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diff --git a/doc/src/sgml/html/indexes-opclass.html b/doc/src/sgml/html/indexes-opclass.html new file mode 100644 index 0000000..0ed4caf --- /dev/null +++ b/doc/src/sgml/html/indexes-opclass.html @@ -0,0 +1,107 @@ +<?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>11.10. Operator Classes and Operator Families</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-index-only-scans.html" title="11.9. Index-Only Scans and Covering Indexes" /><link rel="next" href="indexes-collations.html" title="11.11. Indexes and Collations" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">11.10. Operator Classes and Operator Families</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="indexes-index-only-scans.html" title="11.9. Index-Only Scans and Covering 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 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="indexes-collations.html" title="11.11. Indexes and Collations">Next</a></td></tr></table><hr /></div><div class="sect1" id="INDEXES-OPCLASS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">11.10. Operator Classes and Operator Families</h2></div></div></div><a id="id-1.5.10.13.2" class="indexterm"></a><a id="id-1.5.10.13.3" class="indexterm"></a><p> + An index definition can specify an <em class="firstterm">operator + class</em> for each column of an index. +</p><pre class="synopsis"> +CREATE INDEX <em class="replaceable"><code>name</code></em> ON <em class="replaceable"><code>table</code></em> (<em class="replaceable"><code>column</code></em> <em class="replaceable"><code>opclass</code></em> [ ( <em class="replaceable"><code>opclass_options</code></em> ) ] [<span class="optional"><em class="replaceable"><code>sort options</code></em></span>] [<span class="optional">, ...</span>]); +</pre><p> + The operator class identifies the operators to be used by the index + for that column. For example, a B-tree index on the type <code class="type">int4</code> + would use the <code class="literal">int4_ops</code> class; this operator + class includes comparison functions for values of type <code class="type">int4</code>. + In practice the default operator class for the column's data type is + usually sufficient. The main reason for having operator classes is + that for some data types, there could be more than one meaningful + index behavior. For example, we might want to sort a complex-number data + type either by absolute value or by real part. We could do this by + defining two operator classes for the data type and then selecting + the proper class when making an index. The operator class determines + the basic sort ordering (which can then be modified by adding sort options + <code class="literal">COLLATE</code>, + <code class="literal">ASC</code>/<code class="literal">DESC</code> and/or + <code class="literal">NULLS FIRST</code>/<code class="literal">NULLS LAST</code>). + </p><p> + There are also some built-in operator classes besides the default ones: + + </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> + The operator classes <code class="literal">text_pattern_ops</code>, + <code class="literal">varchar_pattern_ops</code>, and + <code class="literal">bpchar_pattern_ops</code> support B-tree indexes on + the types <code class="type">text</code>, <code class="type">varchar</code>, and + <code class="type">char</code> respectively. The + difference from the default operator classes is that the values + are compared strictly character by character rather than + according to the locale-specific collation rules. This makes + these operator classes suitable for use by queries involving + pattern matching expressions (<code class="literal">LIKE</code> or POSIX + regular expressions) when the database does not use the standard + <span class="quote">“<span class="quote">C</span>”</span> locale. As an example, you might index a + <code class="type">varchar</code> column like this: +</p><pre class="programlisting"> +CREATE INDEX test_index ON test_table (col varchar_pattern_ops); +</pre><p> + Note that you should also create an index with the default operator + class if you want queries involving ordinary <code class="literal"><</code>, + <code class="literal"><=</code>, <code class="literal">></code>, or <code class="literal">>=</code> comparisons + to use an index. Such queries cannot use the + <code class="literal"><em class="replaceable"><code>xxx</code></em>_pattern_ops</code> + operator classes. (Ordinary equality comparisons can use these + operator classes, however.) It is possible to create multiple + indexes on the same column with different operator classes. + If you do use the C locale, you do not need the + <code class="literal"><em class="replaceable"><code>xxx</code></em>_pattern_ops</code> + operator classes, because an index with the default operator class + is usable for pattern-matching queries in the C locale. + </p></li></ul></div><p> + </p><p> + The following query shows all defined operator classes: + +</p><pre class="programlisting"> +SELECT am.amname AS index_method, + opc.opcname AS opclass_name, + opc.opcintype::regtype AS indexed_type, + opc.opcdefault AS is_default + FROM pg_am am, pg_opclass opc + WHERE opc.opcmethod = am.oid + ORDER BY index_method, opclass_name; +</pre><p> + </p><p> + An operator class is actually just a subset of a larger structure called an + <em class="firstterm">operator family</em>. In cases where several data types have + similar behaviors, it is frequently useful to define cross-data-type + operators and allow these to work with indexes. To do this, the operator + classes for each of the types must be grouped into the same operator + family. The cross-type operators are members of the family, but are not + associated with any single class within the family. + </p><p> + This expanded version of the previous query shows the operator family + each operator class belongs to: +</p><pre class="programlisting"> +SELECT am.amname AS index_method, + opc.opcname AS opclass_name, + opf.opfname AS opfamily_name, + opc.opcintype::regtype AS indexed_type, + opc.opcdefault AS is_default + FROM pg_am am, pg_opclass opc, pg_opfamily opf + WHERE opc.opcmethod = am.oid AND + opc.opcfamily = opf.oid + ORDER BY index_method, opclass_name; +</pre><p> + </p><p> + This query shows all defined operator families and all + the operators included in each family: +</p><pre class="programlisting"> +SELECT am.amname AS index_method, + opf.opfname AS opfamily_name, + amop.amopopr::regoperator AS opfamily_operator + FROM pg_am am, pg_opfamily opf, pg_amop amop + WHERE opf.opfmethod = am.oid AND + amop.amopfamily = opf.oid + ORDER BY index_method, opfamily_name, opfamily_operator; +</pre><p> + </p><div class="tip"><h3 class="title">Tip</h3><p> + <a class="xref" href="app-psql.html" title="psql"><span class="refentrytitle"><span class="application">psql</span></span></a> has + commands <code class="command">\dAc</code>, <code class="command">\dAf</code>, + and <code class="command">\dAo</code>, which provide slightly more sophisticated + versions of these queries. + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="indexes-index-only-scans.html" title="11.9. Index-Only Scans and Covering 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-collations.html" title="11.11. Indexes and Collations">Next</a></td></tr><tr><td width="40%" align="left" valign="top">11.9. Index-Only Scans and Covering Indexes </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"> 11.11. Indexes and Collations</td></tr></table></div></body></html>
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