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<!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>Chapter 41. The Rule System</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="event-trigger-table-rewrite-example.html" title="40.5. A Table Rewrite Event Trigger Example" /><link rel="next" href="querytree.html" title="41.1. The Query Tree" /></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">Chapter 41. The Rule System</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="event-trigger-table-rewrite-example.html" title="40.5. A Table Rewrite Event Trigger Example">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="server-programming.html" title="Part V. Server Programming">Up</a></td><th width="60%" align="center">Part V. Server Programming</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="querytree.html" title="41.1. The Query Tree">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="RULES"><div class="titlepage"><div><div><h2 class="title">Chapter 41. The Rule System</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="querytree.html">41.1. The Query Tree</a></span></dt><dt><span class="sect1"><a href="rules-views.html">41.2. Views and the Rule System</a></span></dt><dd><dl><dt><span class="sect2"><a href="rules-views.html#RULES-SELECT">41.2.1. How <code class="command">SELECT</code> Rules Work</a></span></dt><dt><span class="sect2"><a href="rules-views.html#id-1.8.6.7.6">41.2.2. View Rules in Non-<code class="command">SELECT</code> Statements</a></span></dt><dt><span class="sect2"><a href="rules-views.html#id-1.8.6.7.7">41.2.3. The Power of Views in <span class="productname">PostgreSQL</span></a></span></dt><dt><span class="sect2"><a href="rules-views.html#RULES-VIEWS-UPDATE">41.2.4. Updating a View</a></span></dt></dl></dd><dt><span class="sect1"><a href="rules-materializedviews.html">41.3. Materialized Views</a></span></dt><dt><span class="sect1"><a href="rules-update.html">41.4. Rules on <code class="command">INSERT</code>, <code class="command">UPDATE</code>, and <code class="command">DELETE</code></a></span></dt><dd><dl><dt><span class="sect2"><a href="rules-update.html#id-1.8.6.9.7">41.4.1. How Update Rules Work</a></span></dt><dt><span class="sect2"><a href="rules-update.html#RULES-UPDATE-VIEWS">41.4.2. Cooperation with Views</a></span></dt></dl></dd><dt><span class="sect1"><a href="rules-privileges.html">41.5. Rules and Privileges</a></span></dt><dt><span class="sect1"><a href="rules-status.html">41.6. Rules and Command Status</a></span></dt><dt><span class="sect1"><a href="rules-triggers.html">41.7. Rules Versus Triggers</a></span></dt></dl></div><a id="id-1.8.6.2" class="indexterm"></a><p>
This chapter discusses the rule system in
<span class="productname">PostgreSQL</span>. Production rule systems
are conceptually simple, but there are many subtle points
involved in actually using them.
</p><p>
Some other database systems define active database rules, which
are usually stored procedures and triggers. In
<span class="productname">PostgreSQL</span>, these can be implemented
using functions and triggers as well.
</p><p>
The rule system (more precisely speaking, the query rewrite rule
system) is totally different from stored procedures and triggers.
It modifies queries to take rules into consideration, and then
passes the modified query to the query planner for planning and
execution. It is very powerful, and can be used for many things
such as query language procedures, views, and versions. The
theoretical foundations and the power of this rule system are
also discussed in <a class="xref" href="biblio.html#STON90B">[ston90b]</a> and <a class="xref" href="biblio.html#ONG90">[ong90]</a>.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="event-trigger-table-rewrite-example.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="server-programming.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="querytree.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">40.5. A Table Rewrite Event Trigger Example </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 41.1. The Query Tree</td></tr></table></div></body></html>
