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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>11.11. Indexes and Collations</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-opclass.html" title="11.10. Operator Classes and Operator Families" /><link rel="next" href="indexes-examine.html" title="11.12. Examining Index Usage" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">11.11. Indexes and Collations</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="indexes-opclass.html" title="11.10. Operator Classes and Operator Families">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 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="indexes-examine.html" title="11.12. Examining Index Usage">Next</a></td></tr></table><hr /></div><div class="sect1" id="INDEXES-COLLATIONS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">11.11. Indexes and Collations</h2></div></div></div><p>
+   An index can support only one collation per index column.
+   If multiple collations are of interest, multiple indexes may be needed.
+  </p><p>
+   Consider these statements:
+</p><pre class="programlisting">
+CREATE TABLE test1c (
+    id integer,
+    content varchar COLLATE "x"
+);
+
+CREATE INDEX test1c_content_index ON test1c (content);
+</pre><p>
+   The index automatically uses the collation of the
+   underlying column.  So a query of the form
+</p><pre class="programlisting">
+SELECT * FROM test1c WHERE content &gt; <em class="replaceable"><code>constant</code></em>;
+</pre><p>
+   could use the index, because the comparison will by default use the
+   collation of the column.  However, this index cannot accelerate queries
+   that involve some other collation.  So if queries of the form, say,
+</p><pre class="programlisting">
+SELECT * FROM test1c WHERE content &gt; <em class="replaceable"><code>constant</code></em> COLLATE "y";
+</pre><p>
+   are also of interest, an additional index could be created that supports
+   the <code class="literal">"y"</code> collation, like this:
+</p><pre class="programlisting">
+CREATE INDEX test1c_content_y_index ON test1c (content COLLATE "y");
+</pre><p>
+  </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="indexes-opclass.html" title="11.10. Operator Classes and Operator Families">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-examine.html" title="11.12. Examining Index Usage">Next</a></td></tr><tr><td width="40%" align="left" valign="top">11.10. Operator Classes and Operator Families </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 11.12. Examining Index Usage</td></tr></table></div></body></html>
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