<!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 9.6.19 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Interface Functions" HREF="spi-interface.html"><LINK REL="PREVIOUS" TITLE="SPI_execute_with_args" HREF="spi-spi-execute-with-args.html"><LINK REL="NEXT" TITLE="SPI_prepare_cursor" HREF="spi-spi-prepare-cursor.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="2020-09-02T07:27:19"></HEAD ><BODY CLASS="REFENTRY" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="4" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.6.19 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="SPI_execute_with_args" HREF="spi-spi-execute-with-args.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="spi-interface.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="SPI_prepare_cursor" HREF="spi-spi-prepare-cursor.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="AEN70213" ></A ><H2 >Name</H2 >SPI_prepare -- prepare a statement, without executing it yet</DIV ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN70216" ></A ><H2 >Synopsis</H2 ><PRE CLASS="SYNOPSIS" >SPIPlanPtr 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="AEN70221" ></A ><H2 >Description</H2 ><P > <CODE CLASS="FUNCTION" >SPI_prepare</CODE > creates and returns a prepared statement for the specified command, but doesn't execute the command. The prepared statement can later be executed repeatedly using <CODE CLASS="FUNCTION" >SPI_execute_plan</CODE >. </P ><P > When the same or a similar command is to be executed repeatedly, it is generally advantageous to perform parse analysis only once, and might furthermore be advantageous to re-use an execution plan for the command. <CODE CLASS="FUNCTION" >SPI_prepare</CODE > converts a command string into a prepared statement that encapsulates the results of parse analysis. The prepared statement also provides a place for caching an execution plan if it is found that generating a custom plan for each execution is not helpful. </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 statement 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 such a statement. But the statement can be saved for longer using the functions <CODE CLASS="FUNCTION" >SPI_keepplan</CODE > or <CODE CLASS="FUNCTION" >SPI_saveplan</CODE >. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN70237" ></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="AEN70261" ></A ><H2 >Return Value</H2 ><P > <CODE CLASS="FUNCTION" >SPI_prepare</CODE > returns a non-null pointer to an <TT CLASS="TYPE" >SPIPlan</TT >, which is an opaque struct representing a prepared statement. 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="AEN70276" ></A ><H2 >Notes</H2 ><P > If no parameters are defined, a generic plan will be created at the first use of <CODE CLASS="FUNCTION" >SPI_execute_plan</CODE >, and used for all subsequent executions as well. If there are parameters, the first few uses of <CODE CLASS="FUNCTION" >SPI_execute_plan</CODE > will generate custom plans that are specific to the supplied parameter values. After enough uses of the same prepared statement, <CODE CLASS="FUNCTION" >SPI_execute_plan</CODE > will build a generic plan, and if that is not too much more expensive than the custom plans, it will start using the generic plan instead of re-planning each time. If this default behavior is unsuitable, you can alter it by passing the <TT CLASS="LITERAL" >CURSOR_OPT_GENERIC_PLAN</TT > or <TT CLASS="LITERAL" >CURSOR_OPT_CUSTOM_PLAN</TT > flag to <CODE CLASS="FUNCTION" >SPI_prepare_cursor</CODE >, to force use of generic or custom plans respectively. </P ><P > Although the main point of a prepared statement is to avoid repeated parse analysis and planning of the statement, <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > will force re-analysis and re-planning of the statement before using it whenever database objects used in the statement have undergone definitional (DDL) changes since the previous use of the prepared statement. Also, if the value of <A HREF="runtime-config-client.html#GUC-SEARCH-PATH" >search_path</A > changes from one use to the next, the statement will be re-parsed using the new <TT CLASS="VARNAME" >search_path</TT >. (This latter behavior is new as of <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > 9.3.) See <A HREF="sql-prepare.html" >PREPARE</A > for more information about the behavior of prepared statements. </P ><P > This function should only be called from a connected procedure. </P ><P > <TT CLASS="TYPE" >SPIPlanPtr</TT > is declared as a pointer to an opaque struct type in <TT CLASS="FILENAME" >spi.h</TT >. It is unwise to try to access its contents directly, as that makes your code much more likely to break in future revisions of <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >. </P ><P > The name <TT CLASS="TYPE" >SPIPlanPtr</TT > is somewhat historical, since the data structure no longer necessarily contains an execution plan. </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-execute-with-args.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-prepare-cursor.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SPI_execute_with_args</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="spi-interface.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >SPI_prepare_cursor</TD ></TR ></TABLE ></DIV ></BODY ></HTML >