the attributes of that argument 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
135. L 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 23 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 integer 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 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 con stant for the duration of the block If NOT NULL is specified an assignment of a NULL value results in a runtime error All variables declared as NOT NULL must have a non NULL default value speci fied 293 Chapter 23 PL pgSQL SQL Procedu
136. L 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 5 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 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 5 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 tryin
137. Large Objects with Libpq Example Program a L 2 z 2 testlo c x test using large objects with libpq Copyright c 1994 Regents of the University of California w 5 gen a m ae include lt stdio h gt include libpgq fe h include libpgq libpq fs h define BUFSIZE 1024 importFile x import file in_filename into database as large object lobjOid sa Oid importFile PGconn conn char filename Oid lobjid int lob j_fd char buf BUFSIZE int nbytes 33 tmp int fd open the file to be read in EJ fd open filename O_RDONLY 0666 if fd lt 0 error fprintf stderr can t open unix Chapter 2 Large Objects Af file s n filename create the large object sy lobjId lo_creat conn INV_READ INV_WRITE if lobjId 0 fprintf stderr can t create large object n lobj_fd lo_open conn lobjId INV_WRITE read in from the Unix file and write to the inversion file ef while nbytes read fd buf BUFSIZE gt 0 tmp lo_write conn lobj_fd buf nbytes if tmp lt nbytes fprintf stderr error while reading large object n void close fd void lo_close conn lobj_fd return lobjlid void pickout PGconn conn Oid lobjId int start int len int lob j_fd char pufy int nbytes int nread lobj_fd lo_open conn lobjId INV_READ
138. ON 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 Sl salary return t if Sl age lt 30 amp amp 100000 0 lt Sl salary return t return f LANGUAGE pltcl There is not currently any support for returning a composite type result value 24 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 return 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 3
139. POLLING_WRITING perform a select for writing on PQsocket conn If you have yet to call POconnectPo11 Le after the call to POQconnect Start behave as if it last returned PGRES_POLLING_WRITING If the select shows that the socket is ready consider it active 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_OK the connection has been successfully made Chapter 1 libpg C Library 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 poll call may of course use that instead At any time during connection the status of the connection may be checked by calling POstatus If this is CONNECTION_BAD then the connection procedure has failed if this is CONNECTION_OK then the connection is ready Either of these states should be equally detectable from the return value of POconnectPo11 as above Other states may be shown during and only during an asyn chronous 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 s
140. POfsize e GetIsNull returns whether a field has the null value bool GetIsNull int tup_num int field_num const Note that Get Value will return the empty string for null fields not the NULL pointer GetIsNull returns whether a field has the null value bool GetIsNull int tup_num const char field_name const Note that Get Value will return the empty string for null fields not the NULL pointer 42 Chapter 3 libpq C Binding Library DisplayTuples prints out all the tuples and optionally the attribute names to the specified output stream void PgDatabase DisplayTuples FILE out 0 bool fillAlign true const char fieldSep bool printHeader true bool quiet false const This function is obsolescent e PrintTuples prints out all the tuples and optionally the attribute names to the specified output stream void PgDatabase PrintTuples FILE out 0 bool printAttName true bool terseOutput false bool fillAlign false const This function is obsolescent 3 5 4 Retrieving Non SELECT Result Information CmdTuples returns the number of rows affected after an INSERT UPDATE or DELETE If the command was anything else it returns 1 int PgDatabase CmdTuples const e OidStatus const char PgDatabase OidStatus const 3 6 Asynchronous Notification PostgreSQL supports asynchronous notification via the LISTEN and NOTIFY commands A back end registers its interest in a particu
141. PostgreSQL 7 2 Programmer s Guide The PostgreSQL Global Development Group PostgreSQL 7 2 Programmer s Guide by The PostgreSQL Global Development Group Copyright 1996 2001 by The PostgreSQL Global Development Group Legal Notice PostgreSQL is Copyright 1996 2001 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 INCIDENTAL 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 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE THE SOFTWARE PRO VIDED HEREUNDER IS ON AN AS IS BASIS AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE SUPPORT UPDATES ENHANCEMENTS OR MODIFICATIONS Table of Conten
142. PostgreSQL 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 PostgreSQL has returned fewer arguments than we have host variables Perhaps you have too many host variables in the INTO var1 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 SELECT command was not unique 204 ECPG_INT_FORMAT Not correctly formatted int type s line d 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 Sd 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 st rtoul for this conversion 206 ECPG_FLOAT_FORMAT Not correctly formatted floating point type s line sd This means the host variable is of type float and the field in the PostgreSQL database is of an other type and contains a value that cannot be interpreted as a float The library uses st rtod f
143. SQL queries using GNU Readline 2 http www informix com 3 http www ibm com 4 http meteora ucsd edu s2k s2k_home html xiii Preface e Anew front end library 1ibpgtc1 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 e A short tutorial introducing regular SQL features as well as those of Postgres95 was distributed with the source code e 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 time We chose a new name PostgreSQL to reflect the relationship between the original POSTGRES and the more recent versions 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 prob lems in the backend code With PostgreSQL the emphasis has shifted to augmenting features and capa
144. SSWORD sets the password used if the backend demands password authentication This is not recommended because the password can be read by others using the ps command with special options on some platforms PGREALM sets the Kerberos realm to use with PostgreSQL if it is different from the local realm If 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 runtime options for the PostgreSQL backend e PGTTY sets the file or tty on which debugging messages from the backend server are displayed The following environment variables can be used to specify user level default behavior for every PostgreSQL session 19 Chapter 1 libpg C Library e PGDATESTY 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 con figuring 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 SQL command for information on correct values for these environment variables 1 11 Threading Behavior libp
145. T S1f p SIE amp x amp y 2 f o 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 if complex NULL return NULL result char palloc 60 sprintf result g g complex gt x complex gt y 195 Chapter 13 Extending SQL Types return result You 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 complex_out before creating the type CREATE FUNCTION complex_in opaque RETURNS complex AS PGROOT tutorial complex LANGUAGE C CREATE FUNCTION complex_out opaque RETURNS opaque AS PGROOT tutorial complex LANGUAGE C Finally we can declare the data type CREATE TYPE complex internallength 16 input complex_in output complex_out As discussed earlier PostgreSQL fully supports arrays of base types Additionally PostgreSQL s
146. The database connection is made using the parameters taken from the string conninfo passed to PQconnectStart This string is in the same format as described above for PQconnect db Neither PQconnect Start nor PQconnectPo11 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 PQconnectPol1l as described below To begin call conn PQconnectStart connection_info_string Ifconnis NULL then libpq has been unable to allocate a new PGconn structure Otherwise a valid PGconn pointer is returned though not yet representing a valid connection to the database On return from PQcon nectStart call status PQstatus conn If status equals CONNECTION_BAD PQconnect Start has failed If PQconnect Start 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 PQconnectPoll last returned PGRES_POLLING_ACTIVE consider it active instead If PQconnectPoll conn last returned PGRES_POLLING_READING perform a select for reading on PQsocket conn Ifit last returned PGRES_
147. UNCTION getname emp RETURNS text AS 177 Chapter 12 Extending SQL Functions SELECT Sl name LANGUAGE SQL SELECT getname new_emp getname None 1 row 12 2 4 SQL Functions Returning Sets As previously mentioned an SQL function may be declared as returning SETOF sometype In this case the function s final SELECT query is executed to completion and each row it outputs is returned as an element of the set Functions returning sets may only be called in the target list of a SELECT 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 An example CREATE FUNCTION listchildren text RETURNS SETOF text AS SELECT name FROM nodes WHERE parent 1 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 Child2 Child3 3 rows SELECT name listchildren name FROM nodes name listchildren Top Childl Top Child2 Top Child3 Childl SubChildl Childl SubChild2 5 rows In the last SELECT notice that no output row appears for Child2 Child3 etc This happens because 1istchildren returns an empty set for those inputs
148. 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 16 6 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 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 mus
149. _OK undeclared first use in this function e 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 pgsql include testprog c 20 Chapter 1 libpg 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 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 testlibpgq 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_co
150. _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 50 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 an empty string 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 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 getTuple tupleNu
151. 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 C EG EG ETIM REATE FUNCTION acs__add_user INTEGER INTEGER VARCHAR DAT E INTEGER INT EG R D ETURNS INTEGER AS ECLARE user_id ALIAS FOR 1 type ALIAS FOR 2 ALIAS FOR 3 creation_user ALIAS FOR 4 creation_ip ALIAS FOR 5 object_ creation_date v_user_id users user_id STYPE v_rel_id membership_rels rel_id sTYPE EGIN v_user_id ETUR v_user_id END LANGUAGE plpgsql 4 http www arsdigita com doc 319 acs_user__new user_id object_type creation_date creation_user creation_ Chapter 23 PL pgSQL SQL Procedural Language 23 11 5 Other Things to Watch For 23 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 23 5 4 Constructs of the type EXECUTE SELECT from 1 will not work unless you use these functions 23 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 f
152. able 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 untrusted procedural language so that only database superusers can create functions in it The writer of a PL TclU 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 24 2
153. ackages If this difficulty arises in your situation a message like this will appear during the build to point out this fact Cannot build PL Perl because libperl is not a shared library You might have to rebuild your Perl installation Refer to x the documentation for details If you see this you will have to re build and install Perl manually to be able to build PL Perl During the configuration process for Perl request a shared library After having reinstalled Perl change to the directory src p1 plper1 in the PostgreSQL source tree and issue the commands gmake clean gmake all gmake install to complete the build and installation of the PL Perl shared library To install PL Perl and or PL PerlU in a particular database use the createlang script for example createlang plperl dbnameorcreatelang plperlu dbname l http www perl com 330 Chapter 25 PL Perl Perl Procedural Language Tip If a language is installed into template all subsequently created databases will have the language installed automatically 25 3 Description 25 3 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 PL PerlU is the same except that the language should be specified as plperlu The body of the function is ordinary Perl code Argu
154. aecaeeaeeas 7 13 1 Main ROUUMES screeds Nn inte E A E E E toe 7 1 3 2 Escaping strings for inclusion in SQL queries eee eee eseeeecseceseeneees 8 1 3 3 Escaping binary strings for inclusion in SQL queries 0 eee eeeeeeeee 9 1 3 4 Retrieving SELECT Result Information eee eeeeeeeseeeeecsecnseeneens 9 1 3 5 Retrieving SELECT Result Values cece eeeceeceecsseeseeeeceeeeseeeeecneesaeeaes 10 1 3 6 Retrieving Non SELECT Result Information 0 00 eee eeeeeee ese eeeeeees 11 1 4 Asynchronous Query Processing cseseccesseceeecereesseceneececeseeceecesueeesaeeeeeeaeeesaeeeee 12 1 5 The Fast Path Interface sisien se r es EE E REEE ES 14 1 6 Asynchronous Notification 0 cee ceesseeseceeceeceseeeeceseescecsecaecsaeeseeeseeseseseaecaeesaenaee 15 1 7 Functions Associated with the COPY Command sssesseseeeesereeesreerseesresrsresesrsseeees 16 1 8 libpq Tracing FUnctioNS s s istisno esine e eaeoe EEEE Sioen 18 1 9 libpq Control FUNCtIONS iissa raea ai Eip eE ansias 18 1 10 Environment Variables occ eee ceesseeseceeceeceseeeeceseeseecaecaeceaeaeeeseeseseseaeeasesaenas 19 1 11 Threading Behavior is i seesscecsscetecgecss cha sesvedssschesstsasaebcshcedstee cesses sisendsssdvcsed sdeetaseaes 20 1 12 Building Libpq Programs cece ceeceeceseeeeceseeseecaecaeceaeseeeseeseaeseaecaeesaeeaes 20 1 13 Example Programs sssini i e r aee o E e E che Westen abe 21 2 Earr Objects nieni oee E E tb E E E eee E eerie 30 Did Tinted C
155. aints triggers e rules e 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 supporting 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 2 A Short History of PostgreSQL The object relational database management system now known as PostgreSQL and briefly called Postgres95 is derived from the POSTGRES package written at the University of California at Berke ley With over a decade of development behind it PostgreSQL is the most advanced open source database available anywhere offering multiversion concurrency control supporting almost all SQL 1 http s2k ftp CS Berkeley EDU 8000 postgres postgres html xii Preface constructs including subselects transactions and user defined types and functions and having a wide range of language bindings 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 presented in The design of POSTGRES and the definition of the initial data model appeared in The POSTGRES data model The design
156. al like introduction to the DB API can be found at http www2 linuxjournal com lj issues issue49 2605 html The pg module defines three objects pgobject which handles the connection and all the requests to the database pglargeob ject which handles all the accesses to PostgreSQL large objects and pgqueryobject 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 I have a link at the bottom to the actual Python code for the page 9 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 1ibpq 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_ SEEK_CUR SEEK_END positional flags used by pglarge seek version version constants that give the current version 1 http www python org topics database DatabaseAPI 2 0 html 113 9 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
157. alary 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 H URNS OPAQUE AS Who works for us when she must pay for IF NEW salary lt 0 THEN RAISE EXCEPTION cannot have a negative salary NEW empname D IF ti Remember who changed the payroll when EW last_date now EW last_user current_user RETURN NEW LANGUAGE plpgsql 310 Chapter 23 PL pgSQL SQL Procedural Language CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp FOR EACH ROW EXECUTE PROCEDURE emp_stamp j 23 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 o
158. alloc allocates memory in upper Executor context Usage TBD 278 SPL_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 279 SPI _pfree Name SP1I_pfree Frees memory in upper Executor context Synopsis SPI_pfree pointer Inputs void pointer Pointer to existing storage Outputs None Description SPI_pfree frees memory in upper Executor context Usage This function is no longer different from plain pfree It s kept just for backward compatibility of existing code 280 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 com patibility of existing code 281 SPI_freetupta
159. ame way as building and installing modules with regular user defined C functions does see Section 12 5 7 2 The handler must be declared with the command CREATE FUNCTION handler_function_name RETURNS OPAQUE AS path to shared object LANGUAGE C The special return type of OPAQUE tells the database that this function does not return one of the defined SQL data types and is not directly usable in SQL statements 3 The PL must be declared with the command 288 Chapter 22 Procedural Languages CREATE TRUSTED PROCEDURAL LANGUAGE language name HANDLER handler_function_name The optional key word TRUSTED tells whether ordinary database users that have no superuser privileges should be allowed to use this language to create functions and trigger procedures Since PL functions 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 TclU 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 locat
160. an 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 10 Architecture 10 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 PostgreSQL uses a simple process per user client server model A PostgreSQL session consists of the following cooperating Unix processes programs e A supervisory daemon process the postmaster the user s frontend application e g the psql program and one or more backend database servers 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 ap plication The library sends user requests over the network to the postmaster Figure 10 1 a which in turn starts a new backend server process Figure 10 1 b 167 Chapter 10 Architecture Figure 10 1 How a connection is established POSTMA STEER client ho st a frontend sends request io postmaster via well known n
161. 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_avail Slcolor Slminlen Slmaxlen slunit FRO WHERE SELECT hoe_data sh unit un sl_name sl_avail 81 6oLor sl_len asl unity ANON nDNA HDA HAHN AANHnA AANA NA HH N 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 WHERE int4ge shoe_ready total_avail 2 h h h h slminlen un un_fact AS h h slmaxlen un un_fact AS h h slunit un un_name rsh slminlen_cm slmaxlen_cm Ssl_len u un_fact AS sl_len_cm shoe_ready It turns out that the planner will collapse this tree into a two level query tree the 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 whi
162. ariable 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 182 Chapter 12 Extending SQL Functions 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 gt data buffer 40 VARHDRSZ is the same as sizeof int 4 but it s considered good style to use the macro VARHDRSZ to refer to the size of the overhead 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 12 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 declared i
163. as interpreted by the parser and produced the parse tree SELECT shoelace sl_name shoelace sl_avail shoelace sl_color shoelace sl_len shoelace sl_unit shoelace sl_len_cm FROM shoelac shoelace 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 rule _RETshoelace with the parse tree SELECT s sl_name s Ssl_color s sl_len float8mul s sl_len FROM shoelace OLD shoelace NEW shoelace_data s unit u WHERE bpchareq s sl_unit s sl_avail s sl_unit u un_fact AS sl_len_cm 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 the 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 FROM SELECT s sl_name Sl_avail shoelace sl_len_cm Slucoldr Ssl_len Sl wnit nnn Hn Ssl_len u un_fact AS sl_len_cm 210 Chapter 16 The Rule System FROM shoelace_data
164. ase EndCopy synchronizes with the backend int PgDatabase EndCopy This function waits until the backend has finished processing the COPY It should either be issued when the last string has been sent to the backend using PgDat abase PutLine or when the last string has been received from the backend using PgDat abase GetLine 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 command The return value is 0 on successful completion nonzero otherwise As an example PgDatabase data data Exec CREATE TABLE foo a int4 b char 16 d double precision ata Exec COPY foo FROM STDIN ata PutLine 3 tHello World t4 5 n ata PutLine 4 tGoodbye World t7 11 n ome o PutLine n data EndCopy o D T 44 Chapter 4 pgtcl Tcl Binding Library 4 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 4 1 gives an overview over the commands available in pgtcl These commands are described further on subsequent pages Table 4 1 pgtc1 Commands Command Description Ipg_connect opens a connection to the backend server Ipg_disconnect closes a connection lpg_conndefaults get
165. at 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 12 5 7 for additional information 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 recompiling it use the LOAD command or begin a fresh session It is recommended to locate shared libraries either relative to 1 ibdir 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
166. ation 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 271 21 3 Memory Management PostgreSQL allocates memory within memory contexts which provide a convenient method of man aging allocations made in many different places that need to live for differing amounts of time De stroying 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_connect 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 memory leakage However if your procedure needs to return an allocated memory object such as a value of a pass by reference datatype you can t allocate the return object using palloc at least not while you are connected 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
167. ays 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 attribute isn t touched So the tule 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 227 Chapter 17 Interfacing Extensions To Indexes 17 1 Introduction The procedures described thus far let you define new types new functions and new operators How ever we cannot yet define a secondary index such as a B tree R tree or hash access method over a new type or its operators Look back at Figure 11 1 The right half shows the catalogs that we must modify in order to tell Po
168. ays be zero for B tree operator classes 230 Chapter 17 Interfacing Extensions To Indexes 17 6 Creating the Operators and Support Routines So now we have an access method and an operator class We still need a set of operators The proce dure for defining operators was discussed in Chapter 14 For the complex_abs_ops operator class on B trees the operators we require are e absolute value less than strategy 1 e absolute value less than or equal strategy 2 e absolute value equal strategy 3 e absolute value greater than or equal strategy 4 e 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 gt y c gt 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 for the rest of the examples The other four opera tors are very similar Refer to complex c or complex source for the details We make the function known to PostgreSQL like this 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
169. basic rules for building C functions are as follows e 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 e When allocating memory use the PostgreSQL routines palloc and pfree instead of the corre sponding C library routines malloc and free The memory allocated by palloc will be freed automatically at the end of each transaction preventing memory leaks e 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 e Most of the internal PostgreSQL types are declared in postgres h while the function manager interfaces PG_FUNCTION_ARGS etc are in fmgr h so you will need to include at least these two files For portability reasons it s best to include postgres h first
170. bilities 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 im plemented Additional SQL92 compliant language features have been added including primary keys quoted identifiers 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 geo metric type support e 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 3 Documentation Resources This manual set is organized into several parts Tutorial An informal introduction for new users User s Guide Documents the SQL query language environment including data types and functions xiv Preface Programmer s Guide Advanced information for application programmers Topics include type and function extensi bility library interfaces and application design issues Administrator s Guide Installation and server management information Reference Manual Reference pages for SQL command syntax a
171. ble 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 282 SPL _freeplan Name SPI_freeplan Releases a previously saved plan Synopsis SPI_freeplan plan Inputs void plan Passed plan Outputs int SPI_LERROR_ARGUMENT if plan is NULL Description SPI_freeplan releases a query plan previously returned by SPI_prepare or saved by SPI_saveplan 283 Chapter 21 Server Programming Interface 21 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
172. ble to revert the driver back to the old 7 1 behavior by setting the compatible 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 Or setBinaryStream methods To use the Large Object functionality you can use either the LargeObject API provided by the PostgreSQL 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 recom mended that you use the LargeObject API if you intend to use Large Objects Example 8 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 column 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 j ps setBinaryStream 2 fis file length ps executeUpdate ps close fis close Here setBina
173. 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 14 3 4 JOIN The JoIN clause if provided names a join selectivity estimation function for the operator note that this is a function name not an operator name JOIN 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 14 3 5 HASHES The HASHES clause if present tells the system that it is OK 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 operato
174. cate the PGconn object The PQstatus 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 con ninfo Unlike PQsetdbLogin below the parameter set can be extended without changing the function signature so use either of this routine or the nonblocking analogues PQconnect Start and PQconnectPo11 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 containing spaces surround it with single quotes e g keyword a value Single quotes and backslashes 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 libpg C Library host Name of host to connect to 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 The default is to connect to a Unix domain socket in tmp hostaddr IP address of host to connect to This shou
175. ccess method is already in the postgres tree src backend access gist Examples at Berkeley come with an overview of the methods and demonstrate spatial index mech anisms for 2D boxes polygons integer intervals and text see also GiST at Berkeley In the box example we are supposed to see a performance gain when using the GiST index it did work for me but I do not have a reasonably large collection of boxes to check that Other examples also worked except polygons I got an error doing test gt CREATE INDEX pix ON polytmp test gt USING GIST p box gist_poly_ops WITH ISLOSSY ERROR cannot open pix PostgreSQL 6 3 Sun Feb 1 14 57 30 EST 1998 I could not get sense of this error message it appears to be something we d rather ask the devel opers about see also Note 4 below What I would suggest here is that someone of you linux guys linux gcc fetch the original sources quoted above and apply my patch see attachment and tell us what you feel about it Looks cool to me but I would not like to hold it up while there are so many competent people around A few notes on the sources 1 I failed to make use of the original HP UX Makefile and rearranged the Makefile from the ancient postgres95 tutorial to do the job I tried to keep it generic but I am a very poor makefile writer just did some monkey work Sorry about that but I guess it is now a little more portable that the original makefile
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177. ch is similar to the one contained in the PostgreSQL distribution It is up to you which one you want to use We plan to coordinate the development of both drivers better in the future To install the ODBC you simply need to supply the enable odbc option to the configure script when you are building the entire PostgreSQL distribution The library will then automatically be built and installed with the rest of the programs If you forget that option or want to build the ODBC driver later you can change into the directory src interfaces odbc and do make and make install there It is also possible to build the driver to be specifically tuned for use with iODBC or unixODBC This means in particular that the driver will use the driver manager s routines to process the config 1 http www iodbc org 2 http www unixodbc org 76 Chapter 7 ODBC Interface uration files which is probably desirable since it creates a more consistent ODBC environment on your system If you want to do that then supply the configure options with iodbc or with unixodbc but not both If you build a stand alone driver not tied to iODBC or unixODBOC then you can specify where the driver should look for the configuration file odbcinst ini By default it will be the directory usr local pgsql etc or equivalent depending on what prefix and or sysconfdir options you supplied to configure To select a specific location outside the PostgreSQL
178. ch we don t want However col lapsing 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 212 Chapter 16 The Rule System 16 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 Everything 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 tl SET b t2 b WH
179. ck 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 Quantity here is 80 292 Chapter 23 PL pgSQL SQL Procedural Language END RAISE NOTICE Quantity here is quantity Quantity here is 50 RETURN quantity END 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 trans action established by an outer query they cannot start or commit transactions since PostgreSQL does not have nested transactions 23 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 pgSQ
180. cok cc reae wen ssod ss Mace ced eats hares Sates 292 23 21 Lexical Details nisreen atasan eiere aep r E E Eer EEE eiS 293 23 3 Declarations sien iea ero ae eke EEEa TEE EE hed co ached egdeb ees 293 23 3 1 Aliases for Function Parameters ssesessseeesseeesesrssteesrererrererrsreereresreerere 294 23 3 2 ROWY PES osr e ea aaae aa O a EEE ESEESE 294 23 3 3 Record Siiner asia E E E E E EE ESES 295 23 34 Attributes ne aeei gainer E R E E Betis 295 2373 5 RENAME DE ETT kdos siesta lecs 296 23 4 EXPLOSSIONS isc o eere ea cee hs shock E EE Eao ESEE ES assoc de Masui chs acts ha ies bees 296 23 52 Basic Statements eseo ii eere aT e er E E EEEE EE E p EEE iE 297 23 51 ASSIBNMEML niii Reasicstiens duce Eere erek A EEEO EEEIEE OEE E EE Er SEE EEEE 297 23 32 SELECT INTO r rear aa E EE e S E S 298 23 5 3 Executing an expression or query with no result sseseseesesseeerseeeeeeeeee 299 23 5 4 Executing dynamic queries piiris E rera 299 23 5 5 Obtaining result Status eee ce isi srecrienr iios eor inss t ivres osre ss itses 301 23 6 Control Structures s 55sscisceisce cascssevesesscessisvesssocseaveessase cosgesstevess sonssseaisasdvassdeesagesses 301 23 6 1 Returning from a FUNCTION ee eect eseeeee cee ceeeeseeeeseeeeseesaecaeseensees 301 236 2 Comdit onal sisser enrian eee r E SE EE Eer ETE er e 301 230 21 IF FTHEN eena hte E E EE r E 301 23 6 2 2 JF THEN ELSE eea scdeass cas cocesaeachesbgedstgs css sa s aa EOS EESTE
181. commercialized it POSTGRES became the primary data manager for the Sequoia 20004 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 im proved performance and maintainability Postgres95 release 1 0 x ran about 30 50 faster on the Wisconsin Benchmark compared to POSTGRES Version 4 2 Apart from bug fixes the following were the major enhancements e 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 e In addition to the monitor program a new program psql was provided for interactive
182. connection to wait for either backend re sponses or other conditions If the result of select indicates that data can be read from the backend socket then PQconsumeInput should be called to read the data after which PQisBusy PQgetResult and or PQnotifies can be used to process the response Nonblocking connections that have used PQsetnonblocking should not use select until PQflush 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 conditions 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 PQsocket When the main loop detects input ready it should call PQconsumeInput to read the input It can then call PQisBusy followed by PQgetResult if PQisBusy returns false 0 It can also call POnotifies 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 O if not If not PQer rorMessage tells why not Successful dispatch is no guarantee that the request will have any effec
183. 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 e Since control is buried inside PQexec it is hard for the frontend to decide it would like to 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 multi ple 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 POQputline 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 behav ior Newer programs can use PQsetnonblocking 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 bu
184. ction 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 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 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 is fired H E telling for which operation the trigger 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 309 Chapter 23 PL pgSQL SQL Procedural Language 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 argumen
185. cursor value is useful to reference an open cursor only until the end of the transaction 23 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 as for 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 23 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 cursl1 23 8 Errors and Messages Use the RAISE statement to report messages and raise errors RAISE level format variable Possible levels are DEBUG write the message into the postmaster log NOTICE write the message into the postmaster log and forward it to the client application and EXCEPTION raise an error aborting the transaction Inside the format string is replaced by the next optional argument s external representation Write to emit a literal Note that the optional arguments must presently be simple variables not expres sions 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
186. d The descriptor specified was not found The statement you are trying to use has not been pre pared 241 line ECPG_INVALID_DESCRIPTOR_INDEX Descriptor index out of range in 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 pre pared 243 ECPG_VAR_NOT_NUMERIC Variable is not a numeric type in line sd The database returned a numeric value and the variable was not numeric 244 100 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 0 ECPG_PGSQL Postgres error s line d Some PostgreSQL error The message contains the error message from the PostgreSQL backend 1 ECPG_TRANS Error in transaction processing line sd PostgreSQL signaled that we cannot start commit or rollback the transaction 2 ECPG_CONNECT Could not connect to database s in line sd The connect to the database did not work ECPG_NOT_FOUND Data not found line sd 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 70 Chapter 6 ecpg Embedded SQL in C 6 4 Limitations What will never be included and why it cannot be done
187. d This string is fed literally to the SQL engine Note in particular that no substitution of PL pgSQL variables is done on the query string The values of variables must be inserted into 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 23 11 for a detailed explanation that will save you some effort 299 Chapter 23 PL pgSQL SQL Procedural Language 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 gquery st ring 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 ph Sele quote_literal newvalue e 7 WHE REE tse oop This example shows use of the functions quote_ident TEXT and quote_literal TEXT Vari ables containing field and table identifiers should be passed to function quote_ident Variables containing literal elements of the dynamic query string should be
188. d gt 0 then you may use the global pointer SPITu pleTable 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 of free vals TupleDesc tupdesc tuple descriptor HeapTuple vals tuples SPITupleTable 250 SPI_exec vals is an array of pointers to tuples the number of useful entries is given by SPI_processed Tu pleDesc tupdesc is a tuple descriptor which you may pass to SPI functions dealing with tuples tupt abcxt alloced and free are internal fields not intended for use by SPI callers Note Functions spi_exec SPI_execp and SPI_prepare change both SPI_processed and SPI_tuptable just the pointer not the contents of the structure Save these two global variables into local procedure variables if you need to access the result of one SPI_exec Or SPI_execp across later calls SPI_finish frees all SPITupleTables allocated during the current procedure You can free a partic ular result table earlier if you are done with it by calling SPI_freetuptable 251 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 t
189. d 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 PQbinaryTuples const PGresult res 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 PQgetvalue const PGresult res int tup_num int field_num For most queries the value returned by POget value is a null terminated character string represen tation of the attribute value But if PObinaryTuples is 1 the value returned by Pogetvalue 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 10 Chapter 1 libpg C Library 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 PQgetisnull Tests a field for a NULL entry Tuple and field indices start at 0 int PQget
190. e 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 gt tg_event rettuple trigdata gt tg_newtuple else rettuple trigdata gt tg_trigtuple check for NULLs if TRIGGER_FIRED_BY_DELETE trigdata gt tg_event amp amp TRIGGER_FIRED_BEFORE trigdata gt tg_event checknull 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 NOTICE 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 243 Chapter 20 Triggers count returns int8 as of PG 7 2 so be careful to convert i int DatumGetInt64 SPI_getbinval SPI_tuptable gt vals 0 SPI_tuptable gt 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
191. e LANGUAGE plpgsql 23 5 5 Obtaining result status 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_OID the Oid of the last row inserted by the most recent SQL query Note that RESULT_OID is only useful after an INSERT query 23 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 23 6 1 Returning from a function RETURN expression The function terminates and the value of expression will be returned to the upper executor The expression s result will be automatically casted into the function s return type as described for assign ments 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 runtime error will occur 23 6 2 Conditionals IF statements let you execute commands based on certain conditions PL pgSQL has four forms of IF IF THEN IF THEN ELSE IF THEN ELSE IF and IF THEN ELSIF THEN ELSE
192. e If the expression s result data type doesn t match the variable s data type or the variable has a specific size precision as for 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 potentially result in runtime 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 23 5 2 SELECT INTO The result of a SELECT command yielding multiple columns but only one row can be assigned to a record variable rowtype 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 runtime error occurs When a record variable is the target it automatically configures itself to the rowtype of the query result columns Except for the INTO clau
193. e Instead they create zero or many new parse trees and can throw away the original one 16 4 2 How These Rules Work Keep the syntax CREATE RULE rule_name AS ON event TO object WHERE rule_qualification 214 Chapter 16 The Rule System 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 e No qualification and not INSTEAD The parse tree from the rule action where the original parse tree s qualification has been added e No qualification but INSTEAD The parse tree from the rule action where the orig
194. e 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 full advantage of this capability PgDatabase GetLine reads a newline terminated line of characters transmitted by the backend server into a buffer st ring of size length int PgDatabase GetLine char string int length Like the Unix system routine fgets this routine copies up to length 1 characters into string Itis like gets however in that it converts the terminating newline into a zero byte PgDatabase GetLine returns EOF at end of file 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 if a new line consists of a backslash followed by a period which indicates that the backend server has finished sending the results of the COPY Therefore if the application ever expects to receive lines that are more than length 1 charac ters long the application must be sure to check the return value of PgDatabase GetLine very carefully PgDatabase PutLine Sends a null terminated st ring to the backend server void PgDatabase PutLine char string The application must explicitly send the characters to indicate to the backend that it has finished sending its data PgDatab
195. e PostgreSQL database name is usually a single word without path names of any sort The PostgreSQL server manages the actual access to the database and you need only specify the name from the client Other entries may be inserted to control the format of the display The third required section is ODBC which must contain the Instal1Dir keyword and which may contain other options Here is an example odbc ini file showing access information for three databases ODBC Data Sources DataEntry Read Write Database QueryOnly Read only Database Test Debugging Database Default Postgres Stripped DataEntry 77 Chapter 7 ODBC Interface ReadOnly 0 Servername localhost Database Sales QueryOnly ReadOnly 1 Servername localhost Database Sales Test Debug 1 CommLog 1 ReadOnly 0 Servername localhost Username tgl Password no way Port 5432 Database test Default Servername localhost Database tgl Driver opt postgres current lib libpsqlodbc so ODBC InstallDir opt applix axdata axshlib 7 4 Windows Applications In the real world differences in drivers and the level of ODBC support lessens the potential of ODBC e Access Delphi and Visual Basic all support ODBC directly Under C such as Visual C you can use the C ODBC API e In Visual C you can use the CRecordSet class which wraps the ODBC API set within an MFC 4 2 class This is the eas
196. e as a public service without warranty and without liability for its behavior or performance However at the time of writing The author of this statement a volunteer on the PostgreSQL support team since November 1996 is not aware of any problems in the PostgreSQL code base related to time transitions around Jan 1 2000 Y2K The author of this statement is not aware of any reports of Y2K problems uncovered in regression testing or in other field use of recent or current versions of PostgreSQL We might have expected to hear about problems if they existed given the installed base and the active participation of users on the support mailing lists XIX Preface e To the best of the author s knowledge the assumptions PostgreSQL makes about dates specified with a two digit year are documented in the current User s Guide in the chapter on data types For two digit years the significant transition year is 1970 not 2000 e g 70 01 01 is interpreted as 1970 01 01 whereas 69 01 01 is interpreted as 2069 01 01 e Any Y2K problems in the underlying OS related to obtaining the current time may propagate into apparent Y2K problems in PostgreSQL Refer to The GNU Project and The Perl Institute for further discussion of Y2K issues particularly as it relates to open source no fee software 8 http www gnu org software year2000 html 9 http language perl com news y2k html XX I Client Interfaces This part of
197. e 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 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 I 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 exe cuted successfully And Al could see the log entries But he cannot create fake entries nor could he manipulate or remove existing ones
198. e 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 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 e Platform information This includes the kernel name and version C library processor memory information 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 facts 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
199. e 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 207 Chapter 16 The Rule System 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 al_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 END UNCTION min integer integer RETURNS integer AS IF 1 lt 2 THEN R ETURN 1 END IF RETURN 2 LANGUAGE plpgsql The real tables we need in the first two rule system descriptions are these CREATE TABLE shoename sh_avail slcolor slminlen slmaxlen slunit T CREATE TABL sl_name sl_avail sl_color sl_len sl_unit CREATE TABLE un_name un_fact shoe_data ehar 10 primary key integer available of pairs char 10 preferred shoelace color float miminum shoelace length float maximum shoelace length char 8 length unit shoelace_data r char 10 primary key integer available of pairs char 10 shoelace colo
200. e 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 187 Chapter 12 Extending SQL Functions 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 iasnull return false return salary gt limit In version 1 coding the above would look like this PG_FUNCTION_INFO_V1 c_overpaid Datum c_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 gt limit GetAttributeByName is the PostgreSQL system function that returns attributes out of the current row It has three arguments the argument of type TupleTableSlot pa
201. e tables that the Tutorial refers to The ELF Macro used to create the tables tries to use a NULL condition on many of the database columns and PostgreSQL does not currently allow this option To get around this problem you can do the following Modifying the ApplixWare Demo 1 Copy opt applix axdata eng Demos sqldemo am to a local directory 2 Edit this local copy of sqldemo am a Search for null_clause NULL b Change this to null_clause Start Applix Macro Editor Open the sqidemo am file from the Macro Editor Select File Compile and Save Exit Macro Editor Start Applix Data P So SOW Oe ee Select Run Macro amp 1 Chapter 7 ODBC Interface 9 Enter the value sqldemo then click OK You should see the progress in the status line of the data window in the lower left corner 10 You should now be able to access the demo tables 7 5 5 Useful Macros You can add information about your database login and password to the standard Applix start up macro file This is an example axhome macros login an file macro login set_set_system_var sql_username tgl set_system_var sql_passwd noSway endmacro Caution You should be careful about the file protections on any file containing user name and password information 82 Chapter 8 JDBC Interface Author Originally written by Peter T Mount lt peter retep org uk gt the original author of the JDBC driver JDBC
202. e 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 23 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 are for use with unbound cursor variables and the other two for use with bound cursor variables 306 Chapter 23 PL pgSQL SQL Procedural Language 23 7 2 1 OPEN FOR SELECT OPEN unbound cursor FOR SELECT The cursor variable is opened and given the specified query to execute The cursor cannot be open al ready 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 SELECTs in PL pgSQL PL pgSQL variable names are substituted for and the query plan is cached for possible re use OPEN cursl FOR SELECT FROM foo WHERE key mykey 23 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
203. easonable implementation of the int 4 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 adver tise 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 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 palloc 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 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 v
204. ed there are two kinds of types in PostgreSQL base types defined in a pro gramming 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 funcs 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 The 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 xy double Vi 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 e When defining your external string representation remember that you must eventually write a complete 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
205. ed as 189 Chapter 12 Extending SQL Functions 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 foo c and we will create a shared library foo 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 BSD OS The compiler flag to create PIC is fpic The linker flag to create shared libraries is shared gcc Epic e foove 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 gee fpi G foose 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 fpic The linker flag for shared libraries is b So CG tZ LOOvc or gcc fpic c foo c and then ld b o foo sl foo o HP UX uses the extension s1 for shared libraries unlike most other systems IRIX P
206. eecsesseceeceeeeseeeeeeeeeseesaecaeeneensees 325 24 2 5 Trigger Procedures in PL T Cl eee cseesseceeceseeseeeeeeeeeseesaecaeeneensees 327 24 2 6 Modules and the unknown command 2 0 eee eee cee ce seeeeeeeeeseeeecneeneensees 328 2427 Teel Procedure NameServer nea Es SS 329 25 PL Perl Perl Procedural Language ssicsiriiiiiiie siririn estera 330 29 A OVERVIEW ienie nalts eee teed oe at ee EE 330 25 2 Building and Installing PL Perl oo eee ceeeseeesecneceeceeeseeeaeeseesaecneeneeesees 330 25 3 Description s eneen ai ates Based A E EEEE E Ee es OTA Maen eda AW Shes 331 25 3 1 PL Perl Functions and Arguments 0 eee ceececeseeeeseeeeseensecneeneensees 331 25 3 2 Data Values in PL Perl cassero t erae e sas oeer E bel SEA EEA 332 25 3 3 Database Access from PL Pet eee ceeseeseceeceeceseeeeeeeeeseesaecaeeeensees 332 25 3 4 Missie Feature Srii ie e peenei n re EEE E S 333 26 PL Python Python Procedural Language eeeeseesesseeeseeseeeessereereseeersrestsrenreresreresenseness 334 26 1 Introduction neen shi enter eE E A E ops E nines E I 334 26 2 Installation essiri teier rae rotet seee k r rere AEE E rap EET Eo densspoasces dbasveens evseey 334 26 3 Usine PL RY thon ieser ree eseo e rees eie eiei EES KONTE ee KEENE EAK SEES tees 334 Bibliography secsissscsssadesceesesasesnsusseasevassessunsneoeasesascgssans cadeeasbeesedensoedsoundsndseaseodonssenescsbansedsestseessedensoenes 337 EEC Te AAP stien sees st
207. eedeheenessee esteshees 91 8 7 1 2 Class org postgres FaStpathecccccsssessssecsscecessecssseessseeess 92 8 7 1 2 1 Methods nicnn ieri hes edi essed 93 8 7 1 3 Class org postgresql fastpath FastpathArg 94 8 7 1 3 1 COmStr Ctr vieiis erone deceissendas sp ritrosi siishi nsei s sirsie oases 95 8 7 2 Geometric Data TYPES sereni ironiese ie eee uota eE EE E 95 873 Laree Objects in ee e a een aes 108 8 7 3 1 Class org postgresql largeobject LargeObject we 108 8 2 3121 Warlables s 3 tense iglesias Gare tite eh hee acess 108 8 7 e3c 12 MethOd Sy csiisisccsss cs cieeaeest ae E E A 108 8 7 3 2 Class org postgresql largeobject LargeObjectManager 110 8 2 3 2 1 Vatlables osc eite ii Ata Ges ake henna ae 110 8 73 22 Method canne e elie inva iets 110 8 8 Using the driver in a multi threaded or a servlet environment eee 111 8 9 Furthet Reading aese scutes oere er an cutee ayer E a s hee tee tees 112 9 PyGreSQL Python Interface nsn r or e e EEE A E E E E 113 Os The pg Module sunnan a a a a a ai NA E 113 Oe Constants 2k hess ae E E A A E 113 9 2 pg Module Functions seise ntete ee ie e NEEE EIEN 113 CONNEC es he I RAE She EE E A 114 pet CEINOS Es ec tseoercis a E A E cual Seweme N E aueeEO 116 E AS Ea d TOTS EEE ET EAEE E AEE EE T TR E ETA eal TE 117 Pet delports ie eee Se a ye Se ee 118 Set defpoft re a e dendebindv i a a tuned stetvedusts 119 PeLdelopt wi Sees Ae a ee ea ei ia es ee Aa 120 SEL ZCELOP U
208. end CONNECTION_AWAITING_RESPONSE Waiting for a response from the server CONNECT ION_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 feedback Connecting Note that if PQconnectStart returns a non NULL pointer you must call Pofinish when you are finished with it in order to dispose of the structure and any associated memory blocks This must be done even if a call to PQconnect Start or PQconnectPoll failed PQconnectPol1 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 Chapter 1 libpg C Library PQconninfoOption PQconndefaults void struct POconninfoOption char
209. enees 84 8 1 3 Preparing the Database for JDBC 00 eee eee eeceeenseeeceeceeeeeeeeeeeneenaes 84 8 2 Usine the Driver is ccfisuencciay seethioutsathne sesh Alois a sitio EEE E a 84 8 2 1 Importing JDBC scsi hts di avec ois ning tht eee ee 84 8 2 2 Loading the Drivers rse eerie Seessschscs ned aeeie ra EEE o EErEE oE ETE re SETE EESE 85 8 2 3 Connecting to the Database sessesessessseesseerseeerrrsreerstesrrresreresresesreseeeeses 85 8 2 4 Closing the Connection sisese eie ii i oE Erai i 86 8 3 Issuing a Query and Processing the Result seseeeeesesesseeereresresrsrrsrrrssrsresrsseeresesene 86 8 3 1 Using the Statement or PreparedStatement Interface eee 87 8 3 2 Using the ResultSet Interface oo ec eeeeeeceeesseeseceeceeeeeeeeeeeneenaes 87 8 4 Performing Updates iis sccc sive cssesssoesessasaseapesestae hone es EE E E EEEE iE 87 8 5 Creating and Modifying Database Objects sesseeesseeesseesreeeseesrsrsserrrsreresrnseerssreees 88 8 6 Storing Binary Data us ssccsifcssseucsscesceesessteccisenstssssosseosees one gptioecessdessssvnssansbeavtesconsdosoes 88 8 7 PostgreSQL Extensions to the JDBC API ou eee eeeee cee csseeseeeeceseeseeeeeeseesaeeaes 91 8 7 1 Accessing the Extensions 0 0 0 0 eceeeeeecseessececeeceseeseeeeceeeeseecsecaecsesseeseesens 91 8 7 1 1 Class org postgresql CONMNECCION veeececessecsssecesseeceeseeeseteeeens 91 SFT VV Methods niii ss csc cicadas pengctesepetsstesdidsteas is sss
210. entation 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 30 Chapter 2 Large Objects The PostgreSQL large object interface is modeled after the Unix file system interface with analogues of open 2 read 2 write 2 1seek 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 dynamicall
211. ependent 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 Another 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 14 3 6 SORT1 and SORT2 The SORT clauses if present tell the system that it is permissible to use the merge join method for a join based on the current operator Both must be specified if either is The current operator must be equality for some pair of data types and the SORT1 and SORT2 clauses name the ordering operator lt operator for the left and right side data types respectively Merge join is based on the idea of sorting the left and righthand tables into order and then scanning them in parallel So both data types must be capable of bein
212. eption Parameters s Definition of the line segment in PostgreSQL s syntax Throws SQLException on conversion failure PGlseg required by the driver void setValue String s throws SQLException Parameters s Definition of the line segment in PostgreSQL s Throws SQLException on conversion failure Overrides setValue in class PGobject 101 public public public Chapter 8 JDBC Interface boolean equals Object obj Parameters obj Object to compare with Returns true if the two line segments 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 PGlseg in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGpath java lang Object org postgresql util PGobject org postgresgql 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 public PGpoint points The points defining this path Constructors public PGpath PGpoint points boolean open Parameters 102 Chapter 8 JDBC Interface points the PGpoints that define the path open True if the path is open
213. ere 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 tule 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 Now we populate unit shoe_data and shoelace_data and Al types the first SELECT in his life al_bundy gt INSERT INTO unit VALUES cm 1 0 TO unit VALUES m 100 0 TO unit VALUES inch 2 54 wn E W H al_bundy gt H al_bundy gt INSER al_bundy gt al_bundy gt INSERT INTO shoe_data VALUES al_bundy gt sHl 2 black po 70 0 90 0 emy al_bundy gt INSERT INTO shoe_data VALUES al_bundy gt C Sn2 Oy Drack y S0 0 40 0 Cineni al_bundy gt INSERT INTO shoe_data VALUES al_bundy gt isha 4 Perown 50 0 6570 en y al_bundy gt INSERT INTO shoe_data VALUES al_bundy gt
214. ery and Processing the Result Any time you want to issue SQL statements to the database you require a Statement or Pre paredStatement 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 8 1 illustrates this process Example 8 1 Processing a Simple Query in JDCB 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 foovalue ResultSet rs st executeQuery 86 Chapter 8 JDBC Interface while rs next System out print Column 1 returned System out println rs getString 1 rs close st close 8 3 1 Using the statement Of PreparedStatement Interface The following must be considered when using the Statement or PreparedStatement interface e You can use a single Statement instance as many times as you want You could create one as s
215. es The statement db DB will open the local database with the name of the user just like pg connect does Name pkey returns 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 139 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 140 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 141 get_tables Name get_tables get list of tables in connected database Synopsis get_tables Parameters none Return Type list List of tables in connected database Description Although you can do this with a simple select it is added here for convenience 142 get_attnames Name get_attnames returns 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 143 get Name get
216. es managed by the POST GRES 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 PostgreSQL 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_largeobject 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 remain ing advantage 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 is planned to equip TOAST with such functionality in the future This section describes the implementation and the programming and query language interfaces to PostgreSQL large object data We use the libpq C library for the examples in this section but most programming 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 de scribed here 2 2 Implementation Features The large object implem
217. esecesseeeeeeseaseaeesaes 38 3 2 1 Environment Varlables ccicaci ttes ennas E a E ia eheviiereamented 38 3 3 libpg Classes nni a hai ain ans Se Ge aA aes 39 3 3 1 Connection Class PgCOnne ction wececsccccssseeesssecsesecesecceeseececesaeecseeeeesteeesans 39 3 3 2 Database Class PgDatabase ecccssssesssssecssseecsssecessecesseeesneeecssaeecseeeseseesenees 39 3 4 Database Connection Functions 0 0 0 eee ceeceseeseeeeceseeeeeeaecasesaeesecesceeeeeeseaseaeenaes 39 3 5 Query Execution FUnCtions 0 ec ee ce erei eet eriei onon EEE EO Ekes E EE EEEE EE Ero 40 3 5 1 Main Routines niieoee eee ee ssdecssechscencdesbessedendssdedsbetuah ivsciscndiapsncaveessnsensces 40 3 5 2 Retrieving SELECT Result Information essesessesseeesseeerseereersresesreseeeeses 41 3 5 3 Retrieving SELECT Result Values 00 0 0 ec eeeeeeeeecseesseeseceeceeeeeeseeeeneenaes 42 3 5 4 Retrieving Non SELECT Result Information 0 eee ec eeeeeeeeereeeees 43 3 6 Asynchronous Notification 0 00 eee eceeeseecsecneceseeseessceseeeeecaecaaesacsaecnsceeeeeeseaseneenaes 43 3 7 Functions Associated with the COPY Command 0 eee eeeseesecesceeeeeeeeeeeeeeaes 43 4 petel Tel Binding Library oseiro inei e EE rE sia ee er iS 45 APT Iptrod cton s eee ee E E eE E E ls te ep E A S 45 4 2 Loading pgtcl into your application 0 0 eee ceceteeeeceeceeeeeeecaecasesaeeaecsceeeeseeees 46 4 3 pgtcl Command Reference Information tect eeeeeceeceseeeeecee
218. essrerererserersrereeesrere 170 11 1 How Extensibility Works stsiscccccisesioscosivthes esd eiheet ews e E A AA 170 11 2 The PostgreSQL Type System eee ce ceseeeseeeecseeseecseceeceseeeseeeeseeseeenesaeenaees 170 11 3 About the PostgreSQL System Catalogs ceessecsecesceseeeeseseeseessecsesneeesees 170 12 Extending SQL Functions 2 0 0 eee eeeeecsecsseeseesecesceseeeeecnecsaesaecnecsceseeeeseaeeseesaecseesensees 174 12 1 Introd ct OM sis 2i5 ss cashes ios ope seeei esa s EE E EEEE E Esai 174 12 2 Query Language SQL Functions 00 0 eeeeeeceesecesceceeeecseceaceceecesaeceaeeeteeeaeeeneees 174 VDs2 Ve EXAM ples EER E Hetvs sn cedswaats E E 174 12 2 2 SQL Functions on Base Types 0 0 eee ecceeesessecseceeceseeeeeeeeeseeseesseeneensees 175 12 2 3 SQL Functions on Composite Types ccc eee ceceseeeeeeeeeeeseeceeneensees 176 12 2 4 SQL Functions Returning Sets 0 eee cee ceeceseeeeeeeeeseeaecseeeensees 178 12 3 Procedural Language Functions 00 eee e ce cceeeeeeceecseesseceeceeceseeeeeeeeseesaecseeeensees 179 12 4 Internal Functions scissione docs coe te onc peben o tends TEE EEEE EEE 179 12 5 C Language FUncti ons ssie ienes E oee rE peia eisers ioi 179 12 5 1 Dynamic Loading ais n e et ien EE K EE E T RE 179 12 5 2 Base Types in C Language Functions e eseeseesereereresrserereresreresrrserees 181 12 5 3 Version 0 Calling Conventions for C Language Functions 00 183 12 5 4 Versi
219. etFastpathAPI where myconn is an open Connection 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 Connection myconn getLargeObjectAPI where myconn is an open Connection 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 PGobject 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 org postgresql Connection myconn addDataType mytype my class name where myconn is an open Connection to PostgreSQL The handling class must extend org postgresql util PGobject 8 7 1 2 Class org postgresql Fastpath public class Fastpath extends Object
220. etails on how to implement your own data type handlers Class org postgresql geometric PGbox 95 Chapter 8 JDBC Interface java lang Object org postgresql util PGobject 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 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 96 Chapter 8 JDBC Interface value a string representation of the value of th object Throws 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 cla
221. etwork socket POSTMASTER SERVER a SERVER ci frontend connected w backend server server ho st And multiple connections can be established di frontend connected to multiple backend servers a SERVER server host 168 Chapter 10 Architecture and connects the frontend process to the new server Figure 10 1 c From that point on the fron tend process and the backend server communicate without intervention by the postmaster Hence the postmaster is always running waiting for connection requests whereas frontend and backend pro cesses come and go The libpg 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 connection 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 Post greSQL superuser Note that the PostgreSQL superuser does not have to be any particular user e g a user named pos
222. ew quote_ident mviews mv_name EXECUTE TRUNCATE TABLE quote_ident mviews mv_name EXECUTE INSERT INTO quote_ident mviews mv_name mviews mv_query 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 lt lt label gt gt FOR record row IN EXECUTE text_expression LOOP statements END LOOP 305 Chapter 23 PL pgSQL SQL Procedural Language This is like the previous form except that the source SELECT statement is specified as a string expres sion which is evaluated and re planned on 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 un intuitive error messages when the true problem is say that one has misspelled the FOR variable name 23 7 Cursors Rather than executing a whole query at once it is possible t
223. executes SQL queries using SPI then these queries may fire triggers again This is known as cascading triggers There is no explicit limitation on the number of cascade levels If a trigger is fired by INSERT and inserts a new tuple in the same relation then this trigger will be fired again Currently there is nothing provided for synchronization etc of these cases but this may change At the moment there is function funny_dup17 in the regress tests which uses some techniques to stop recursion cascading on itself 20 2 Interaction with the 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 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 gt context NULL amp amp IsA fcinfo gt context TriggerData 240 Chapter 20 Triggers If this returns TRUE then it is safe to cast fcinf
224. f FOR creates a loop that iterates over a range of integer values The variable name is automatically 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 304 Chapter 23 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 23 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 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 PERFORM 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 vi
225. f PostgreSQL will be forward compatible For a detailed explanation and examples of how to escape single quotes in different situations please see Section 23 11 1 1 Example 23 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 func tion discussion This function receives an integer and increments it by one returning the incre mented value CREATE FUNCTION add_one integer RETURNS INTEGER AS BEGIN RETURN 1 1 t D LANGUAGE plpgsql Example 23 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 23 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 If the salary field of the EMP table is NULL we return f 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 BEG
226. f 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 109 Chapter 8 JDBC Interface len number of bytes to write 8 7 3 2 Class org postgresql largeobject LargeObjectManager public class LargeObjectManager extends Object java lang Object 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 Connection To get access to this class use the fol lowing segment of code import org postgresql largeobject Connection conn LargeObjectManager lobj code that opens a connection lobj org postgresql Connection myconn getLargeObjectAPI Normally client code would use the BLOB methods 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 LargeObject on how to manipulate the contents of a Large Object
227. f rows processed in an INSERT F or DELETE statement 3 empty 4 empty 5 empty char sqlwarn 8 0 set to W if at least one other is W 1 if W at least one character string X value was truncated when it was stored into a host variable 2 empty 3 empty 4 empty 5 empty 6 empty 7 empty char sqlext 8 sqlca UPDAT E g4 RA af aL Ay ay aes ay af 7 E aes ee If an no error occurred in the last SQL statement sqlca sq1code will be 0 ECPG_NO_ERROR If sqglca sqicode 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 TOW 68 Chapter 6 ecpg Embedded SQL in C 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 sd Should not normally occur This indicates your virtual memory is exhausted 200 ECPG_UNSUPPORTED Unsupported type sS on line sd 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 201 ECPG_TOO_MANY_ARGUMENTS Too many arguments line d This means that
228. false END IF RETURN true END LANGUAGE plpgsql 23 3 5 RENAME RENAME oldname TO newname Using the RENAME declaration you can change the name of a variable record or row This is pri marily 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 2 Fixing this is of low priority since ALIAS covers most of the practical uses of RENAME 23 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 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 has some side effects on the interpretation of constant values In deta
229. float8 lpostgres h interval Interval utils timestamp h lseg LSEG lutils geo_decls h name IName lpostgres 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 lutils date h timestamp Timestamp utils timestamp h tinterval TimeInterval lutils nabstime h varchar VarChar postgres h xid TransactionId postgres h 181 Chapter 12 Extending SQL Functions 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 value fixed length e pass by reference fixed length e 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 r
230. 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 NULLs 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 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 CREATE AGGREGATE avg sfunc float8_accum 203 Chapter 15 Extending SQL Aggregates 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 204 C
231. for info about the available options in the newer syntax Usage 47 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 48 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 49 pg exec Name pg_exec send a command string to the server Synopsis 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
232. ft corner of the data window If you get an error dialog box see the debugging section below 3 The Ready message will appear in the lower left corner of the data window This indicates that you can now enter queries 4 Select a table from Query Choose tables and then select Query Query to access the database The first 50 or so rows from the table should appear 7 5 2 Common Problems The following messages can appear while trying to make an ODBC connection through Applix Data Cannot launch gateway on server elfodbc can t find libodbc so Check your axnet cnf Error from ODBC Gateway IM003 iODBC Driver Manager Specified driver could not be loaded libodbc so cannot find the driver listed in odbc ini Verify the settings Server Broken Pipe The driver process has terminated due to some other problem You might not have an up to date version of the PostgreSQL ODBC package setuid to 256 failed to launch gateway The September release of ApplixWare 4 4 1 the first release with official ODBC support un der Linux shows problems when user names exceed eight 8 characters in length Problem description contributed by Steve Campbell lt scampbell lear com gt Author Contributed by Steve Campbell lt scampbell lear com gt 1998 10 20 The axnet program s security system seems a little suspect axnet does things on behalf of the user and on a true multiuser system it really should be run with
233. function returns whatever the particular access method expects in this case a signed integer The final routine in the file is the support routine mentioned when we discussed the amsupport column of the pg_am table We will use this later on For now ignore it 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 to add entries for these operators to the pg_amop relation To do this we ll need the OIDs of the operators we just defined We ll look up the names of all the operators that take two operands of type complex and pick ours out SELECT o oid AS opoid o oprname INTO TEMP TABLE complex_ops_tmp FROM pg_operator o pg_type t WHERE o oprleft t oid and o oprright t oid and t typname complex opoid oprname 277963 277970 lt 277971 lt 277972 277973 gt 277974 gt 6 rows
234. g 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 xvi Preface 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 e PostgreSQL fails to compile build or install according to the instructions on supported platforms Here program refers to any executable not only the backend server 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
235. g 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 merge join two distinct data types so long as they are logically compatible For example the int 2 versus int 4 equality operator is merge joinable We only need sorting operators that will bring both data types into a logically compatible sequence When specifying merge sort operators the current operator and both referenced operators must re turn boolean the SORT1 operator must have both input data types equal to the current operator s left operand type and the SORT2 operator must have both input data types equal to the current operator s right operand type As with COMMUTATOR and NEGATOR this means that the operator name is suffi cient to specify the operator and the system is able to make dummy operator entries if you happen to define the equality operator before the other ones In practice you should only write SORT clauses for an operator and the two referenced operators should always be named lt Trying to use merge join with operators named anything else will result in hopeless confusion for reasons we ll see in a moment There are additional restrictions on operators that yo
236. g 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 PQoidStatus 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_setauthsve atall Libpgq clients using the crypt encryption method rely on the crypt operating system function which is often not thread safe It is better to use MD5 encryption which is thread safe on all platforms 1 12 Building Libpq Programs To build i e compile and link your libpg programs you need to do all of the following things e Include the 1ibpq fe h header file include lt libpq fe h gt 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 fFoo 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
237. g_who log_when H H s17 6 Al Tue Oct 20 19 14 45 1998 MET DS s13 10 AL Tue Oct 20 19 25 16 1998 MET DS sl6 20 Al Tue Oct 20 19 25 16 1998 MET DS s18 21 Al Tue Oct 20 19 25 16 1998 MET DS 4 rows It s a long way from the one INSERT SELECT to these results And its description will be the last in this document but not the last example First there was the parser s output INSERT FROM INTO shoelace_ok S shoelace_arrive arr_name shoelace_arriv EL ECT shoelace_arrive arr_quant shoelace_arrive shoelace_ok shoelace_ok Now the first rule shoelace_ok_ins is applied and turns it into UPDATE FRO WH ER shoelace SET sl_avail shoelac _arriv int4pl shoelace sl_avail shoelace_arrive arr_quant shoelace_arrive shoelace_o k OLD hoelac shoelace_ok shoelace_ok shoelace_ok NEW shoelace s bpchareq s hoelace 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 FROM WH ER AND shoelace_data SI ET 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 shoelace_arrive shoelace_arrive shoelace_ok shoelace_ok
238. gate 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 34 53 9 In practice 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 sfunc would need to check
239. 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 144 insert Name insert 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 145 update Name update update a database table Synopsis update table a
240. gument 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 result_len If a 4 byte integer result is expected set result_is_int to 1 otherwise set it to 0 Setting result_is_int to 1 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_dint 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 int ptr int integer u PQArgBlock PQfn always returns a valid PGresult The resultStatus 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 back end registers its interest in a particular notification condition with the LISTEN command and can stop listening with the UNLISTEN command All backends listening on a particular condition will be notified asynchronously 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
241. gure If after building and installing you have a file called plpython so possibly a different extension then everything went well Otherwise you should have seen a notice like this flying by Cannot build PL Python because libpython is not a shared library You might have to rebuild your Python installation Refer to x the documentation for details That means you have to rebuild part of your Python installation to supply this shared library The catch is that the Python distribution or the Python maintainers do not provide any direct way to do this The closest thing we can offer you is the information in Python FAQ 3 30 On some operating systems you don t really have to build a shared library but then you will have to convince the PostgreSQL build system of this Consult the Makefile in the src pl plpython directory for details 26 3 Using PL Python There are sample functions in plpython_function sql The Python code you write gets trans formed into a function E g CREATE FUNCTION myfunc text RETURNS text AS return args 0 LANGUAGE plpython l http www python org 2 http www python org doc FAQ html 3 30 334 Chapter 26 PL Python Python Procedural Language 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 ma
242. h To use the driver the jar archive named postgresql jar if you built from source otherwise it will likely be named jdbc7 2 1 1 3jar or jdbc7 2 1 2 jar for the jdbc1 and jdbc2 versions respectively 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 By default the jar archive is installed in the directory usr local pgsql share java You may have it in a different directory if you used the prefix option when you ran configure or if you are using a binary distribution that places it in some different location For instance I have an application that uses the JDBC driver to access a large database containing astronomical objects I have the application and the JDBC driver installed in the usr local lib directory and the Java JDK installed in usr local jdk1 3 1 To run the application I would use export CLASSPATH usr local lib finder jar usr local pgsql share java postgresql jar java Finder finder jar contains the Finder application Loading the driver from within the application is covered in Section 8 2 8 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 inthe postgresql conf file or by supplying the i option flag when starting postmaster Also the client authentication setup
243. hapter 16 The Rule System Author Written by Jan Wieck Updates for 7 1 by Tom Lane 16 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 is 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 16 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
244. he handler for old style dynamically loaded functions 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 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 12 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 that are part of an inheritance hierarchy may have different fields than other members of the same inheritance hierarchy Therefore PostgreSQL provides a procedural interfac
245. he 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 326 Chapter 24 PL Tcl Tcl Procedural Language 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 SE ECT Sval AS ret where the Tcl variable val actually contains doesn t This would result in the final query string SEL ECT doesn t AS ret which would cause a parse error during spi_exec or spi_prepare The submitted query should contain S F which can be formed in PL Tcl as SE le L ECT doesn t AS ret LECT quote Sval AS ret 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 NOTICE ERROR and FATAL DEBUG and NOTICE simply emit the given message into the postmaster log and send it to the client too in the case of NOTICE 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 sh
246. her divided into built in types and user defined types Built in types like int 4 are those that are compiled into the system User defined types are those created by the user in the manner to be described later 170 Chapter 11 Extending SQL An Overview 11 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 incomprehen sible 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 11 1 PostgreSQL System Catalogs Catalog Name Description pg_database databases pg_class tables pg_attribute table columns Ipg_index indexes Ipg_proc procedures functions pg_type data types both base and complex pg_operator operators pg_aggregate aggregate functions pg_am access methods pg_amop access method operators pg_amproc access method support functions pg_opclass access method operator classes 171 Chapter 11 Extending SQL An Overview on ES Figure 11 1 The major PostgreSQL system catalogs attired i at num re yprelid O 1 typinput E t
247. his 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 248 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 count Maximum number of tuples to return Outputs int SPI_LERROR_UNCONNECTED if called from an un connected procedure SPI_LERROR_ARGUMENT if query is NULL or tcount lt 0 SPI_LERROR_UNCONNECTED if procedure is unconnected SPI_LERROR_COPY if COPY TO FROM stdin SPI_LERROR_CURSOR if DECLARE CLOSE CURSOR FETCH SPI_LERROR_TRANSACTION if BEGIN ABORT END SPI_LERROR_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 249 SPI_exec Description SPI_e
248. ia ao ETa aee N e oeeo Raat 203 T6 The Rul System a ea ed E R en ee eo A 205 16 Ty Introduction n a e r E A EE E A E ATN A 205 16 2 What is a Query Tree in i a N E R AR ANE A EOS 205 16 23 The Parts Of a Query Wee eetere pener ae EE TA ENEE EEEE TE EE 205 16 3 Views and the Rule System oo eee cesceeceeeeeeeeseesaecaeceecseeeeeeseaeesaeeaesaeenaee 207 16 3 1 Implementation of Views in PostgreSQL o sees ceseeseeeceeeereeeeeeeensees 207 16 3 2 How SELECT Rules Work 00 eceeescessececeeceseeeeeeeseseesaesnesneensees 207 16 3 3 View Rules in Non SELECT Statements eee eeeeeeeeereeeeecneeenees 212 16 3 4 The Power of Views in PostgreSQL oe eee seecesceseeeeeeeeeseeseesaeesaeesees 213 16 324 1 Benefits oire cesses a E a a E EA A 214 16 3 5 What about updating a view sssesesssesseessseessreererrsresrsresesrrereresresrsresenees 214 16 4 Rules on INSERT UPDATE and DELETE 0 eee eee ceeeneeeeecneeenees 214 16 4 1 Differences from View Rules eee eeesesseceeceeceseeeeseeseseesaecsessaeeaees 214 vii 16 4 2 How These Rules Work ccccccccsesssesssccececececccesesesessesssestsesscesecseecesens 214 16 4 2 1 A First Rule Step by Step oe cee ceceseeeeeeeceseeseeceeeeeaee 216 16 4 3 Cooperation With VieWS cc csesceceeseessesecseesseceececeseeseeeeeeseesaecaesneenaees 219 16 5 Rules atd Permissions cies sickens ee E A a A A 224 16 6 Rules versus Triggers isos ara r r E o eE e E EK
249. id VARDATA t source VARSIZE t VARHDRSZ how many bytes PG_RETURN_TEXT_P new_t PG_FUNCTION_INFO_V1 concat_text Datum 186 Chapter 12 Extending SQL Functions concat_text PG_FUNCTION_ARGS text argl PG_GETARG_TEXT_P 0 text arg2 PG_GETARG_TEXT_P 1 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 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 number 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 concat_text functions shown above are actually wrong in the presence of toasted values because they don t call pg_detoast_datum on their inputs T
250. ience can provide corrections and minor changes in the docu mentation and that is a good way to start The lt pgsql docs postgresql org gt mailing list is the place to get going 5 http www postgresql org 6 http www postgresql org users lounge XV Preface 4 Terminology and Notation The terms PostgreSQL and Postgres will be used interchangeably to refer to the software that accompanies this documentation 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 local 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 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 SQ
251. iest route if you are doing Windows C development under Windows NT 7 4 1 Writing Applications Tf I write an application for PostgreSQL can I write it using ODBC calls to the PostgreSQL server or is that only when another database program like MS SQL Server or Access needs to access the data The ODBC API is the way to go For Visual C coding you can find out more at Microsoft s web site or in your Visual C documentation Visual Basic and the other RAD tools have Recordset objects that use ODBC directly to access data Using the data aware controls you can quickly link to the ODBC back end database very quickly Playing around with MS Access will help you sort this out Try using File Get External Data 78 Chapter 7 ODBC Interface Tip You ll have to set up a DSN first 7 5 ApplixWare Applix Ware has an ODBC database interface supported on at least some platforms Applix Ware 4 4 2 has been demonstrated under Linux with PostgreSQL 7 0 using the psqlIODBC driver contained in the PostgreSQL distribution 7 5 1 Configuration ApplixWare must be configured correctly in order for it to be able to access the PostgreSQL ODBC software drivers Enabling ApplixWare Database Access These instructions are for the 4 4 2 release of ApplixWare on Linux Refer to the Linux Sys Admin on line book for more detailed information 1 You must modify axnet cnf so that elfodbc can find 1ibodbc so the ODBC driver man ager
252. il there is a difference between what these two functions do CREATE FUNCTION logfuncl TEXT RETURNS TIMESTAMP AS DECLARE logtxt ALIAS FOR 1 BEGIN 296 Chapter 23 PL pgSQL SQL Procedural Language u ERT INTO logtable VALUES logtxt now URN now y Ga 4 LANGUAGE plpgsql and CREATE FUNCTION logfunc2 TEXT RETURNS TIMESTAMP AS DECLARE logtxt ALIAS FOR 1 curtime timestamp BEGIN curtime now INSERT INTO logtable VALUES logtxt curtime RETURN curtime END LANGUAGE plpgsql In the case of logfunc1 the PostgreSQL main parser knows when preparing the plan for the IN SERT that the string now should be interpreted as t imest amp because the target field of logtable 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 logfunc1 during the lifetime of the backend Needless to say that this isn t what the programmer wanted In the case of logfunc2 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 assignment to the local variable curt ime the PL pgSQL interpreter casts this string to the timestamp type by calling the text_out and timestamp_in functions for the
253. inal parse tree s qualification has been added e Qualification given and not INSTEAD The parse tree from the rule action where the rule qualification and the original parse tree s qualification have been added e Qualification given and INSTEAD e The parse tree from the rule action where the rule qualification and the original parse tree s qualification 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 rewrite 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 loo
254. 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 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 235 Chapter 18 Index Cost Estimation Functions 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 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 indexSelectivity 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 indexqual
255. ined above for commutator pairs 14 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 behind 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 fortunately 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 neqsel 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
256. instead of the system compiler no special options are required Unix Ware The compiler flag to create PIC is K PIC with the SCO compiler and fpic with GCC To link shared libraries the compiler option is G with the SCO compiler and shared with GCC CS K PIC e 06 cc G o foo so foo o or gcc fpic c foo c gcc shared o foo so foo o 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 1 http www gnu org software libtool 191 Chapter 12 Extending SQL Functions 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 12 5 1 about where the server expects to find the shared library files 12 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
257. ion 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 22 1 Manual Installation of PL pgSQL The following command tells the database server where to find the shared object for the PL pgSQL language s call handler function CREATE FUNCTION plpgsql_call_handler RETURNS OPAQUE AS Slibdir plpgsql LANGUAGE C The command CREATE TRUSTED PROCEDURAL LANGUAGE plpgsql HANDLER plpgsqli_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 289 Chapter 23 PL pgSQL SQL 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 23 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 e 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 e is easy to use The PL pgSQL call handler
258. 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 8 1 Setting up the JDBC Driver 8 1 1 Getting the Driver Precompiled versions of the driver can be downloaded from the PostgreSQL JDBC web site Alternatively you can build the driver from source Although you should only need to do this if you are making changes to the source code Starting with PostgreSQL version 7 1 the JDBC driver is built using Ant a special tool for building Java based packages You should download Ant from the Ant web site and install it before proceed ing Precompiled Ant distributions are typically set up to read a file ant rc in the current user s home directory for configuration For example to use a different JDK than the default this may work JAVA_HOME usr local sun jdk1 3 JAVACMD JAVA_HOME bin java To build the driver add the with java option to your
259. isnull const PGresult res 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 PQgetvalue will return an empty string not a null pointer for a NULL field PQgetlength Returns the length of a field attribute value in bytes Tuple and field indices start at 0 int PQgetlength 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 PQgetvalue Note that for character represented values this size has little to do with the binary size reported by POfsize e 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 pgbool 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 xfieldName null terminated array of replacement field names PQOprintOpt This function was formerly used by psql to print query results but this is no longer the case and this functio
260. ject 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 function The mode value can be obtained by OR ing the constants defined in the pg module INV_READ INV_WRITE 156 close Name close closes 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 same way than the UNIX close function 157 read Name read reads 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 158 write Name write writes 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 inva
261. ket 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 134 endcopy Name endcopy synchronizes 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 135 locreate Name locreate creates of large object in the database LO Synopsis locreate mode Parameters mode Large object create mode Return Type pglarge Object handling the 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 136 getlo Name get lo builds 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
262. keyword The keyword of the option char envvar Fallback environment variable name char compiled Fallback compiled in default value char val Option s current value or NULL char label Label for field in connect dialog char dispchar Character to display for this field in a connect dialog Values are wy Display entered value as is ey Password field hide value Dp Debug option don t show by default int dispsize Field size in characters for dialog Returns a connection options array This may be used to determine all possible POconnectdb options and their current default values The return value points to an array of PQOconninfoOption structs which ends with an entry having a NULL keyword pointer Note that the default values val fields will depend on environment variables and other context Callers must treat the connection options data as read only After 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 Note that even if the backend connection attempt fail
263. l 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 sROWTYP E notation although one might ex pect a bare table name to work as a type declaration it won t be accepted within PL pgSQL functions 294 Chapter 23 PL pgSQL SQL Procedural Language 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 rowtype variable not OID or other system attributes because the row could be from a view The fields of the rowtype inherit the table s field size or precision for data types such as char n 23 3 3 Records name RECORD Record variables are similar to rowtype 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 runtime error Note that RECORD is not a true datatype only a placeholder Thus for example one cannot declare a function returning RECORD 23 3 4 Attributes Using the
264. lan 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 253 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 nulils 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 plan is NULL or tcount lt 0 SPI_LERROR_PARAM if values is NULL and plan was prepared with some parameters SPI_tuptable initialized as in SPI_exec if successful SPI_processed initialized as in SPI_exec if successful 254 SPI_execp 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 SPI_execp for this plan will be unpredictable 255 SPI_cursor_open Name SPI_cursor_open Sets up a cursor using a
265. lar notification condition with the LISTEN command All back ends that are listening on a particular condition will be notified asynchronously when a NOTIFY of that name is executed by another 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 relation libpqt applications are notified whenever a connected backend has received an asynchronous no tification However the communication from the backend to the frontend is not asynchronous The libpq application must poll the backend to see if there is any pending notification information After the execution of a command a frontend may call PgDatabase Notifies to see if any notification data is currently available from the backend PgDatabase Notifies returns the notification from a list of unhandled notifications from the backend The function returns NULL if there are no pend ing notifications from the backend PgDatabase Notifies behaves like the popping of a stack Once a notification is returned from PgDatabase Notifies it is considered handled and will be removed from the list of notifications PgDatabase Notifies retrieves pending notifications from the server PGnotify PgDatabase Notifies The second sample program gives an example of the use of asynchronous notification 43 Chapter 3 libpq C Binding Library 3 7 Functions Associated with th
266. ld be in standard numbers and dots form as used by the BSD functions inet_aton et al If a nonzero length string is specified TCP IP com munication is used Using hostaddr 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 host addr a host name lookup is forced If host addr is specified without host the value for hostaddr gives the remote 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 connections dbname The database name user User name to connect as password Password to be used if the server demands password authentication 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 connectio
267. le 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 getnotify will always return None 131 inserttable Name inserttable inserts a 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 typecheck the fields according to the table definition it just look whether or not it knows how to handle such types 132 putline Name put line writes 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 133 getline Name get Line gets a line from server soc
268. les in ttest AKRAKAAAKAAA remember what we said about visibility INSERT 167794 1 vac gt SELECT FROM ttest x 1 2 2 vac gt UPDATI rows ttest SET x null WHERE x 2 NO UPDATE 0 vac gt UPDATI ry Da ICE trigf fired before there are 2 tuples in ttest ttest SET x 4 WHERE x 2 NO ICE trigf fired before there are 2 tuples in ttest NO UPDATE 1 Fh h FE ICE trigf fired after there are 2 tuples in ttest vac gt SELECT FROM ttest X A 4 2 vac gt DELET rows T FROM ttest NO E ICE trigf fired befor there are 2 tuples in ttest NO ICE trigf fired after there are 1 tuples in ttest NO ICE trigf fired befor there are 1 tuples in ttest NO ICE trigf fired after there are 0 tuples in ttest AKRAKAAAKAAA remember what we said about visibility vac gt SELECT FROM ttest 245 Chapter 21 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 a
269. libpgtcl 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 4 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 pgtty options optionalBackendArgs 46 Ppg_connect 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 libpq 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 port Number Specifies the IP port number of the backend server for dbName tty pgtty Specifies file or tty for optional debug output from backend options opt ionalBackendArgs Specifies options for the backend server for dbName Outputs dbHandle If successful 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
270. lid object Description write method allows to write data to the large object starting at current position 159 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 position in the large object The whence parameter can be obtained by OR ing the constants defined in the pg module SE EK_SE T SE EK_CUR SE HA END 160 tell Name tell returns 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 tel11 method allows to get the current position in the large object 161 unlink Name unlink deletes the large object Synopsis unlink Parameters none Return Type none Exceptions SyntaxError Too many arguments IOError Object is not closed or unlink error pg e
271. lor 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 gt SELECT FROM shoe_ready WHERE total_avail gt 2 shoename sh_avail sl_name sl_avail total_avail H H shl 2ks TL 5 sh3 4 s17 7 4 2 rows Al is a shoe guru and so he knows that only shoes of type shl would fit shoelace s17 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_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 shoe_ready WHERE int4ge shoe_ready total_avail 2 211 Chapter 16 The Rule System Similarly the rules for shoe
272. ls It keeps a reference to the pgobject used for its creation sending requests though with its parameters Any modification but dereferencing the pgobject 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 associated with the object error the last warning error message of the connection Be careful In multithreaded environments error may be modified by another thread using the same pgobject Remember these object are shared not duplicated you should provide some locking to be able if you want to check this The oid attribute is very interesting because it allow you reuse the oid later creating the pglarge object with a pgobject getlo method call See also Chapter 2 for more information about the PostgreSQL large object interface open Name open opens a large object Synopsis open mode Parameters mode open mode definition integer 155 Return Type none Exceptions TypeError Bad parameter type or too many arguments IOError Already opened ob
273. lso 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 state ments This 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 21 1 Interface Functions SPI_ connect Name SPI_connect Connects your procedure to the SPI manager Synopsis int SPI_connect void Inputs None 246 SPI_connect Outputs int Return status SPI_LOK_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 execu
274. ly 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 11 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 int 4 that are implemented in a language such as C 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 furt
275. mber returns the fields of the indicated tuple in a list Tuple numbers start at zero 51 pg_result 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 for each 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 52 pg_select Name pg_select loop over the result of a SELECT statement Synopsis pg_select dbHandle queryString arrayVar queryProcedure Inputs dbHandle Specifies a valid database handle queryString Specifies a valid SQL select query arrayVar Atray 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 gqueryString must be a SELECT statement Anything else
276. ments 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 S_ 1 LANGUAGE plperl If a NULL 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 WITH isStrict to the function definition to make PostgreSQL do something more reasonable if a NULL 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 NULL CREATE FUNCTION perl_max integer integer RETURNS integer AS my a b _ if defined a if defined b return undef return Sb if defined b return Sa if a gt Sb return Sa return b LANGUAGE plperl As shown above to return a NULL from a PL Perl function return an undefined value This can be done whether the f
277. mmand 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 LANGUAGE C CREATE FUNCTION test int int RETURNS int AS filename test_2arg LANGUAGE C The names of the C functions here reflect one of many possible conventions Prior to PostgreSQL 7 0 this alternative syntax did not exist There is a trick to get around the prob lem 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 192 Chapter 12 Extending SQL Functions 12 7 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
278. mpatible data source This could be anything from a text file to an Oracle or PostgreSQL RDBMS The backend access comes from ODBC drivers or vendor specific drivers that allow data access psqlODBC which is included in the PostgreSQL distribution is such a driver along with others that are available such as the OpenLink ODBC drivers Once you write an ODBC application you should be able to connect to any back end database regardless of the vendor as long as the database schema is the same For example you could have MS SQL Server and PostgreSQL servers that have exactly the same data Using ODBC your Windows application would make exactly the same calls and the back end data source would look the same to the Windows application 7 2 Installation In order to make use of an ODBC driver there must exist a driver manager on the system where the ODBC driver is to be used There are two free ODBC driver managers for Unix like operating systems known to us iODBC and unixODBC Instructions for installing these driver managers are to be found in the respective distribution Software that provides database access through ODBC should provide its own driver manager which may well be one of these two Having said that any driver manager that you can find for your platform should support the PostgreSQL ODBC driver or any other ODBC driver for that matter Note The unixODBC distribution ships with a PostgreSQL ODBC driver of its own whi
279. myview AS SELECT FROM mytab compared against the two commands CREATE TABLE myview same attribute list as for mytab j CREATE RULE _RETmyview 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 16 3 2 How SELECT Rules Work Rules ON SELECT are applied to all queries as the last step even 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 UP DATE and DELETE operations so that th
280. n existing large object call int lo_open PGconn conn Oid lobjId int mode The 1objId 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 31 Chapter 2 Large Objects be opened before it is created 1o_open returns a large object descriptor for later use in 1o_read lo_write lo_lseek lo_tell and lo_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 fd into buf 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 fd to the new location specified by of fset The valid values for whence are SEEK_SET SEEK_CUR and SEEK_EN
281. n 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 PGresult char PQcmdStatus const PGresult res PQcmdTuples Returns the number of rows affected by the SQL command char PQcmdTuples const PGresult res j If the SQL command that generated the PGresult was INSERT UPDATE or DELETE this re turns a string containing the number of rows affected If the command was anything else it returns the empty string Il Chapter 1 libpg C Library PQoidValue Returns the object ID of the inserted row if the SQL 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 SQL 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
282. n 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 palloc sizeof float8 result arg 1 0 return result Point makepoint Point pointx Point pointy Point new_point Point palloc sizeof Point new_point gt x pointx gt x 183 Chapter 12 Extending SQL Functions new_point gt y pointy gt y return new_point By Reference Variable Length text copytext text t VARSIZE is the total size of the struct in bytes Ay text new_t text palloc VARSIZE t VARATT_SIZEP new_t VARSIZE t VARDATA is a pointer to the data region of the struct EN memcpy void VARDATA new_t destination void VARDATA t source VARSIZE t VARHDRSZ how many bytes return new_t 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 V
283. n 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_lo_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_lo_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_lo_read reads 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 object from pg_lo_open buf Specifies a valid string variable to write
284. n to the backend Libpq will then refuse to connect if the server does not support SSL Set to 0 default to negotiate with server 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 struct 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 Chapter 1 libpg C Library const char pgtty const char dbName const char login const char pwd This is the predecessor of PQconnectdb with a fixed number of parameters but the same function ality 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 PQsetdbLogin with null pointers for the login and pwd parameters It is provided primarily for backward compatibility with old programs PQconnect Start PQconnectPoll Make a connection to the database server in a nonblocking manner PGconn PQconnectStart const char conninfo PostgresPollingStatusType PQconnectPoll 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
285. name then an SQLException is thrown 8 7 1 3 Class org postgresql fastpath FastpathArg public class FastpathArg extends Object java lang Object org postgresql fastpath FastpathArg 94 Chapter 8 JDBC Interface 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 8 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 len length of data to include public FastpathArg String s Constructs an argument that consists of a String 8 7 2 Geometric Data Types PostgreSQL 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 d
286. name 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 265 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 SPILERROR_NOATTRIBUTE no output function available SPI_result set to SPILERROR_NOOUTFUNC Description SPI_getvalue returns an external string representation of the value of the specified attribute Usage Attribute numbers are 1 based Algorithm The result is returned as a palloc d string Use pfree to release the string when done with it 266 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 att
287. nction 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 12 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 version 1 calling convention is indicated by writing a PG_FUNCTION_INFO_V1 macro call for the function as illus trated 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 be cause of portability problems and lack of functionality but they are still supported for compatibility reasons 179 Chapter 12 Extending SQL Functions 1
288. nd client and server programs Developer s Guide Information for PostgreSQL developers This is intended for those who are contributing to the PostgreSQL project application development information appears in the Programmer s Guide 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 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 information to make your work or play with PostgreSQL more productive Mailing Lists The 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 exper
289. nds 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 it carries additional information that helps the query planner opti mize queries that use the operator Much of this chapter will be devoted to explaining that additional information 14 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 13 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 left arg 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 exam ple is an optional hint to the query optimizer Further details about commutator and
290. nfig as well pg_config libdir usr local pgsql lib Error messages that point to problems in this area could look like the following testlibpgq o In function main testlibpq o text 0x60 undefined reference to PQsetdbLogin testlibpgq 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 libpq 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 postgresql internal libpq int h so you need to add the appropriate I option to your compiler command line 1 13 Example Programs Example 1 1 libpq Example Program 1 f testlibpq c 21 Chapter 1 libpq C Library Test the C version of libpq the PostgreSQL frontend library include lt stdio h gt include lt libpq fe h gt void exit_nicely PGconn conn PQfinish conn exit 1 main char pghost pgport pgoptions pgtty char dbName int nFields int aii j FILE debug 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
291. ng It is like gets however in that it converts the terminating newline into a zero byte POget Line 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 if a new line consists of the two characters which indicates that the backend server has finished sending the results of the copy command If the 16 Chapter 1 libpg C Library 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 PQgetlineAsync PGconn conn char buffer int bufsize This routine is similar to PQget line 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 POconsumeInput and POgetlineAsync until the end of data signal is detected Unlike PQgetline this routine takes responsibility for detecting end of data On each call POQgetlineAsync will return data if a complete newline te
292. ng as PQresultErrorMessage 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 POQerrorMessage when you want to know the status from the latest operation on the connection PQclear Frees the storage associated with the PGresult Every query result should be freed via PQclear when it is no longer needed void POQclear 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 PQmakeEmpt yPGresult Constructs an empty PGresult object with the 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 errorMessage is copied into the PGresult Note that PQclear should eventually be called on the object just as with a PGresult returned by libpg itself 1 3 2 Escaping st
293. nown 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 In the default mode queries are committed only when exec sql commit is issued Ecpg also supports auto commit of transactions via the t command line option or via the exec sql set autocom mit to on Statement In autocommit mode each query is automatically committed unless it is inside an explicit transaction block This mode can be explicitly turned off using exec sql set autocommit to off 75 Chapter 7 ODBC Interface 7 1 Introduction Note Background information originally by Tim Goeke lt t goeke xpressway com gt ODBC Open Database Connectivity is an abstract API that allows you to write applications that can interoperate with various RDBMS servers ODBC provides a product neutral interface between frontend applications and database servers allowing a user or developer to write applications that are portable between servers from different manufacturers The ODBC API matches up on the backend to an ODBC co
294. ns 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 partic ularly those that have to do with access methods that do not The relationships between pg_am pg_amop pg_amproc pg_operator and pg_opclass are particularly hard to understand and will be described in depth in Chapter 17 after we have discussed basic extensions 173 Chapter 12 Extending SQL Functions 12 1 Introduction As it turns out part of defining a new type is the definition of functions that describe its behavior Consequently while it is possible to define a new function without defining a new type the reverse is not true We therefore describe how to add new functions to PostgreSQL before describing how to add new types PostgreSQL provides four kinds of functions e query language functions functions written in SQL procedural language functions functions written in for example PL Tcl or PL pgSQL e internal functions e C language functions Every kind of function can take a base type a composite type or some combination as arguments parameters 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 section can al
295. ntend that shows the problem Be sure to not have anything in your psqlrc 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 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 xvii Preface 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
296. o 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 src include commands trigger h typedef struct TriggerData NodeTag 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 the function is called You may use the following macros to exam ine tg_event TRIGGER_FIRED_BEFORE 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_STATEMENT event Returns TRUE if trigger fired for STATEMENT level event TRIGGER_FIRED_BY_INSERT event Returns TRUE if trigger fired by INSERT 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 src include utils rel h for details about this structure The most interest things are tg_relation gt rd_att descriptor of the relation tuples and tg_relation gt rd_rel gt relname rela
297. o 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 possibility is that a function can return a reference to a cursor that it has set up allowing the caller to read the rows This provides one way of returning a rowset from a function 23 7 1 Declaring Cursor Variables All access to cursors in PL pgSQL goes through cursor variables which are always of the special datatype 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 declaration syntax which in general is name CURSOR arguments FOR select_query FOR may be replaced by Is for Oracle compatibility arguments 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 datatype refcursor but the first may b
298. oa il 252 SPIOX CCP EESE E den sebestiaetis dos sie cad vsniee A odes rien sebesabeoets 254 SPI cursor opens as a n E eees ad ace E tea tos veoh eee ce ie aaa cote 256 SPE Cursor find se 5 334 a E E ees eee A as 258 SPI c rs r TECH i esses he eck cect chee hawk E Fe oak cv tees ee eed hed scde tees 259 SPICUPSOT MOVE AAEE 2533 ec5e5sce8s ede 2edebn ss oe ase deh cies oie iaees Ads Hoopes hes bets 260 SPL cursor Closerie e dae cucu hae ceceeccuduvasdst buts cuteckieeceecetestandetens 261 SPL SaVe plans seis scvaxs save esac svves E eE EATE EET sa E EEEE 262 21 2 Interface Support Functions oo eee ceeeeeeeecseeseesaeceececeseeseseaeeaeesaecaeeeensees 264 SPL AMUM BER 255 lt 5 55 355003 65 AE EEE ATE E EES 264 SPL iam snd eves ehaetees oe ee eae Meee eee ee ae ee Bere ea ects 265 SPL petvalue ais oa Re eR Ne 266 SPL Petbinval ose E EEEE EEE Mandan sdpendvecuavloustuadecesoe ected beste E 267 SPI Petty pet cace sahara st ie heed avi a ee ee 269 SPL SEtty Pei sees sees Aveeadi n e ier tee Ria ene N E deren E A E ETES 270 SPL PetrelnamMe vis c sees Ba a E A A ET ieh 271 2153 Memiory Management ipenira ere pe ane p To OE AE r E aE 272 SPI Copy tuple s a e n ee a ee Renee eA 272 SPLcOpytpledes ess sgcsccssvesseeitewe sited coset we tie E ewe R NA eae ES 274 SPI_copytupleintoslot eee eene a ae e r e RNT EN E i 275 SPI modifyt plE sereoo ee e eana aeea o eae e aE 276 SPI pallot iie ie a T E RE RE T E ch Show beara tase On 2
299. object sseeeserssrssresresressrssrssresresressrssessresresresses 149 Peresu ee ene E r EE E E E E E EE als 149 CIGHECSUIts x i 82 ed ETE EA a A ET EE rt et aN E A A A 150 DES Ul lo KEE E oe eee 151 fede T O GNR 152 ME AMUN PRALNO EEEE OE AE EE ETE EE E EET EE EEEE EEE 153 NLUPlES ora a A Soe i eed ee a R i tt 154 9 6 Lar fe Object Plar generi neie a ERER E E A NE AN 155 Ca 81I TSE A EA SEENE EE O E ATE AS E E EE ETE ETE 155 e KOT AO PENOLA ETETE EERIE T ENEE EAEE EEEE T ONONE CEE AETI RAEE ENET NO 157 TAG hea ccs EE EEE REE Gh a Bee abla ccna Teneo SEESE EEE EN SE ie ca Sane a E EEE 158 WEE erian Sch Goren kes ist neue Soeeoe adhe Save eee bees Seas ea ck Soes we ee A 159 ed SA A E EA AAE SEESE EEEN EE OSSEE SEEE E A ESSEE 160 HOLD E E E E EE VEEE EE ET CE EEEE EEEN 161 unlink 53 sce ss Siana E ER Shaw Cea vk TEE E E Daas cee E tea eee 162 SVA E tees coders fe oe Doeeoe aoe aaa eRe OL EAE Me Be Pulse Senta eT E AR a RE 163 CX POLb Kieth Meats esos ty aa ea ad Mere sea teste E A N 164 9 7 DB APIInterfa teer ood a des deodeeac obese ea e ENE R eS 165 vi IL Server Programming cccccsccccscvssscasesssscccscesscassessovassesescasessnsedssussssssvasvessessvesunseesscassesevedsos vssseoes 166 TOS ALCHILECIUTE o oo ete Sal SR RR IERE NE RSIS 167 10 1 PostgreSQL Architectural Concepts cee eeeeecseessececeeceseeseeeeeeaeeseeenesseenaees 167 11 Extending SQL An Overview esenerereseeeererertesererererrserrerersreruseererensen
300. of the rule system at that time was described in The design of the POSTGRES 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 op erational in 1987 and was shown at the 1988 ACM SIGMOD Conference Version 1 described in The implementation 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 portability and reliability POSTGRES has been used to implement many different research and production applications These include a financial data analysis system a jet engine performance monitoring package an aster oid 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 Infor mation Technologies later merged into Informix which is now owned by IBM picked up the code and
301. 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 we 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 eqsel on the assumption that they ll usually only match a small fraction of the entries in a table 199 Chapter 14 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
302. oid 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 PQpass 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 PQport Returns the port of the connection char PQport const PGconn conn PQtty 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 asynchronous connection procedure CONNECTION_OK or CONNECTION_BAD A good connection to the database has the status CONNECTION_OK A
303. olve a cursor name returned as text by some other function 258 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 SPI_cursor_fetch fetches some more rows from a cursor This is equivalent to the SQL com mand FETCH 259 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 move 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 SQL com mand MOVE 260 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 reso
304. on Doing this will also automatically include ss1 h from OpenSSL 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 returned 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 1 ibpq application program mers should be careful to maintain the PGresult abstraction Use the accessor functions below to get at the contents of PGresult Avoid directly referencing the fields of the PGresult structure be cause 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 PQresultStatus const PGresult res
305. on on conversion failure PGline required by the driver void setValue String s throws SQLException Parameters s Definition of the line segment in PostgreSQL s 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 lines 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 PGline in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGlseg java lang Object org postgresql util PGobject org postgresql geometric PGlseg 100 Chapter 8 JDBC Interface public class PGlseg extends PGobject implements Serializable Cloneable This implements a lseg line segment consisting of two points Variables public PGpoint point These are the two points Constructors public public public public Methods public syntax PGlseg 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 PGlseg PGpoint pl PGpoint p2 Parameters pl first point p2 second point PGlseg String s throws SQLExc
306. on 1 Calling Conventions for C Language Functions 0 185 12 5 5 Composite Types in C Language Functions 0 ce eeeeeeeesesecsecneeeeees 187 12756 Writing Code isc ijsessccccssse cece iiras chaste anair E eoa STRE EE EEEE aiT 188 12 5 7 Compiling and Linking Dynamically Loaded Functions ssssesssseeeee 189 12 6 Function Overloading sissors niso eena ea E iper E Eees 192 12 7 Procedural Language Handlers eseeseeeesseeeesessreessreresresesrrsresesrssesrrsrsresrnrerrssene 192 13 Extending SQL Types iscsi ssssssdssestscestacgs seeesess Ses ssachssagcteasecasasecogesseevess jensspoaies dvessgessegusees 195 14 Extending SQL Operators siese seere trenen a i cuca svecksedvacvecesssbecs oben eT 197 14 T Introduction ssis nta aa E e E SE E E E E sti 197 14 2 Example n eree oneer ee reou oe eo E S E E EE esd E seh eons E E E 197 14 3 Operator Optimization Information eessseeeeseseeeeereersresrsesresrsrssesrssreresresesrssene 197 T4 3 1 COMMUTATOR erher ones arenie inesi ert eose ot n a E acne whens aess 198 14 32 NEGATOR e aeeai iTe ae eer TTE E EEE EEE EEE 198 143 3 RESTRIC Penin e tities Seiten i neers baad at E ee EEE 199 14 3 4 JOIN soe eatine aan Bea eee ae ee O a ene 200 1433 5 EA STIES a E vote RA EEE A teanedtteasons ide E ene ue eeeeas 200 14 3 6 SORT and SORT 2 00 ees cece ceeeeeeceseeseecaecsecaeeeeseeeaesaeecaesaeeeaeed 201 15 Extending SQE At ote 6 ates nnee eeren e a a e
307. oon 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 e If you need to perform a query while processing a ResultSet you can simply create and use another Statement e If you are using threads and several are using the database you must use a separate Statement for each thread Refer to Section 8 8 if you are thinking of using threads as it covers some important points e When you are done using the Statement or PreparedStatement you should close it 8 3 2 Using the ResultSet Interface The following must be considered when using the ResultSet interface e Before reading any values you must call next This returns true if there is a result but more importantly 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 allow 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
308. oper 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 BEGIN LOCK TABLE cs_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 THEN COMMIT free lock raise_application_error 20000 Unable to create a new job a job is cur rently running END IF DELETE FROM cs_active_job INSERT INTO cs_active_job job_id VALUES v_job_id 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 procedure in particular is interesting because it can teach us some things There is no pragma statement in PostgreSQL IfyoudoaLOck 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 func tions called from
309. or this conversion 207 ECPG_CONVERT_BOOL Unable to convert s to bool on line sd 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 4d PostgreSQL returned PGRES_EMPTY_QUERY probably because the query indeed was empty 209 ECPG_MISSING_INDICATOR NULL value without indicator in line d PostgreSQL returned ECPG_MISSING_INDICATOR because a NULL was returned and no NULL indicator variable was supplied 69 S210 Chapter 6 ecpg Embedded SQL in C ECPG_NO_ARRAY Variable is not an array in line d PostgreSQL returned ECPG_NO_ARRAY because an ordinary variable was used in a place that requires an array 211 sd ECPG_DATA_NOT_ARRAY Data read from backend is not an array in line PostgreSQL returned ECPG_DATA_NOT_ARRAY because the database returned an ordinary vari able 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 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
310. other optimizer hints appear below 197 Chapter 14 Extending SQL Operators 14 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 clauses should be provided whenever appropriate be cause 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 2 understands 14 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 lt 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
311. p There is a compiled in recursion limit of currently 10 iterations If after 10 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 215 Chapter 16 The Rule System 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 16 4 2 1 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 CREATE TABLE shoelace_log sl_name char 10 shoelace changed sl_avail integer new available value log_who text who did it log_when timestamp when CRE
312. placed With no cal 1lbackCommand parameter a prior request is canceled After a pg_listen request is established the specified command string is executed whenever a NO TIFY 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 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_lo_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 Sconn INV_READ INV_WRITE 56 pg_lo_ open Name pg_lo_open open a large object Synopsis pg_lo_open con
313. printf stderr Ss message To use a special notice processor call PQsetNoticeProcessor just after creation of anew 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 processor 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 PGconn s current notice processor pointer is copied into the PGresult for possible use by routines like PQgetvalue 1 10 Environment Variables The following environment variables can be used to select default connection parameter values which will be used by PQconnectdb or POsetdbLogin if no value is directly specified by the calling code These are useful to avoid hard coding database names into simple application programs PGHOST sets the default server name If this begins with a slash it specifies Unix domain com munication 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 e PGDATABAS sets the default PostgreSQL database name PGUSER sets the user name used to connect to the database and for authentication PGPA
314. r float shoelace length char 8 length unit unit char 8 the primary key float factor to transform to cm 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 s FRO WHERE S S S S S S S S S nN D D D VY YP YP nN shoename sh_avail Slcolor Slminlen Slminlen un un_fact AS slminlen_cm Slmaxlen Slmaxlen un un_fact AS slmaxlen_cm slunit hoe_data sh unit un Slunit un un_name 208 Chapter 16 The Rule System CREATE VIEW shoelace AS SELECT s sl_name s sl_avail s sl_color s sl_len s sl unit S sl_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 th
315. r 16 The Rule System query tree are the command type This is a simple value telling which command SELECT INSERT UPDATE DELETE pro duced 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 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
316. r 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 124 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 125 9 3 Connection object pgobject This object 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_LAR
317. r RDBMS Packages sseeesseesesseeeseeeeseersreererrsrrrrsrererreserresrerrsre 71 6 6 For th Developer renerne nie a E A AE E E E E S 71 6 6 1 The Preprocessor ecin a E E A RE A E NERSE 71 6 6 2 A Complete Example korenine re ei esoe Sear Eei 74 6 6 3 The Library sasir e a ae he ah ASE ae R 75 Te ODBC Interface imn e E eevee meise tuvoct E A AE E A E E E 76 PVs IO uch On aena e R E RS 76 Bs Jee NEIN ANOT a DE a ES E EE R EAEE 76 T3 COMMPUTATION PILES ienee r ae an eetas eenaa e o iee a e teess 11 7 4 Windows Applications e sseeseseeesessssesssresesrserrsseersrenrrrenserstentsresrerrsreestenereeseneses 78 TAL Warating A ppl Cations censo E E A ENEA 78 EI Appl yx Ware ee aE RETR Ras A A A A Se es 79 TI F COMM SUrat ON nenese Ee EEEo E A EE EEO EEEE S S EENKEER S 79 7 5 2 Common Problems reien oerte ines ee E E E EE EER RS 80 7 5 3 Debugging ApplixWare ODBC Connections ss sssssessseesresssreresrerrrrereerereee 80 7 5 4 Running the ApplixWare Demo ssseesssseeesrsrssesrssesrssreerrsseersrenrerenreerereee 81 PDD SU SOLU Macros 3 seks foc eare bss teed asec ssscattag sala roion iE siS Eees vesa sngvsgcncaviessdendsees 82 8 JDBC Interface nienn inesi ee eo e rE ceva sean A estes odes ene ea tents 83 8 1 Setting up the JDBC Driver nisinsin n nesini seinien iE 83 8 1 1 Getting th Driver nnns eae easan hatin mau SEE E Eie 83 8 1 2 Setting up the Class Path es ee seecsesseesncencesnveneconenssscesssonsenseesssens
318. r 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 while 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 lob j org postgresql Connection conn getLargeObjectAPI PreparedStatement ps con prepareStatement SELECT imgOID FROM imagesLO WHERE imgname ps setString 1 myimage gif ResultSet rs ps executeQuery if rs null while rs next open the large object for reading int oid rs getInt 1 LargeObject obj lobj open oid LargeObjectManager READ 90 Chapter 8 JDBC Interface read 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
319. r classes supported by a given index access method The same 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 a separate pg_opclass row must appear for each access method The OID of the pg_opclass row is used as a foreign key in other tables to associate specific operators and support routines with the operator class You need to add a row with your operator class name for example complex_abs_ops to pg_opclass INSERT INTO pg_opclass opcamid opcname opcintype opcdefault opckeytype VALUES SELECT oid FROM pg_am WHERE amname btree complex_abs_ops SELECT oid FROM pg_type WHERE typname complex true 0 SELECT oid FROM pg_opclass WHERE opcname complex_abs_ops oid opcamid opcname opcintype opcdefault opckeytype H H ZETT 403 complex_abs_ops 277946 t 0 1 row Note that the OID for your pg_opclass row will be different Don t worry about this though We Il get this number from the system later just like we got the OID of the type here 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 set opcdefault to false instead opckeyt ype is not described here it should alw
320. r entered no homepage return http RETURN http END IF END 23 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 into the query as usual 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 wow PERFORM create_mv cs_session_page_requests_mv SELECT session_id page_id count AS n_hits sum dwell_time AS dwell_time count dwell_time AS dwell_count FRO cs_fact_table ROUP BY session_id page_id Q 23 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 datatypes 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 containing the query to be execute
321. r 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 assuming 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 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 200 Chapter 14 Extending SQL Operators 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 d
322. ral Language The default value is evaluated every time the block is entered So for example assigning now toa 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 23 3 1 Aliases for Function Parameters name ALIAS FOR n Parameters passed to functions are named with the identifiers 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 ECLARE subtotal ALIAS FOR 1 BEGIN return subtotal 0 06 iw LANGUAGE plpgsql E CREATE FUNCTION instr VARCHAR INTEGER RETURNS IN ECLARE v_string ALIAS FOR 1 index ALIAS FOR 2 BEGIN Some computations here iw LANGUAGE plpgsql 23 3 2 Rowtypes name tablename sROWTYPE TEGER AS A variable of a composite type is called a row variable or rowtype 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 individua
323. rams sissies peneireiro r isere senssavaddenschesseensdevass sesstevess senssesnsovsevasesetegesssare 45 8 1 Processing a Simple Query in JDCB oo eee eseecee cee ceseeseeeeceeeeeeeeeecaaesaeaececeeeeeeseaesaeenaes 86 8 2 Simple Delete Example sis scsesscessivey cscueiaug aeantes ee aasasises aseays agersde ETE Ere EEE ys EEEE Eri TE 88 8 3 Drop Table Example an ene a e aE e T n iena dvethevsteatgertded pur sveeuied cesta tv sdhceoers 88 8 4 Binary Data Examples i p a re A A R E ad E AE E E 89 22 1 Manual Installation of PL pgSQU oo eee eeeeecseeeseeeceeceeeeeeeeeecseesaecaecseceaeeseeeeseaeeaeecaesneeeaees 289 23 1 A PL pgSQL Trigger Procedure Example 00 0 0 cseeceesceeseeeeeseescesseceeceeceseseeseneeseesaecsecnsensees 310 23 2 A Simple PL pgSQL Function to Increment an Integer eee ce eeseeeeeeeceseeseeeneeneeeaees 311 23 3 A Simple PL pgSQL Function to Concatenate Text 0 eee ec esesecseceeceseeeeeeeseeeeaeecaeeneenaees 311 23 4 A PL pgSQL Function on Composite Type cc ccecceceseeesseeceseeeecaececeseeseeeesesesaeecaesneenaees 311 23 5 A Simple Funct onenn tenes a e eeri a ene ee eee ange ET aaRS EEE IE TERE EREN 313 23 6 A Function that Creates Another Function seseesssseesesssesssesresreesrssenresenrerrnserrsrenteresrerrses 314 23 7 A Procedure with a lot of String Manipulation and OUT Parameters 00 00 eee eee eeees 315 xi Preface 1 What is PostgreSQL PostgreSQL is an object relational da
324. reSQL 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 23 11 1 1 e The show errors command does not exist in PostgreSQL So let s see how this function would look when ported to PostgreSQL CREATE OR REPLACE FUNCTION cs_fmt_browser_version VARCHAR VARCHAR RETURNS 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 D m END LANGUAGE plpgsql Example 23 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
325. res exit_nicely conn should POQclear PGresult whenever it is no longer needed to avoid memory leaks E7 PQclear res fetch rows from the pg_database the system catalog of databases Kf res PQexec conn DECLARE mycursor BINARY CURSOR FOR SELECT FROM test1 if res PQresultStatus res PGRES_COMMAND_OK 2h Chapter 1 libpq C Library D fprintf stderr ECLARE CURSOR command failed n PQclear res exit_nicely conn PQclear res res if PQexec conn FETCH ALL in mycursor res PQresultStatus fprintf stderr PQclear res exit_nicely conn res PGRES_TUPLES_OK FETCH ALL command didn t return tuples properly n i_fnum PQfnumber res i d_fnum PQfnumber res d p_fnum PQfnumber res p for i 0 i lt 3 itt printf type d d size d d n i POftype res i i POfsize res i for i 0 i lt PQntuples res int ival float dval int plen POLYGON pval we hard wire this to the i 3 fields we know about ival int PQgetvalue res i i_fnum dval float PQgetvalue res i d_fnum plen PQgetlength res i p_fnum plen doesn t include the length field so need to increment by VARHDSZ xf pval POLYGON malloc plen VARHDRSZ pval gt size plen
326. result whenever it is no longer needed to avoid memory leaks x PQclear res while 1 wait a little bit between checks waiting with select would be mor fficient Af sleep 1 collect any asynchronous backend messages PQconsumelInput conn check for asynchronous notify messages while notify PQnotifies conn NULL fprintf stderr 25 Chapter 1 libpq C Library ASYNC NOTIFY of s from backend pid d received n notify gt relname notify gt be_pid free notify close the connection to the database and cleanup PQfinish conn return 0 Example 1 3 libpq Example Program 3 testlibpq3 c Test the C version of Libpgq the PostgreSQL frontend library tests the binary cursor interface populate a database by doing the following 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 test1 values 2 89 05 polygon 4 0 3 0 2 0 1 0 the expected output is tuple 0 got i 4 bytes 1 d 4 bytes 3 567000 p 4 bytes 2 points boundbox hi 3 000000 4 000000 lo 1 000000 2 000000 tuple 1 got i 4 bytes 2 d 4 bytes 89 050003 p 4 bytes 2 points boundbox hi 4 000000 3 000000 lo 2 000000 1 000000 ee include lt stdio h gt
327. ribute s value in internal form as a Datum Usage Attribute numbers are 1 based 267 SPI_getbinval Algorithm Does not allocate new space for the datum In the case of a pass by reference datatype the Datum will be a pointer into the given tuple 268 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 SPL result SPI_LERROR_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 type name Use pfree to release the copy when done with it 269 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 SPL result SPI_LERROR_NOATTRIBUTE Description SPI_gettypeid returns the type OID for the specified attribute Usage Attribute numbers are 1 based 270 SPI_getrelname Name SPI_getrelname Returns the name of the specified relation Synopsis SPI_getrelname rel Inputs Rel
328. ries the value returned by GetValue is a null terminated string representation of the attribute value But if BinaryTuples is true the value returned by Get 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 Get 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 BinaryTuples is not yet implemented e GetLength returns the length of a field column in bytes Tuple and field indices start at 0 int PgDatabase GetLength int tup_num int field_num const This is the actual data length for the particular data value that is the size of the object pointed to by GetValue Note that for character represented values this size has little to do with the binary size reported by POfsize e GetLength returns the length of a field column in bytes Tuple and field indices start at 0 int PgDatabase GetLength int tup_num const char field_name const This is the actual data length for the particular data value that is the size of the object pointed to by GetValue Note that for character represented values this size has little to do with the binary size reported by
329. ries 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 trans action 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 the frontend backend communication to a debugging file stream void PQtrace PGconn conn FILE debug_port PQuntrace Disable tracing started by PQt race void PQuntrace PGconn conn 1 9 libpq Control Functions PQsetNoticeProcessor Control reporting of notice and warning messages generated by libpq typedef void PQnoticeProcessor void arg const char message PQnoticeProcessor PQsetNoticeProcessor PGconn conn PQnoticeProcessor proc void arg 18 Chapter 1 libpg C Library By default libpq prints notice messages from the backend on stderr as well as a few error mes sages 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 PQsetNoti ceProcessor 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 f
330. rings 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 Chapter 1 libpg C Library If you want to include strings that have been received from a source that is not trustworthy for example 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 1ength 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 PQescapeString writes an escaped version of the from 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 PQescapeString returns the number of characters written to to not including the terminating zero byte Behavior is undefined when the to and from strings overlap 1 3 3 Escaping binary strings for inclusion in SQL queries PQescapeBytea Escapes a binary string bytea type for use
331. rminated 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 avail able or a positive number giving 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 PQput line 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 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 EOF if unable to send the string int PQputnbytes PGconn conn const char buffer int nbytes Thi
332. rocessed 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 SELECT 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 results 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 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 loop 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
333. rocessing 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 lan guage 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 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
334. rocessor 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 EXEC SQL statement can be one of these 71 Chapter 6 ecpg Embedded SQL in C Declare sections Declare sections begin with exec sql begin declare section and end with xec sql end declare section In this section only variable declarations are allowed Every variable declared within this section is stored in a list of variables indexed by name together with its corresponding type In particular the definition of a structure or union also must be listed inside a declare section Otherwise ecpg cannot handle these types since it does not know the definition The declaration is also echoed to the file to make it a normal C variable 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 Include statements An include statement looks like exec sql include filename Note that this is NOT the same as include lt filename h gt Instead the file specified is parsed by ecpg so the contents of the file are included in the res
335. ropriate indexes setup the planner will create a plan of Nestloop gt Index Scan using comp_hostidx on computer gt 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 gt Seq Scan on software gt Hash gt Index Scan using comp_hostidx on computer The other possible query is a DELETE FROM computer WHERE hostname old with the execution plan Nestloop gt Index Scan using comp_hostidx on computer gt Index Scan using soft_hostidx on software 226 Chapter 16 The Rule System 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
336. rows from the access method appear here The object ID of the row in pg_am is used as a foreign key in a lot of other tables You do not need to add a new row to this table all that you are interested in is the object ID of the access method you 228 Chapter 17 Interfacing Extensions To Indexes want to extend SELECT oid FROM pg_am WHERE amname btree We will use that query in a WHERE clause later 17 3 Access Method Strategies The amstrategies column exists to standardize comparisons across data types For example B trees impose a strict ordering on keys lesser to greater Since PostgreSQL allows the user to define operators PostgreSQL cannot look at the name of an operator e g gt or lt and tell what kind of comparison it is In fact some access methods don t impose any ordering at all For example R trees express a rectangle containment relationship whereas a hashed data structure expresses only bitwise similarity based on the value of a hash function PostgreSQL needs some consistent way of taking a qualification in your query looking at the operator and then deciding if a usable index exists This implies that PostgreSQL needs to know for example that the lt and gt operators partition a B tree PostgreSQL uses strategies to express these relationships between operators and the way they can be used to scan indexes Defining a new set of strategies is beyond the scope
337. rr_quant current_user current_timestamp 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 shoelace_data OLD shoelace_data NEW shoelace_log shoelace_log bpchareq s sl_name showlace_arrive arr_name bpchareq shoelace_data sl_name s sl_name int4ne int4pl s sl_avail shoelace_arrive arr_quant s sl_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 INS F WH UPD F WH ERT RO ERE AND AND ATE RO ERE AND INTO shoelace_log SELECT s sl_name s sl_avail shoelace_arrive arr_quant current_user current_timestamp shoelace_arrive shoelace_arrive shoelace_data shoelace_data shoelace_data s s sl_name shoelace_arrive arr_name shoelace_data sl_name s sl_name s sl_avail shoelace_arrive arr_quant s sl_avail shoelace_data SET sl_avail shoelace_data sl_avail shoelace_arrive arr_quant shoelace_arrive shoelace_arrive shoelace_data shoelace_data shoelace_data s s sl_name shoelace_arrive sl_name shoelace_data sl_name s sl_name The result is that data coming from one relation inserted
338. rror Invalid connection or invalid object Description unlink method unlinks deletes the large object 162 size Name size gives 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 opened 163 export Name export saves 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 164 Chapter 9 PyGreSQL Python Interface 9 7 DB API Interface See http www python org topics database DatabaseAPI 2 0 html for a description of the DB API 2 0 165 ll Server Programming This second part of the manual explains the PostgreSQL approach to extensibility and describe how users c
339. ryStream 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 ina 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 img 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 89 Chapter 8 JDBC Interface Alternatively you could be storing a very large file and want to use the LargeObject API to store the file CREATE TABLE imagesLO imgname text imgOID OID To insert an image you would use 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 Connection conn getLargeObjectAPI create a new large object int oid lobj create LargeObjectManager READ LargeObjectManager WRIT Gl open the large object for write LargeObject obj lobj open oid LargeObjectManage
340. s 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 12 7 Several procedural languages are available in the standard PostgreSQL distribution which can serve as examples 22 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 template 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 createlang may be used instead of carrying out the details by hand For example to install PL pgSQL into the template 1 database use createlang plpgsql templatel The manual procedure described below is only recommended for installing custom languages that createlang 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 s
341. s as indicated by PQst atus 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 PQresetPol1 Reset the communication port with the backend in a nonblocking manner int PQresetStart PGconn conn PostgresPollingStatusType PQresetPoll PGconn conn These functions will close the connection to the backend and attempt to reestablish a new connec tion to the same server using all the same parameters previously used This may be useful for error recovery if 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 PQconnectPoll Call POresetStart If it returns 0 the reset has failed If it returns 1 poll the reset using PQre setPoll in exactly the same way as you would create the connection using POconnectPoll Chapter 1 libpg C Library libpq application programmers should be careful to maintain the PGconn abstraction Use the accessor functions below to get at the contents of PGconn Av
342. s at each index tuple All the costs are assumed to be paid incrementally during the scan z 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 pg_statistic If the correlation is not known the conservative estimate is zero no correla tion 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 prorettype 0 pronargs 8 proargtypes 00000000 We use zero opaque for all the arguments since none of them have types that are known in pg_type 236 Chapter 19 GiST Indexes The information about GIST is at http GiST CS Berkeley EDU 8000 gist with more on different indexing and sorting schemes at http s2k ftp CS Berkeley EDU 8000 personal jmh And there is more interesting reading at http epoch cs berkeley edu 8000 and http www sai msu su megera postgres gist Author This extraction from an email sent by Eugene Selkov Jr lt selkovjr mcs anl gov gt contains good information on GiST Hopefully we will learn more in the future and update this information thomas 1998 03 01 Well I can t say I quite understand what s going on but at least I almost succeeded in porting GiST examples to linux The GiST a
343. s is exactly like PQput 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 been sent to the backend using PQput line 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 17 Chapter 1 libpg C Library 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 PQputline conn 4 tgoodbye world t7 11 n PQputline conn n PQendcopy conn When using PQgetResult the application should respond to a PGRES_COPY_OUT result by execut ing PQgetline repeatedly followed by PQendcopy after the terminator line is seen It should then return to the POgetResult loop until PQgetResult returns NULL Similarly a PGRES_COPY_IN result is processed by a series of POput Line calls followed by PQendcopy then return to the PQge tResult loop This arrangement will ensure that a copy in or copy out command embedded in a se
344. s like this ERROR function declared to return emp returns varchar instead of text at column In the present release of PostgreSQL there are some unpleasant restrictions on how functions returning composite types can be used Briefly when calling a function that returns a row we cannot retrieve the entire row We must either project a single attribute out of the row or pass the entire row into another function Trying to display the entire row value will yield a meaningless number For example SELECT name new_emp This example makes use of the function notation for projecting attributes The simple way to explain this is that we can usually use the notations attribute table and table attribute inter changeably this is the same as SELECT EMP name AS youngster FROM EMP WHERE EMP age lt 30 SELECT name EMP AS youngster FROM EMP WHERE age EMP lt 30 youngster The reason why in general we must use the function syntax for projecting attributes of function return values is that the parser just doesn t understand the dot syntax for projection when combined with function calls SELECT new_emp name AS nobody ERROR parser parse error at or near 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 F
345. s passed to the function in the TriggerData structure The purpose of passing ar guments to the function is to allow different triggers with similar requirements to call the same function Also procedure may be used for triggering different relations these functions are named as general trigger functions As example of using both features above there could be a general function that takes as its arguments two field names and puts the current user in one and the current timestamp in the other This allows triggers to be written on INSERT events to automatically track creation of records in a transaction table for example It could also be used as a last updated function if used in an UPDATE event Trigger functions return HeapTuple to the calling Executor This is ignored for triggers fired after an INSERT DELETE or UPDATE operation but it allows BEFORE triggers to e Return NULL to skip the operation for the current tuple and so the tuple will not be inserted updated deleted e Return a pointer to another tuple INSERT and UPDATE only which will be inserted as the new version of the updated tuple if UPDATE instead of original tuple Note that there is no initialization performed by the CREATE TRIGGER handler This will be changed in the future Also if more than one trigger is defined for the same event on the same relation the order of trigger firing is unpredictable This may be changed in the future If a trigger function
346. s returns the number of tuples rows in the query result int PgDatabase Tuples const e Fields returns the number of fields rows in each tuple of the query result int PgDatabase Fields FieldName returns the field column name associated with the given field index Field indices start at 0 const char PgDatabase FieldName int field_num const e FieldNum returns the field column index associated with the given field name int PgDatabase FieldNum const char field_name const 1 is returned if the given name does not match any field e FieldtType 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 PgDatabase FieldType int field_num const e FieldtType returns the field type associated with the given field name The integer returned is an internal coding of the type Field indices start at 0 Oid PgDatabase FieldType const char field_name const e FieldSize returns the size in bytes of the field associated with the given field index Field indices start at 0 int PgDatabase FieldSize int field_num const Returns the space allocated for this field in a database tuple given the field number In other words the size of the server s binary representation of the data type 1 is returned if the field is variable size e FieldSize returns the size in bytes of the field associated with the given field index Field indices s
347. s sisi nen aa N Scean E A E a A ONENA 121 Betsdertly e E ee Re een Mee eke hate a ease 122 Set detty scvecsveueescntvesscelvescnssvesiersunstcetosupdesetiestecnisetinedauseeseg cesta susavdvesbanedvenenttnetevnetes 123 petodefbase n nesae tekcd eed cassensdeavacebunsn tapes beoantevsndel ETO EEEE 124 SEL CET L 1 R E EEE et ete tae A EE 125 9 3 Connection object pohje nnna eaer EEEE E E E E 126 QUIET Y AEE S EE EEEE E EEA E 126 RA A EEE EA AE EAE A E A EEE AE A tee AEE 128 O OTI E E E E E E IE S EE ee 129 MUSTO 25528 E E E E AEE EE E A EE E E E E 130 POMOtlys ieee Aes TTT E 131 INSET ADI eA oc eee A E E A EEE EE EA 132 Pute eiiis se E ee a E E E E R E ae hectares 133 POT ics wd E E E R E ee hanes Bi eer eesets 134 COU eLa OA A R ERENER E EE ETT eee 135 VOGT E AEA E ENA E EEE EE E EA ENA O EE AE ENA EEEE 136 PEO e E e E R E a E E E E ERE S 137 LOUMPOMb in ea a oeae E EEE E T EEE EEEE EEE 138 9 4 Database wrapper Class DB iscc c ssscccss cbs csssessscsbesvesseashesbgedstesess yes sasvadcasdbcesdesveeveess 139 PREY Acs E leh etic eee A ein ead don Aes re E aaah Meese tees 139 get databases iscecseivserseriesiacsseeevacnaaaeays soseaa ES EAS E EEE R 141 pet table Snn E E A a a a a 142 AEAEE AnA AVEN 1 1 SAPERE EEE TTET 143 DOL EEE E E E E E E EET 144 INE a ER AE E E E A ES 145 Update eie nr ea e E e bn a E E abies 146 0 E ce E Aik ond EEPE EAE EEA ETTA R A AERE 147 C6 2 2 i A EN AEA EE E EE E E A ee 148 9 5 Query result object pgquery
348. se 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 NULLs 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 There is a special variable named FOUND of type boolean that can be used immediately after a SELECT INTO to check if an assignment had success that is at least one row was returned by the SELECT 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 IS NULL or ISNULL conditional to test for NULLity of a RECORD ROW result Note that there is no way to tell whether any additional rows might have been discarded DECLARE users_rec RECORD full_name varchar 298 Chapter 23 PL pgSQL SQL Procedural Language BEGIN SELECT INTO users_rec FROM users WHERE user_id 3 IF users_rec homepage IS NULL THEN use
349. simple refcursor vari able The query is specified as a string expression in the same way as for the EXECUTE command As usual this gives flexibility for the query to vary from one run to the next OPEN cursl FOR EXECUTE SELECT FROM quote_ident 1 23 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 into 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 23 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 refcursor value out of a function and let the caller operate on the cursor Internally a refcursor 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 307 Chapter 23 PL pgSQL SQL Procedural Language All Portals are implicitly closed at end of transaction Therefore a ref
350. sl_avail 6 WHERE sl_name sl1l7 These are executed in this order and that is exactly what the rule defines The substitutions and the qualifications added ensure that if the original query would be say T UPDATE WHERE shoelace_data SET sl_color green sll sl_name no log entry would get written This time the original parse tree does not contain a target list entry for sl_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 T UPDATE WHERE 0 shoelace_data SET sl_avail black sl_color 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 0 current_user current_timestamp FROM shoelace_data WHERE 0 shoelace_data sl_avail AND shoelace_data sl_color black This parse tree will surely insert three new
351. so be found in funcs sql and funcs c in the tutorial directory Throughout this chapter it can be useful to look at the reference page of the CREATE FUNCTION command to understand the examples better 12 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 multi row 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 sometype 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 semi colons 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 type then
352. 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 debug 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 buttons 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 16 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 205 Chapte
353. ss 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 PGbox in the syntax expected by PostgreSQL Overrides getValue in class PGobject Class org postgresql geometric PGcircle java lang Object org postgresql util PGobject org postgresql geometric PGcircle public class PGcircle extends PGobject implements Serializable Cloneable This represents PostgreSQL s circle data type consisting of a point and a radius Variables public PGpoint center This is the center point double radius This is the radius 97 Chapter 8 JDBC Interface Constructors public public public public Methods public public public PGcircle double x double y double r Parameters x coordinate of center y coordinate of center r radius of circle PGcircle PGpoint c double r Parameters c PGpoint describing the circle s center r radius of circle PGcircle String s throws SQLException Parameters s definition of the circle in PostgreSQL s syntax Throws SQLException 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
354. ssed into the function the name of the desired attribute and a return parameter that tells whether the attribute is null Getat tributeByName returns 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 While there are ways to construct new rows or modify existing rows from within a C function these are far too complex to discuss in this manual Consult the backend source code for examples 188 Chapter 12 Extending SQL Functions 12 5 6 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 and the malloc memory manager 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 assume that your programming language functions are written in C The
355. st char PgConnection DBName e Notifies returns the next notification from a list of unhandled notification messages received from the backend PGnotify PgConnection Notifies See PQnotifies in libpq for details 3 5 Query Execution Functions 3 5 1 Main Routines Exec sends a command to the backend server It s probably more desirable to use one of the next two functions ExecStatusType PgConnection Exec const char query Returns the result status of the command The following status results can be expected PGRES_EMPTY_QUERY PGRES_COMMAND_OK if the command was not a query PGRES_TUPLES_OK if the query successfully returned tuples PGRES_COPY_OUT PGRES_COPY_IN PGRES_BAD_RESPONSE if an unexpected response was received PGRES_NONFATAL_ERROR PGRES_FATAL_ERROR 40 Chapter 3 libpq C Binding Library ExecCommandOk sends a non query command one that does not return rows to the backend server int PgConnection ExecCommandOk const char query Returns true 1 if the command succeeds ExecTuplesOk Sends a query command one that returns rows to the backend server int PgConnection ExecTuplesOk const char query Returns true 1 if the query succeeds ErrorMessage returns the last error message text const char PgConnection ErrorMessage 3 5 2 Retrieving SELECT Result Information Tuple
356. statement following END LOOP is executed next If 1abe1 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 303 Chapter 23 PL pgSQL SQL Procedural Language LOOP some computations IF count gt 0 THEN EXIT exit loop END IF END LOOP LOOP some computations EXIT WHEN count gt 0 END LOOP BEGI some computations IF stocks gt 100000 THEN EXIT illegal Can t use EXIT outside of a LOOP END IF 23 6 3 3 WHILE 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 ND LOOP al WHILE NOT boolean_expression LOOP some computations here ND LOOP Fl 23 6 3 4 FOR integer for loop lt lt label gt gt FOR name IN REVERSE expression expression LOOP statements END LOOP This form o
357. stgreSQL how to use a user defined type and or user defined operators with an index i e pg_am pg_amop pg_amproc pg_operator and pg_opclass Unfortunately there is no simple com mand to do this We will demonstrate how to modify these catalogs through a running example a new operator class for the B tree access method that stores and sorts complex numbers in ascending absolute value order 17 2 Access Methods The pg_am table contains one row for every index access method Support for the heap access method is built into PostgreSQL but all other access methods are described in pg_am The schema is shown in Table 17 1 Table 17 1 Index Access Method Schema Column Description lamname name of the access method lamowner user ID of the owner currently not used lamstrategies number of strategies for this access method see below lamsupport number of support routines for this access method see below lamorderstrategy zero if the index offers no sort order otherwise the strategy number of the strategy operator that describes the sort order lamcanunique does AM support unique indexes lamcanmulticol does AM support multicolumn indexes lamindexnulls does AM support NULL index entries lamconcurrent does AM support concurrent updates lamgettuple laminsert procedure identifiers for interface routines to the access method For example regproc IDs for opening closing and getting
358. sult object can be modified rv plpy execute SELECT FROM my_table 5 returns up to 5 rows from my_table Ff my_table has a column my_field it would be accessed as foo rv i my_field 335 Chapter 26 PL Python Python Procedural Language 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 plan plpy prepare SELECT last_name FROM my_users WHERE first_name 1 text is the type of the variable you will be passing as 1 After preparing you use the function plpy execute to run it rv plpy execute plan name 5 The limit argument is optional in the call to plpy execute When you prepare a plan using the PL Python module it is automatically saved Read the SPI docu mentation Chapter 21 for a description of what this means The take home message is if you do plan plpy prepare SOME QUERY plan plpy prepare SOME OTHER QUERY you are leaking memory as I know of no way to free a saved plan The alternative of using unsaved plans it even more painful for me 336 text Bibliography Selected references and readings for SQL and PostgreSQL Some white papers and technical reports from the original POSTGRES development team are avail able at the University of California Berkeley Computer Science Department web site SQL Reference
359. t 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 s as in Example 23 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 23 1 gives the scoop You ll love this little chart Table 23 1 Single Quotes Escaping Chart No of Quotes Usage Example Result 1 http www arsdigita com 2 http www arsdigita com asj clickstream 3 http www openforce net 312 Chapter 23 PL pgSQL SQL Procedural Language 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 plpgsql 2 In assignments a_output Blah jSELECT FROM SELECTS to delimit SE users WHERE Strings etc LECT FROM users WAERIm nioebdifopbar 4 When you need two a_output a_outpuAND ndmANDIKEme LIKE foo single quotes in your bar AND a foobar AND resulting string without terminating that string 6 When you want double ja_output a_outpyANp n m ND IK me LIKE foo quotes in your resulting bbar foobar string and terminate
360. t however Regardless of the return value of PQrequestCancel the application must con tinue with the normal result reading sequence using POgetResult 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 command then there will be no visible result at all Note that if the current command is part of a transaction cancellation will abort the whole transaction PQrequestCancel can safely be invoked from a signal handler So it is also possible to use it in conjunction 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 14 Chapter 1 libpg C Library 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 ar
361. t execute his operations this many times For example There are two tables CREATE TABLE computer hostname text indexed manufacturer text indexed 225 Chapter 16 The Rule System CREATE TABLE software software text indexed hostname text indexed di 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 computer it can use the statement DELETE FROM software WHERE hostname 1 in a prepared and saved plan and pass the hostname 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 app
362. t 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 tem porarily set the state of the connection to blocking until the PQexec completes More of libpq is expected to be made safe for PQsetnonblocking functionality in the near future 12 Chapter 1 libpg C Library 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 PQerrorMessage to get more information about the failure int PQsendQuery PGconn conn const char query After successfully calling PQsendQuery call PQget Result one or more times to obtain the re sults POQsendQuery may not be called again on the same connection until PQget Result has returned NULL indicating that the command is done PQgetResult Wait for the next result from a prior POsendQuery and return it NULL is returned when the query is complete and there will be no more results PGresult PQgetResult PGconn conn PQgetResult must be called repeatedly until it returns NULL indicating that the command is done If called when no command is active POgetResult will just return NULL at once Each non NULL
363. t linus epact se gt and Michael Meskes lt meskes debian org gt The pack age is installed with the PostgreSQL distribution and carries a similar license 6 1 Why Embedded SQL Embedded SQL has advantages over other methods for handling SQL queries It takes care of the tedious passing of information to and from variables in your C or C program Many RDBMS packages support this embedded language There is an ANSI standard describing how the embedded language should work ecpg was designed to match this standard as much as possible It is possible to port embedded SQL programs written for other RDBMS to PostgreSQL 6 2 The Concept You write your program in C C with special SQL constructs When declaring variables to be used in SQL statements you need to put them in a special declare section You use a special syntax for the SQL queries Before compiling you run the file through the embedded SQL C preprocessor and it converts the SQL statements you used to function calls with the variables used as arguments Both query input and result output variables are passed After compiling you must link with a special library that contains needed functions These functions fetch information from the arguments perform the SQL query using the 1ibpq interface and put the result in the arguments specified for output 6 3 How To Use ecpg This section describes how to use ecpg 6 3 1 Preprocessor The preprocessor is called ecpg Af
364. tabase 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 Ad vanced 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 language support and other modern features POSTGRES pioneered many of the object relational concepts now becoming available in some com mercial databases Traditional relational database management systems RDBMS support a data model consisting 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 inadequate for future data processing appli cations 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 e inheritance e data types e functions Other features provide additional power and flexibility constr
365. tables plus the restrictive qualifications 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 16 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 16 4 Rules on INSERT UPDATE and DELETE 16 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 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 plac
366. tart at 0 int PgDatabase FieldSize const char field_name const 41 Chapter 3 libpq C Binding Library Returns the space allocated for this field in a database tuple given the field name In other words the size of the server s binary representation of the data type 1 is returned if the field is variable size 3 5 3 Retrieving SELECT Result Values e GetValue returns a single field column value of one tuple of a PGresult Tuple and field indices start at 0 const char PgDatabase GetValue int tup_num int field_num const For most queries the value returned by GetValue is a null terminated string representation of the attribute value But if BinaryTuples is true the value returned by GetValue 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 Get 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 BinaryTuples is not yet implemented e GetValue returns a single field column value of one tuple of a PGresult Tuple and field indices start at 0 const char PgDatabase GetValue int tup_num const char field_name const For most que
367. tatement looks like exec sql commit Rollback statement A rollback statement looks like exec sql rollback Other statements Other SQL statements are used by starting with exec sql and ending with Everything in be tween is treated as an SQL statement and parsed for variable substitution Variable substitution occurs when a symbol starts with a colon The variable with that name is looked up among the variables that were previously declared within a 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 73 Chapter 6 ecpg Embedded SQL in C 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 it is 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 e A pointer to the value of the indicator variable or a pointer to the pointer of the indicator variable e 0 e Number of elements in the indicator array for array fetches The offset to the next element in the indicator array for array fetches 6 6 2 A Complete Example Here is a complete example describing the output of the preprocessor of a file foo pgc
368. tch void param int fetchwithnulls void param void reset_fetch void on_error_continue void on_error_stop PGresult get_result void set_result PGresult newres void unset_result PGresult oldres Many functions return a structure or value so you can do more work with the result if required You basically connect to the database with connectdb issue your query with doquery fetch the results with fetch and finish with disconnectdb For SELECT queries fetch allows you to pass pointers as parameters and on return the variables are filled with data from the binary cursor you opened These binary cursors cannot be used if you are running the pgeasy client on a system with a different architecture than the database server If you pass a NULL pointer parameter the column is skipped fet chwithnull1s allows you to retrieve the NULL status of the field by passing an int after each result pointer which returns true or false if the field is null You can always use libpq functions on the PGresult pointer returned by doquery reset_fetch Starts the fetch back at the beginning get_result set_result and unset_result allow you to handle multiple result sets at the same time There are several demonstration programs in the source directory 66 Chapter 6 ecpg Embedded SQL in C This describes the embedded SQL package for PostgreSQL It works with C and C It was written by Linus Tolke l
369. te queries Some utility SPI functions may be called from un connected procedures If your procedure is already connected SPI_connect will return an SPILERROR_CONNECT er ror 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 247 SPI finish Name SPI_finish Disconnects your procedure from the SPI manager Synopsis SPI_finish void Inputs None Outputs int SPI_OK_FINISH if properly disconnected SPI_LERROR_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 completing 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 hav ing 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 t
370. ter installation it resides in the PostgreSQL bin directory 6 3 2 Library The ecpg library is called libecpg a or libecpg so Additionally the library uses the 1ibpq library for communication to the PostgreSQL server You will have to link your program using lecpg 1pq The library has some methods that are hidden but may prove useful 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 67 The most important function 1 Chapter 6 ecpg Embedded SQL in C 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 6 3 3 Error handling To detect errors from the PostgreSQL server include a line like exec sql include sqlca in the include section of your file This will define a struct and a variable with the name sqica as follows struct sqlca char sqlcaid 8 long sqlabc long sqlcode struct int sqlerrml char sqlerrmc 70 sqlerrm char sqlerrp 8 long sqlerrd 6 0 empty 1 OID of processed tuple if applicable 2 number o
371. tgres although many systems are installed that way Furthermore the Post greSQL 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 169 Chapter 11 Extending SQL An Overview In the sections that follow we will discuss how you can extend the PostgreSQL SQL query language by adding e functions e data types e operators e aggregates 11 1 How Extensibility Works PostgreSQL is extensible because its operation is catalog driven If you are familiar with standard relational systems you know that they store information about databases tables columns etc in what are commonly known as system catalogs Some systems 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 functions 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 on
372. the dot notation e g 1 emp may be used to access attributes of the argument 12 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 174 Chapter 12 Extending SQL Functions UPDATE bank SET balance balance 2 WHERE accountno 1 SELECT 1 LANGUAGE SQL A user could execute this function to debit account 17 by 100 00 as follows SELECT tp1 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 CREATE FUNCTION clean_EMP RETURNS integer AS DELETE FRO EMP WHERE EMP salary lt 0 SELECT 1 AS ignore_this LANGUAGE SQ
373. 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 Missing columns of the result relation 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 old ones In the rule system it contains just the expressions from the SET attribute expression part of the query The planner will add 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 the qualification The query s qualification is an expression much like one of those contained in the target list entries The
374. the information on the TODO list report your problem The least we can do is make the TODO list clearer 5 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 from 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 fro
375. the point with the supplied amount 105 Chapter 8 JDBC Interface 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 refer to java awt Point for description of this Parameters x integer coordinate y integer coordinate See Also Point public void setLocation Point p Moves the point to the supplied java awt Point refer to java awt Point for description of this Parameters p Point to move to See Also Point Class org postgresql geometric PGpolygon java lang Object org postgresql util PGobject org postgresql geometric PGpolygon public class PGpolygon extends PGobject implements Serializable Cloneable 106 Chapter 8 JDBC Interface This implements the polygon data type within PostgreSQL Variables public PGpoint points The points defining the polygon Constructors public 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
376. 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 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 e 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 operator 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
377. 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 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 6 Y2K Statement Author Written by Thomas Lockhart lt lockhart fourpalms org gt on 1998 10 22 Updated 2000 03 31 The PostgreSQL Global Development Group provides the PostgreSQL software code tre
378. tion s name This is not char but NameData Use SPI_getrelname tg_relation to get char if you need a copy of name 241 tg_trigtuple Chapter 20 Triggers 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 if 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 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 src include utils rel h typedef struct Trigger int16 int16 char Trigger tgoid tgname tgfoid tgtype tgenabled tgisconstraint tgdeferrable tginitdeferred tgnargs tgattr FUNC_MAX_ARGS xtgargs 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 20 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
379. tion to a backend server To create such an object one first needs the appropriate environment for the backend to access The following con structors deal with making a connection to a backend server from a C program 3 4 Database Connection Functions PgConnection makes a new connection to a backend database server PgConnection PgConnection const char conninfo 39 Chapter 3 libpq C Binding Library The conninfo string is the same as for the underlying libpq PQconnect db function Although typically called from one of the access classes a connection to a backend server is possi ble by creating a PgConnect ion object ConnectionBad returns whether or not the connection to the backend server succeeded or failed bool PgConnection ConnectionBad const Returns true if the connection failed Status returns the status of the connection to the backend server ConnStatusType PgConnection Status Returns either CONNECTION_OK or CONNECTION_BAD depending on the state of the connection PgDatabase makes a new connection to a backend database server PgDatabase const char conninfo After a PgDatabase has been created it should be checked to make sure the connection to the database succeeded before sending queries to the object This can easily be done by retrieving the current status of the PgDatabase object with the Status or Connect ionBad methods DBName returns the name of the current database con
380. 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 context 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_palloc are made in this context When a procedure disconnects from the SPI manager via SPI_finish the current context is re stored 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 272 Inputs HeapTuple tuple Input tuple to be copied Outpu
381. ts PEOLACE T esa nsbesvisassdsocbsbesndvesoisaes sesesnsve bi sass sosbsbastivesesnave dvesesnsve biased E ETEA xii 1 Whats PostgreSQL raees ihesian perea ee oteier EEE RES xii 2 A Short History of PostgreSQL rennin e E EE AE E E ERES xii 2A The Berkeley POSTORES Projecta oisein o E S xiii 2 24 POSISIES J a a Se Ree SS xiii 23e Postgre SQ Lre ip e AE OE EEE ETES AOS ses VEE EEEE E SREE SREE TERS xiv 3 Documentation RESOUTCES sisne ececeseeeeeeeeceesscsecsceeeeeseaecaeesaecaecsscseeseseesesacsaecaecasenaeees xiv As Terminology and Notation orninn R EE N EERE ONE E a XV 5 Bug Reporting Guidelines ee eeeesecsecsseeseeescesceseeeeecaecsaesaeceecesceseseeseasesaesaecsecseenaeees xvi 3 1 Adentityine BUES rre nran a oaa ee eepe s ae e o aia keisi xvi X2 What to reporte erap E er eine a ee ates R OE xvii 5 34 Where to teport DUBS saien i e Aa Ee E E Ea xviii OG Y2K Statement enn ee A A a es xix I Client Interfaces ssssssssssssrscssrssssssesessserersesessessssesssecsssscsesscsesessesessesessesessessnscssnsccesescesensesonseses 1 T libpg C Library sisi kes el nik lathe ee aa e il nies Disk aaa E ae heeees tel eoc se dunbes Soest aes 1 VV Titre Au Ct On sess sss sili aes EEEE EEE sew steshesdsaphess che sasvages scbepets esses esse 1 1 2 Database Connection Functions 00 0 0 cece ceeeeeeeeeeeceeesseceececeseeeeseaeeaeesaecaecseceseeeeees 1 1 3 Command Execution Functions 00 0 cece cececeeeeeeeceseeseecaeceecaeeseeseceaeeseeeaec
382. ts 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 273 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 274 SPI_copytupleintoslot Name SPI_copytupleintoslot Makes copy of tuple and descriptor in upper Executor context 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 275 SPI_modifytuple Name SPI_modifytuple Creates a tuple by replacing selected fields of a given tuple Synopsis SPI_modifyt
383. ts 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 signal the trigger manager to skip the rest of the operation for this row ie subsequent triggers are not fired and the INSERT UPDATE DELETE does not occur for this row If a non NULL value is returned then the operation 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 23 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 last_user text CREATE FUNCTION emp_stamp RE BEGIN Check that empname and s
384. u mark merge joinable These restrictions are not currently checked by CREATE OPERATOR but a merge join may fail at run time if any are not true The merge joinable equality operator must have a commutator itself if the two data types are the same or a related equality operator if they are different There must be lt and gt ordering operators having the same left and right operand data types as the merge joinable operator itself These operators must be named lt and gt you do not have any choice in the matter since there is no provision for specifying them explicitly Note that if the left and right data types are different neither of these operators is the same as either SORT operator But 201 Chapter 14 Extending SQL Operators they had better order the data values compatibly with the SORT operators or the merge join will fail to work 202 Chapter 15 Extending SQL Aggregates Aggregate functions 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 aggre
385. u sisedsestaaseatcoasvnss EA EE TEE 339 List of Tables ALD pig Cl COMMANAS 30 54 Fc cast ceded e e e a e o a r ea e oree iae 45 11 1 PostgreSQL System Catalogs s enesersreeesesrerersererseseeressererersverseererernereroreeertererersreenseerereree ress 171 12 1 Equivalent C Types for Built In PostgreSQL Types ssessesessesseeessereseesseeersresrrersrerrsreseresseees 181 17 1 Index Access Method Schema esssseeeeessseessseeresrsseerssrsrsresterrsreersrenrertsrerrsreerstenreesresesesseeeee 228 17 2 Batre State BIOS iser oie e peo i spevoes az EOE EE ERES RENREN ip e SEEE ES TA EEE S EREN ES 229 23 1 Single Quotes Escaping Chart sseeeesseeeesesesrseserrsseeesrsserrssenreststestsstntesrnrerresersrenteresreresee 312 List of Figures 10 1 How a connection is established cee eesceececeeceesecencecereessecesceeeeesaecesceseeeesseseaeeeeecaeeeaeeesees 167 11 1 The major PostgreSQL system catalogs eee eseesececeeeeeeeesecseesaecaececeseeeeseaeeseesaecseesensees 171 List of Examples 11 hibpg Example Program oso scceedss secede aa aaa raa ae A E A A ER AA ses a i ia Einin 21 1 2 ibpg Example Progra 2 eccere erroei OaE E a i ventas A ai aai at a 24 1 3 libpq Example Program 3 3 eicscscescisusccasesvye segs eter setckiespeseseas oeeie E esre E E EEEE reS Erai tes 26 2 1 Large Objects with Libpq Example Program s eeesssseesessserssrsresesrssesrssreresrsrerreeersrenrerrsreersrent 33 4 1 pstcl Example Prog
386. ulting C code This way you are able to specify EXEC SQL commands in an include file Connect statement A connect statement looks like exec sql connect to connection target It creates a connection to the specified database The connection target can be specified in the following ways e dbname server port as connection name user user name e tcp postgresql server port dbname as connection name user user name e unix postgresql server port dbname as connection name user user name e character variable as connection name user user name e character string as connection name user e default Ser 72 Chapter 6 ecpg Embedded SQL in C There are also different ways to specify the user name e userid e userid password e userid identified by password e userid using password Finally the userid and password may be a constant text a character variable or a character string Disconnect statements A disconnect statement looks like exec sql disconnect connection target It closes the connection to the specified database The connection target can be specified in the following ways e connection name e default current e all Open cursor statement An open cursor statement looks like exec sql open cursor and is not copied to the output Instead the cursor s DECLARE command is used because it opens the cursor as well Commit statement A commit s
387. unction 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 statement A call handler can avoid repeated lookups of information about the called function by using the flinfo gt fn_extra field This will initially be NULL but can be set by the call handler to point at information about the PL function On subsequent calls if f1info gt fn_extra is already non NULL then it can be used and the in formation lookup step skipped The call handler must be careful that flinfo gt fn_extra is made to point at memory that will live at least until the end of the current query since an FmgrInfo data structure could be kept that long One way to do this is to allocate the extra data in the memory context specified by fl1info gt fn_mcxt such data will normally have the same lifespan as the FmgriInfo 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
388. unction 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 33 Chapter 25 PL Perl Perl Procedural Language CREATE TABLE employee name text basesalary integer bonus integer i CREATE FUNCTION empcomp employee RETURNS integer AS my Semp _ return Semp gt basesalary Semp gt bonus LANGUAGE plperl SELECT name empcomp employee FROM employee There is not currently any 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 functions q qq 1 qwf 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 gt tmp badfile print TEMP Gotcha n return 1 LANGUAGE plperl The creation of the function will succeed but executing it will not Note that if the same function was created by a superuser using language plperlu execution would succeed
389. unction 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 CREATE FUNCTION statement Something like CREATE FUNCTION foo RETURNS INTEGER AS LANGUAGE plpgsql WITH isstrict iscachable 23 11 6 Appendix 23 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 occurrence of string2 If n is negative search backwards If m is not passed assume 1 search starts at first character by Roberto Mello rmello fsic usu edu modified by Robert Gaszewski graszew poland com Licensed under the GPL v2 or later Q REATE FUNCTION instr VARCHAR VARCHAR RETURNS INTEGER AS ECLARE pos integer BEGIN pos instr 1 2 1 RETURN pos iw LANGUAGE plpgsql CREATE FUNCTION instr VARCHAR VARCHAR INTEGER RETURNS INTEGER AS ECLARE string ALIAS FOR 1 iw 320 string beg_in pos in temp_s beg IN length ss_len BEGIN IF beg Chapter 23 PL pgSQL SQL Procedural Language _to_search ALIAS FOR 2 dex ALIAS FOR 3 teger NOT NULL DE
390. up ports arrays of user defined types as well When you define a type PostgreSQL automatically pro vides 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 they look like inside If the values of your datatype 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 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 196 Chapter 14 Extending SQL Operators 14 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 opera
391. uple 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 SPL_result SPI_LERROR_ARGUMENT if rel is NULL or tuple is NULL or natts lt 0 or attnum is NULL or Values is NULL SPI_LERROR_NOATTRIBUTE if there is an invalid attribute number in attnum attnum lt 0 or gt number of attributes in tuple 276 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 277 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_p
392. urces sooner 261 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 SPL result SPI_LERROR_ARGUMENT if plan is NULL SPI_LERROR_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 alterna tive 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 Usage 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 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 SPI_execp for this plan will be unpredictable 262 SPI_saveplan 263
393. ut down there is probably no good reason to use this error level in PL Tcl functions but it s provided for completeness 24 2 5 Trigger Procedures in PL Tcl Trigger procedures can be writt en 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 opaque 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 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 fields are customarily numbered in PostgreSQL STG_when The string BE FORE or AFT ER depending on the type of trigger call STG_level M The string ROW or STATE ENT depending on the type of trigger call 327 Chapter 24 PL Tcl Tcl Procedural Language STG_op Wy The string INSERT UPDATE or DELETE 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
394. ve 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 Connection It is up to you and your applications requirements 8 9 Further Reading If you have not yet read it Pd 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 in cludes precompiled drivers 112 Chapter 9 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 Further modifica tions Copyright 1997 2000 by D Arcy J M Cain 9 1 The pg Module 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 DatabaseA PI 2 0 html A tutori
395. ving SELECT Result Information PQntuples Returns the number of tuples rows in the query result int PQntuples const PGresult res e PQnfields Returns the number of fields columns in each row of the query result int PQnfields const PGresult res Chapter 1 libpg C Library PQfname Returns the field column name associated 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 const char field_name 1 is returned if the given name does not match any field PQftype 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 PQftype 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 PQfmod 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 e PQfsize 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 PQfsize returns the space allocate
396. with the additional 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 198 Chapter 14 Extending SQL Operators 14 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 NOTs can be inserted as a consequence of other rearrangements Pairs of negator operators can be defined using the same methods expla
397. 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 and backslash 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 from_length parameter reflects the number of characters in this binary string a terminating zero byte is neither necessary nor counted The to_length parameter shall point to a buffer suitable to hold the resultant escaped string length The result string length does not include 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 1 3 4 Retrie
398. word authentication This is not recommended because the password can be read by others using the ps command with special options on some platforms PGREALM sets the Kerberos realm to use with PostgreSQL if it is different from the local realm If 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 runtime options for the PostgreSQL backend e PGTTY sets the file or tty on which debugging messages from the backend server are displayed The following environment variables can be used to specify user level default behavior for every PostgreSQL session PGDATESTYLE Sets the default style of date time representation e PGTZ sets the default time zone 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 SQL command for information on correct values for these environment variables 3 3 libpq Classes 3 3 1 Connection Class PgConnection The connection class makes the actual connection to the database and is inherited by all of the access classes 3 3 2 Database Class PgDatabase The database class provides C objects that have a connec
399. xceptions 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 list fields fieldname and fieldnum methods 149 dictresult Name dictresult like getresult but returns 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 dictionary with the field names used as the dictionary index 150 listfields Name listfields lists 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 151 fieldname Name fieldname field number name conversion 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
400. xec creates an execution plan parser planner optimizer and executes the query for t count 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 tcount 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 the last query was executed is returned in the global variable SPI_processed if not SPI_LOK_UTILITY If SPILOK_SELECT is returned and SPI_processed gt 0 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_LERROR_UNCONNECTED if procedure is unconnected SPI_LERROR_COPY if COPY TO FROM stdin SPI_LERROR_CURSOR if DECLARE CLOSE CURSOR FETCH SPI_ERROR_TRANSACTION if BEGIN ABORT END SPI_LERROR_OPUNKNOWN if type of query is unknown this shouldn t occur Structures If SPI_OK_SELECT is returned and SPI_processe
401. y 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 Libpq libpq 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 large 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 2 3 4 Opening an Existing Large Object To open a
402. y not be what you want The language module translates Python s None into SQL NULL PostgreSQL function variables are available in the global args list In the my func 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 backend 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 mentioned above When a function is used in a trigger the dictionary TD contains transaction related values The trigger tuples 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 Or UNKNOWN TD level contains one of ROW STATEMENT or 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 trigger when
403. y 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 in curs 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 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 23 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 23 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 have less development costs 23 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 e Using a text editor and reloading the file with psql 291 Chapter 23 PL pgSQL
404. yntaxError 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 118 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 envi ronment variables will be used in future connections It returns the previous setting for default port 119 get_defopt Name get_defopt get default options specification DV Synopsis get_defopt Parameters none Return Type string or None Default options specification Exceptions SyntaxError Too many arguments Description get_defopt returns the current default connection options specification or None if the environ ment variables should be used Environment variables will not be looked up 120 set_defopt Name set_defopt set 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 t
405. ype 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 121 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 variables should be used Environment variables will not be looked up 122 set_deftty Name set_deftty set default debug terminal specification DV Synopsis set_deftty terminal Parameters terminal New default debug terminal string None Return 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 environment variables will be used in future connections It returns the previous setting for default terminal 123 get_defbase Name get_defbase get default database name specification DV Synopsis get_defbase Parameters none Return Type string o
406. ype 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 constants 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 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 252 SPI_prepare If the query uses parameters their number and datatypes 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_savep1lan to save a plan for longer If successful a non null pointer will be returned Otherwise you ll get a NULL p
407. ype 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 upto 1Gig 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 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 get Bytes setBytes getBinaryStream and setBinaryStream operate on the bytea data type In 7 1 these methods operated on the OID data type associated with Large 88 Chapter 8 JDBC Interface Objects It is possi
408. ypoutput typrecelve 4 typsend aN D N pg_am lj 1 Laid o amgettuple aminsert amdelete am getattr ambeginsean KEY AITITeScan DEPENDENT endam areign key ammarkpos Chapter 11 Extending SQL An Overview The Developer s Guide gives a more detailed explanation of these catalogs and their columns How ever Figure 11 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 should 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 inte grated 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 contai
409. zes 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 In order to manage diverse support routines consistently across all PostgreSQL access methods pg_am includes a column called amsupport This column records the number of support routines used by an access method For B trees this number is one the routine to take two keys and return 1 0 or 1 depending on whether the first key is less than equal to or greater than the second Strictly speaking this routine can return a negative number lt 0 zero or a non zero positive number gt 0 The amstrategies entry in pg_am is just the number of strategies defined for the access method in question The operators for less than less equal and so on don t appear in pg_am Similarly amsupport is just the number of support routines required by the access method The actual routines are listed elsewhere By the way the amorderstrategy column tells whether the access method supports ordered scan Zero means it doesn t if it does anorderstrategy is the number of the strategy routine that corre sponds to the ordering operator For example B tree has amorderstrategy 1 which is its less than strategy number 17 5 Operator Classes The next table of interest is pg_opclass This table defines operator class names and input data types for each of the operato

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