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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 V1.79.1" /><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><div xmlns="http://www.w3.org/TR/xhtml1/transitional" 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 12.4 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></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 > <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 > <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>
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