| Server IP : 104.21.25.180 / Your IP : 104.23.197.123 Web Server : Apache/2.4.37 System : Linux almalinux.duckdns.org 4.18.0-553.111.1.el8_10.x86_64 #1 SMP Sun Mar 8 20:06:07 EDT 2026 x86_64 User : ricodeal ( 1046) PHP Version : 7.4.33 Disable Function : NONE MySQL : OFF | cURL : ON | WGET : ON | Perl : ON | Python : ON | Sudo : ON | Pkexec : ON Directory : /usr/share/doc/postgresql-docs/html/ |
Upload File : |
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!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>42.4. Expressions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="[email protected]" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="plpgsql-declarations.html" title="42.3. Declarations" /><link rel="next" href="plpgsql-statements.html" title="42.5. Basic Statements" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">42.4. Expressions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpgsql-declarations.html" title="42.3. Declarations">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plpgsql.html" title="Chapter 42. PL/pgSQL - SQL Procedural Language">Up</a></td><th width="60%" align="center">Chapter 42. <span xmlns="http://www.w3.org/1999/xhtml" class="application">PL/pgSQL</span> - <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym> Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 10.23 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpgsql-statements.html" title="42.5. Basic Statements">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPGSQL-EXPRESSIONS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">42.4. Expressions</h2></div></div></div><p> All expressions used in <span class="application">PL/pgSQL</span>
statements are processed using the server's main
<acronym class="acronym">SQL</acronym> executor. For example, when you write
a <span class="application">PL/pgSQL</span> statement like
</p><pre class="synopsis">IF <em class="replaceable"><code>expression</code></em> THEN ...</pre><p>
<span class="application">PL/pgSQL</span> will evaluate the expression by
feeding a query like
</p><pre class="synopsis">SELECT <em class="replaceable"><code>expression</code></em></pre><p>
to the main SQL engine. While forming the <code class="command">SELECT</code> command,
any occurrences of <span class="application">PL/pgSQL</span> variable names
are replaced by parameters, as discussed in detail in
<a class="xref" href="plpgsql-implementation.html#PLPGSQL-VAR-SUBST" title="42.10.1. Variable Substitution">Section 42.10.1</a>.
This allows the query plan for the <code class="command">SELECT</code> to
be prepared just once and then reused for subsequent
evaluations with different values of the variables. Thus, what
really happens on first use of an expression is essentially a
<code class="command">PREPARE</code> command. For example, if we have declared
two integer variables <code class="literal">x</code> and <code class="literal">y</code>, and we write
</p><pre class="programlisting">IF x < y THEN ...</pre><p>
what happens behind the scenes is equivalent to
</p><pre class="programlisting">PREPARE <em class="replaceable"><code>statement_name</code></em>(integer, integer) AS SELECT $1 < $2;</pre><p>
and then this prepared statement is <code class="command">EXECUTE</code>d for each
execution of the <code class="command">IF</code> statement, with the current values
of the <span class="application">PL/pgSQL</span> variables supplied as
parameter values. Normally these details are
not important to a <span class="application">PL/pgSQL</span> user, but
they are useful to know when trying to diagnose a problem.
More information appears in <a class="xref" href="plpgsql-implementation.html#PLPGSQL-PLAN-CACHING" title="42.10.2. Plan Caching">Section 42.10.2</a>.
</p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpgsql-declarations.html" title="42.3. Declarations">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plpgsql.html" title="Chapter 42. PL/pgSQL - SQL Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpgsql-statements.html" title="42.5. Basic Statements">Next</a></td></tr><tr><td width="40%" align="left" valign="top">42.3. Declarations </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 10.23 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 42.5. Basic Statements</td></tr></table></div></body></html>