<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >SPI_prepare</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 8.0.11 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Interface Functions" HREF="spi.html#SPI-INTERFACE"><LINK REL="PREVIOUS" TITLE="SPI_exec" HREF="spi-spi-exec.html"><LINK REL="NEXT" TITLE="SPI_getargcount" HREF="spi-spi-getargcount.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="2007-02-02T03:57:22"></HEAD ><BODY CLASS="REFENTRY" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.0.11 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="spi-spi-exec.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="spi-spi-exec.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="spi-spi-getargcount.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="spi-spi-getargcount.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="SPI-SPI-PREPARE" ></A >SPI_prepare</H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN34902" ></A ><H2 >Name</H2 >SPI_prepare -- prepare a plan for a command, without executing it yet</DIV ><A NAME="AEN34905" ></A ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN34907" ></A ><H2 >Synopsis</H2 ><PRE CLASS="SYNOPSIS" >void * SPI_prepare(const char * <TT CLASS="PARAMETER" >command</TT >, int <TT CLASS="PARAMETER" >nargs</TT >, Oid * <TT CLASS="PARAMETER" >argtypes</TT >)</PRE ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN34912" ></A ><H2 >Description</H2 ><P > <CODE CLASS="FUNCTION" >SPI_prepare</CODE > creates and returns an execution plan for the specified command but doesn't execute the command. This function should only be called from a connected procedure. </P ><P > When the same or a similar command is to be executed repeatedly, it may be advantageous to perform the planning only once. <CODE CLASS="FUNCTION" >SPI_prepare</CODE > converts a command string into an execution plan that can be executed repeatedly using <CODE CLASS="FUNCTION" >SPI_execute_plan</CODE >. </P ><P > A prepared command can be generalized by writing parameters (<TT CLASS="LITERAL" >$1</TT >, <TT CLASS="LITERAL" >$2</TT >, etc.) in place of what would be constants in a normal command. The actual values of the parameters are then specified when <CODE CLASS="FUNCTION" >SPI_execute_plan</CODE > is called. This allows the prepared command to be used over a wider range of situations than would be possible without parameters. </P ><P > The plan returned by <CODE CLASS="FUNCTION" >SPI_prepare</CODE > can be used only in the current invocation of the procedure, since <CODE CLASS="FUNCTION" >SPI_finish</CODE > frees memory allocated for a plan. But a plan can be saved for longer using the function <CODE CLASS="FUNCTION" >SPI_saveplan</CODE >. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN34927" ></A ><H2 >Arguments</H2 ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT ><TT CLASS="LITERAL" >const char * <TT CLASS="PARAMETER" >command</TT ></TT ></DT ><DD ><P > command string </P ></DD ><DT ><TT CLASS="LITERAL" >int <TT CLASS="PARAMETER" >nargs</TT ></TT ></DT ><DD ><P > number of input parameters (<TT CLASS="LITERAL" >$1</TT >, <TT CLASS="LITERAL" >$2</TT >, etc.) </P ></DD ><DT ><TT CLASS="LITERAL" >Oid * <TT CLASS="PARAMETER" >argtypes</TT ></TT ></DT ><DD ><P > pointer to an array containing the <ACRONYM CLASS="ACRONYM" >OID</ACRONYM >s of the data types of the parameters </P ></DD ></DL ></DIV ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN34951" ></A ><H2 >Return Value</H2 ><P > <CODE CLASS="FUNCTION" >SPI_prepare</CODE > returns a non-null pointer to an execution plan. On error, <TT CLASS="SYMBOL" >NULL</TT > will be returned, and <TT CLASS="VARNAME" >SPI_result</TT > will be set to one of the same error codes used by <CODE CLASS="FUNCTION" >SPI_execute</CODE >, except that it is set to <TT CLASS="SYMBOL" >SPI_ERROR_ARGUMENT</TT > if <TT CLASS="PARAMETER" >command</TT > is <TT CLASS="SYMBOL" >NULL</TT >, or if <TT CLASS="PARAMETER" >nargs</TT > is less than 0, or if <TT CLASS="PARAMETER" >nargs</TT > is greater than 0 and <TT CLASS="PARAMETER" >argtypes</TT > is <TT CLASS="SYMBOL" >NULL</TT >. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN34965" ></A ><H2 >Notes</H2 ><P > There is a disadvantage to using parameters: since the planner does not know the values that will be supplied for the parameters, it may make worse planning choices than it would make for a normal command with all constants visible. </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-spi-exec.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="spi-spi-getargcount.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SPI_exec</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="spi.html#SPI-INTERFACE" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >SPI_getargcount</TD ></TR ></TABLE ></DIV ></BODY ></HTML >