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<?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>11.1. Introduction</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="indexes.html" title="Chapter 11. Indexes" /><link rel="next" href="indexes-types.html" title="11.2. Index Types" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">11.1. Introduction</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="indexes.html" title="Chapter 11. Indexes">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="indexes.html" title="Chapter 11. Indexes">Up</a></td><th width="60%" align="center">Chapter 11. Indexes</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="indexes-types.html" title="11.2. Index Types">Next</a></td></tr></table><hr /></div><div class="sect1" id="INDEXES-INTRO"><div class="titlepage"><div><div><h2 class="title" style="clear: both">11.1. Introduction</h2></div></div></div><p>
+<!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>11.1. Introduction</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="indexes.html" title="Chapter 11. Indexes" /><link rel="next" href="indexes-types.html" title="11.2. Index Types" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">11.1. Introduction</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="indexes.html" title="Chapter 11. Indexes">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="indexes.html" title="Chapter 11. Indexes">Up</a></td><th width="60%" align="center">Chapter 11. Indexes</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="indexes-types.html" title="11.2. Index Types">Next</a></td></tr></table><hr /></div><div class="sect1" id="INDEXES-INTRO"><div class="titlepage"><div><div><h2 class="title" style="clear: both">11.1. Introduction</h2></div></div></div><p>
Suppose we have a table similar to this:
</p><pre class="programlisting">
CREATE TABLE test1 (
@@ -59,6 +59,35 @@ CREATE INDEX test1_id_index ON test1 (id);
an index defined on a column that is part of a join condition can
also significantly speed up queries with joins.
</p><p>
+ In general, <span class="productname">PostgreSQL</span> indexes can be used
+ to optimize queries that contain one or more <code class="literal">WHERE</code>
+ or <code class="literal">JOIN</code> clauses of the form
+
+</p><pre class="synopsis">
+<em class="replaceable"><code>indexed-column</code></em> <em class="replaceable"><code>indexable-operator</code></em> <em class="replaceable"><code>comparison-value</code></em>
+</pre><p>
+
+ Here, the <em class="replaceable"><code>indexed-column</code></em> is whatever
+ column or expression the index has been defined on.
+ The <em class="replaceable"><code>indexable-operator</code></em> is an operator that
+ is a member of the index's <em class="firstterm">operator class</em> for
+ the indexed column. (More details about that appear below.)
+ And the <em class="replaceable"><code>comparison-value</code></em> can be any
+ expression that is not volatile and does not reference the index's
+ table.
+ </p><p>
+ In some cases the query planner can extract an indexable clause of
+ this form from another SQL construct. A simple example is that if
+ the original clause was
+
+</p><pre class="synopsis">
+<em class="replaceable"><code>comparison-value</code></em> <em class="replaceable"><code>operator</code></em> <em class="replaceable"><code>indexed-column</code></em>
+</pre><p>
+
+ then it can be flipped around into indexable form if the
+ original <em class="replaceable"><code>operator</code></em> has a commutator
+ operator that is a member of the index's operator class.
+ </p><p>
Creating an index on a large table can take a long time. By default,
<span class="productname">PostgreSQL</span> allows reads (<code class="command">SELECT</code> statements) to occur
on the table in parallel with index creation, but writes (<code class="command">INSERT</code>,
@@ -74,4 +103,4 @@ CREATE INDEX test1_id_index ON test1 (id);
tuples</a>.
Therefore indexes that are seldom or never used in queries
should be removed.
- </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="indexes.html" title="Chapter 11. Indexes">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="indexes.html" title="Chapter 11. Indexes">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="indexes-types.html" title="11.2. Index Types">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 11. Indexes </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 11.2. Index Types</td></tr></table></div></body></html> \ No newline at end of file
+ </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="indexes.html" title="Chapter 11. Indexes">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="indexes.html" title="Chapter 11. Indexes">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="indexes-types.html" title="11.2. Index Types">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 11. Indexes </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 11.2. Index Types</td></tr></table></div></body></html> \ No newline at end of file