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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Examples</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Server Programming Interface" HREF="spi.html"><LINK REL="PREVIOUS" TITLE="Visibility of Data Changes" HREF="spi-visibility.html"><LINK REL="NEXT" TITLE="Reference" HREF="reference.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Visibility of Data Changes" HREF="spi-visibility.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="spi.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 43. Server Programming Interface</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Reference" HREF="reference.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="SPI-EXAMPLES" >43.5. Examples</A ></H1 ><P > This section contains a very simple example of SPI usage. The procedure <CODE CLASS="FUNCTION" >execq</CODE > takes an SQL command as its first argument and a row count as its second, executes the command using <CODE CLASS="FUNCTION" >SPI_exec</CODE > and returns the number of rows that were processed by the command. You can find more complex examples for SPI in the source tree in <TT CLASS="FILENAME" >src/test/regress/regress.c</TT > and in the <A HREF="contrib-spi.html" >spi</A > module. </P ><PRE CLASS="PROGRAMLISTING" >#include "postgres.h" #include "executor/spi.h" #include "utils/builtins.h" #ifdef PG_MODULE_MAGIC PG_MODULE_MAGIC; #endif int execq(text *sql, int cnt); int execq(text *sql, int cnt) { char *command; int ret; int proc; /* Convert given text object to a C string */ command = text_to_cstring(sql); SPI_connect(); ret = SPI_exec(command, cnt); proc = SPI_processed; /* * If some rows were fetched, print them via elog(INFO). */ if (ret > 0 && SPI_tuptable != NULL) { TupleDesc tupdesc = SPI_tuptable->tupdesc; SPITupleTable *tuptable = SPI_tuptable; char buf[8192]; int i, j; for (j = 0; j < proc; j++) { HeapTuple tuple = tuptable->vals[j]; for (i = 1, buf[0] = 0; i <= tupdesc->natts; i++) snprintf(buf + strlen (buf), sizeof(buf) - strlen(buf), " %s%s", SPI_getvalue(tuple, tupdesc, i), (i == tupdesc->natts) ? " " : " |"); elog(INFO, "EXECQ: %s", buf); } } SPI_finish(); pfree(command); return (proc); }</PRE ><P > (This function uses call convention version 0, to make the example easier to understand. In real applications you should use the new version 1 interface.) </P ><P > This is how you declare the function after having compiled it into a shared library (details are in <A HREF="xfunc-c.html#DFUNC" >Section 35.9.6</A >.): </P><PRE CLASS="PROGRAMLISTING" >CREATE FUNCTION execq(text, integer) RETURNS integer AS '<TT CLASS="REPLACEABLE" ><I >filename</I ></TT >' LANGUAGE C;</PRE ><P> </P ><P > Here is a sample session: </P><PRE CLASS="PROGRAMLISTING" >=> SELECT execq('CREATE TABLE a (x integer)', 0); execq ------- 0 (1 row) => INSERT INTO a VALUES (execq('INSERT INTO a VALUES (0)', 0)); INSERT 0 1 => SELECT execq('SELECT * FROM a', 0); INFO: EXECQ: 0 -- inserted by execq INFO: EXECQ: 1 -- returned by execq and inserted by upper INSERT execq ------- 2 (1 row) => SELECT execq('INSERT INTO a SELECT x + 2 FROM a', 1); execq ------- 1 (1 row) => SELECT execq('SELECT * FROM a', 10); INFO: EXECQ: 0 INFO: EXECQ: 1 INFO: EXECQ: 2 -- 0 + 2, only one row inserted - as specified execq ------- 3 -- 10 is the max value only, 3 is the real number of rows (1 row) => DELETE FROM a; DELETE 3 => INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1); INSERT 0 1 => SELECT * FROM a; x --- 1 -- no rows in a (0) + 1 (1 row) => INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1); INFO: EXECQ: 1 INSERT 0 1 => SELECT * FROM a; x --- 1 2 -- there was one row in a + 1 (2 rows) -- This demonstrates the data changes visibility rule: => INSERT INTO a SELECT execq('SELECT * FROM a', 0) * x FROM a; INFO: EXECQ: 1 INFO: EXECQ: 2 INFO: EXECQ: 1 INFO: EXECQ: 2 INFO: EXECQ: 2 INSERT 0 2 => SELECT * FROM a; x --- 1 2 2 -- 2 rows * 1 (x in first row) 6 -- 3 rows (2 + 1 just inserted) * 2 (x in second row) (4 rows) ^^^^^^ rows visible to execq() in different invocations</PRE ><P> </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="spi-visibility.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="reference.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Visibility of Data Changes</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="spi.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Reference</TD ></TR ></TABLE ></DIV ></BODY ></HTML >