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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="spi-spi-prepare"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>SPI_prepare — prepare a plan for a command, without executing it yet</p>
</div>
<a name="id735240"></a><div class="refsynopsisdiv">
<h2>Synopsis</h2>
<pre class="synopsis">void * 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>)</pre>
</div>
<div class="refsect1" lang="en">
<a name="id735273"></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
(<code class="literal">$1</code>, <code class="literal">$2</code>, 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" lang="en">
<a name="id735362"></a><h2>Arguments</h2>
<div class="variablelist"><dl>
<dt><span class="term"><code class="literal">const char * <em class="parameter"><code>command</code></em></code></span></dt>
<dd><p> command string
</p></dd>
<dt><span class="term"><code class="literal">int <em class="parameter"><code>nargs</code></em></code></span></dt>
<dd><p> number of input parameters (<code class="literal">$1</code>, <code class="literal">$2</code>, etc.)
</p></dd>
<dt><span class="term"><code class="literal">Oid * <em class="parameter"><code>argtypes</code></em></code></span></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" lang="en">
<a name="id735435"></a><h2>Return Value</h2>
<p> <code class="function">SPI_prepare</code> returns a non-null pointer to an
execution plan. On error, <code class="symbol">NULL</code> will be returned,
and <code class="varname">SPI_result</code> will be set to one of the same
error codes used by <code class="function">SPI_execute</code>, except that
it is set to <code class="symbol">SPI_ERROR_ARGUMENT</code> if
<em class="parameter"><code>command</code></em> is <code class="symbol">NULL</code>, or if
<em class="parameter"><code>nargs</code></em> is less than 0, or if <em class="parameter"><code>nargs</code></em> is
greater than 0 and <em class="parameter"><code>argtypes</code></em> is <code class="symbol">NULL</code>.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id735506"></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>
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