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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>SPI_prepare</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="spi-spi-execute-with-args.html" title="SPI_execute_with_args" /><link rel="next" href="spi-spi-prepare-cursor.html" title="SPI_prepare_cursor" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">SPI_prepare</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="spi-spi-execute-with-args.html" title="SPI_execute_with_args">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="spi-interface.html" title="47.1. Interface Functions">Up</a></td><th width="60%" align="center">47.1. Interface Functions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="spi-spi-prepare-cursor.html" title="SPI_prepare_cursor">Next</a></td></tr></table><hr /></div><div class="refentry" id="SPI-SPI-PREPARE"><div class="titlepage"></div><a id="id-1.8.12.8.8.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">SPI_prepare</span></h2><p>SPI_prepare — prepare a statement, without executing it yet</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">3SPIPlanPtr SPI_prepare(const char * <em class="parameter"><code>command</code></em>, int <em class="parameter"><code>nargs</code></em>, Oid * <em class="parameter"><code>argtypes</code></em>)4</pre></div><div class="refsect1" id="id-1.8.12.8.8.5"><h2>Description</h2><p>5   <code class="function">SPI_prepare</code> creates and returns a prepared6   statement for the specified command, but doesn't execute the command.7   The prepared statement can later be executed repeatedly using8   <code class="function">SPI_execute_plan</code>.9  </p><p>10   When the same or a similar command is to be executed repeatedly, it11   is generally advantageous to perform parse analysis only once, and12   might furthermore be advantageous to re-use an execution plan for the13   command.14   <code class="function">SPI_prepare</code> converts a command string into a15   prepared statement that encapsulates the results of parse analysis.16   The prepared statement also provides a place for caching an execution plan17   if it is found that generating a custom plan for each execution is not18   helpful.19  </p><p>20   A prepared command can be generalized by writing parameters21   (<code class="literal">$1</code>, <code class="literal">$2</code>, etc.) in place of what would be22   constants in a normal command.  The actual values of the parameters23   are then specified when <code class="function">SPI_execute_plan</code> is called.24   This allows the prepared command to be used over a wider range of25   situations than would be possible without parameters.26  </p><p>27   The statement returned by <code class="function">SPI_prepare</code> can be used28   only in the current invocation of the C function, since29   <code class="function">SPI_finish</code> frees memory allocated for such a30   statement.  But the statement can be saved for longer using the functions31   <code class="function">SPI_keepplan</code> or <code class="function">SPI_saveplan</code>.32  </p></div><div class="refsect1" id="id-1.8.12.8.8.6"><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">const char * <em class="parameter"><code>command</code></em></code></span></dt><dd><p>33      command string34     </p></dd><dt><span class="term"><code class="literal">int <em class="parameter"><code>nargs</code></em></code></span></dt><dd><p>35      number of input parameters (<code class="literal">$1</code>, <code class="literal">$2</code>, etc.)36     </p></dd><dt><span class="term"><code class="literal">Oid * <em class="parameter"><code>argtypes</code></em></code></span></dt><dd><p>37      pointer to an array containing the <acronym class="acronym">OID</acronym>s of38      the data types of the parameters39     </p></dd></dl></div></div><div class="refsect1" id="id-1.8.12.8.8.7"><h2>Return Value</h2><p>40   <code class="function">SPI_prepare</code> returns a non-null pointer to an41   <code class="type">SPIPlan</code>, which is an opaque struct representing a prepared42   statement.  On error, <code class="symbol">NULL</code> will be returned,43   and <code class="varname">SPI_result</code> will be set to one of the same44   error codes used by <code class="function">SPI_execute</code>, except that45   it is set to <code class="symbol">SPI_ERROR_ARGUMENT</code> if46   <em class="parameter"><code>command</code></em> is <code class="symbol">NULL</code>, or if47   <em class="parameter"><code>nargs</code></em> is less than 0, or if <em class="parameter"><code>nargs</code></em> is48   greater than 0 and <em class="parameter"><code>argtypes</code></em> is <code class="symbol">NULL</code>.49  </p></div><div class="refsect1" id="id-1.8.12.8.8.8"><h2>Notes</h2><p>50   If no parameters are defined, a generic plan will be created at the51   first use of <code class="function">SPI_execute_plan</code>, and used for all52   subsequent executions as well.  If there are parameters, the first few uses53   of <code class="function">SPI_execute_plan</code> will generate custom plans54   that are specific to the supplied parameter values.  After enough uses55   of the same prepared statement, <code class="function">SPI_execute_plan</code> will56   build a generic plan, and if that is not too much more expensive than the57   custom plans, it will start using the generic plan instead of re-planning58   each time.  If this default behavior is unsuitable, you can alter it by59   passing the <code class="literal">CURSOR_OPT_GENERIC_PLAN</code> or60   <code class="literal">CURSOR_OPT_CUSTOM_PLAN</code> flag to61   <code class="function">SPI_prepare_cursor</code>, to force use of generic or custom62   plans respectively.63  </p><p>64   Although the main point of a prepared statement is to avoid repeated parse65   analysis and planning of the statement, <span class="productname">PostgreSQL</span> will66   force re-analysis and re-planning of the statement before using it67   whenever database objects used in the statement have undergone68   definitional (DDL) changes since the previous use of the prepared69   statement.  Also, if the value of <a class="xref" href="runtime-config-client.html#GUC-SEARCH-PATH">search_path</a> changes70   from one use to the next, the statement will be re-parsed using the new71   <code class="varname">search_path</code>.  (This latter behavior is new as of72   <span class="productname">PostgreSQL</span> 9.3.)  See <a class="xref" href="sql-prepare.html" title="PREPARE"><span class="refentrytitle">PREPARE</span></a> for more information about the behavior of prepared73   statements.74  </p><p>75   This function should only be called from a connected C function.76  </p><p>77   <code class="type">SPIPlanPtr</code> is declared as a pointer to an opaque struct type in78   <code class="filename">spi.h</code>.  It is unwise to try to access its contents79   directly, as that makes your code much more likely to break in80   future revisions of <span class="productname">PostgreSQL</span>.81  </p><p>82   The name <code class="type">SPIPlanPtr</code> is somewhat historical, since the data83   structure no longer necessarily contains an execution plan.84  </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="spi-spi-execute-with-args.html" title="SPI_execute_with_args">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="spi-interface.html" title="47.1. Interface Functions">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="spi-spi-prepare-cursor.html" title="SPI_prepare_cursor">Next</a></td></tr><tr><td width="40%" align="left" valign="top">SPI_execute_with_args </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> SPI_prepare_cursor</td></tr></table></div></body></html>