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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.36 2002/08/13 20:40:43 momjian Exp $
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PostgreSQL documentation
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-->
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1999-07-06 19:16:42 +02:00
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<refentry id="SQL-CREATEINDEX">
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<refmeta>
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<refentrytitle id="sql-createindex-title">CREATE INDEX</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>
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CREATE INDEX
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</refname>
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<refpurpose>
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define a new index
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</refpurpose>
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1998-12-29 03:24:47 +01:00
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</refnamediv>
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<refsynopsisdiv>
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<refsynopsisdivinfo>
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<date>2001-07-15</date>
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</refsynopsisdivinfo>
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<synopsis>
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CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable> ON <replaceable class="parameter">table</replaceable>
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[ USING <replaceable class="parameter">acc_method</replaceable> ] ( <replaceable class="parameter">column</replaceable> [ <replaceable class="parameter">ops_name</replaceable> ] [, ...] )
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[ WHERE <replaceable class="parameter">predicate</replaceable> ]
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CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable> ON <replaceable class="parameter">table</replaceable>
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[ USING <replaceable class="parameter">acc_method</replaceable> ] ( <replaceable class="parameter">func_name</replaceable>( <replaceable class="parameter">column</replaceable> [, ... ]) [ <replaceable class="parameter">ops_name</replaceable> ] )
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[ WHERE <replaceable class="parameter">predicate</replaceable> ]
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</synopsis>
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<refsect2 id="R2-SQL-CREATEINDEX-1">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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Inputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term>UNIQUE</term>
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<listitem>
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<para>
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Causes the system to check for
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duplicate values in the table when the index is created (if data
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already exist) and each time data is added. Attempts to
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insert or update data which would result in duplicate entries
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will generate an error.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">index_name</replaceable></term>
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<listitem>
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<para>
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The name of the index to be created. No schema name can be included
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here; the index is always created in the same schema as its parent
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table.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">table</replaceable></term>
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<listitem>
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<para>
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The name (possibly schema-qualified) of the table to be indexed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">acc_method</replaceable></term>
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<listitem>
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<para>
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The name of the access method to be used for the index. The
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default access method is <literal>BTREE</literal>.
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<application>PostgreSQL</application> provides four access
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methods for indexes:
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<variablelist>
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<varlistentry>
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<term><literal>BTREE</></term>
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<listitem>
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<para>
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an implementation of Lehman-Yao
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high-concurrency B-trees.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>RTREE</></term>
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<listitem>
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<para>implements standard R-trees using Guttman's
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quadratic split algorithm.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>HASH</></term>
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<listitem>
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<para>
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an implementation of Litwin's linear hashing.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>GIST</></term>
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<listitem>
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<para>
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Generalized Index Search Trees.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">column</replaceable></term>
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<listitem>
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<para>
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The name of a column of the table.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">ops_name</replaceable></term>
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<listitem>
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<para>
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An associated operator class. See below for details.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">func_name</replaceable></term>
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<listitem>
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<para>
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A function, which returns a value that can be indexed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">predicate</replaceable></term>
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<listitem>
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<para>
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Defines the constraint expression for a partial index.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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1999-07-06 19:16:42 +02:00
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</refsect2>
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<refsect2 id="R2-SQL-CREATEINDEX-2">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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Outputs
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</title>
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<para>
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1998-10-14 18:30:17 +02:00
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1999-07-06 19:16:42 +02:00
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<variablelist>
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<varlistentry>
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<term><computeroutput>
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CREATE INDEX
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</computeroutput></term>
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<listitem>
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<para>
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The message returned if the index is successfully created.
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</para>
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</listitem>
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</varlistentry>
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1998-10-14 18:30:17 +02:00
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1999-07-06 19:16:42 +02:00
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<varlistentry>
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<term><computeroutput>
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ERROR: Cannot create index: 'index_name' already exists.
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</computeroutput></term>
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<listitem>
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<para>
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This error occurs if it is impossible to create the index.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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</refsynopsisdiv>
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<refsect1 id="R1-SQL-CREATEINDEX-1">
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<refsect1info>
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<date>1998-09-09</date>
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</refsect1info>
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<title>
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Description
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</title>
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<para>
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<command>CREATE INDEX</command> constructs an index
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<replaceable class="parameter">index_name</replaceable>
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on the specified <replaceable class="parameter">table</replaceable>.
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1998-12-29 03:24:47 +01:00
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<tip>
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<para>
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Indexes are primarily used to enhance database performance.
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But inappropriate use will result in slower performance.
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</para>
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</tip>
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</para>
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1998-05-13 07:34:00 +02:00
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<para>
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2000-04-23 04:08:33 +02:00
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In the first syntax shown above, the key field(s) for the
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index are specified as column names.
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Multiple fields can be specified if the index access method supports
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multicolumn indexes.
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</para>
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1999-07-06 19:16:42 +02:00
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<para>
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2002-04-12 01:20:04 +02:00
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In the second syntax shown above, an index is defined on the result
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of a user-specified function <replaceable
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class="parameter">func_name</replaceable> applied to one or more
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columns of a single table. These <firstterm>functional
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indexes</firstterm> can be used to obtain fast access to data based
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on operators that would normally require some transformation to apply
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them to the base data. For example, a functional index on
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<literal>upper(col)</> would allow the clause
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<literal>WHERE upper(col) = 'JIM'</> to use an index.
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</para>
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1999-07-22 17:09:15 +02:00
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<para>
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2002-04-12 01:20:04 +02:00
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<application>PostgreSQL</application> provides B-tree, R-tree, hash,
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and GiST access methods for indexes. The B-tree access method is an
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implementation of Lehman-Yao high-concurrency B-trees. The R-tree
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access method implements standard R-trees using Guttman's quadratic
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split algorithm. The hash access method is an implementation of
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Litwin's linear hashing. We mention the algorithms used solely to
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indicate that all of these access methods are fully dynamic and do
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not have to be optimized periodically (as is the case with, for
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example, static hash access methods).
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</para>
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2001-07-16 07:07:00 +02:00
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<para>
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When the <command>WHERE</command> clause is present, a
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<firstterm>partial index</firstterm> is created.
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A partial index is an index that contains entries for only a portion of
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a table, usually a portion that is somehow more interesting than the
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rest of the table. For example, if you have a table that contains both
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billed and unbilled orders where the unbilled orders take up a small
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fraction of the total table and yet that is an often used section, you
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can improve performance by creating an index on just that portion.
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Another possible application is to use <command>WHERE</command> with
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<command>UNIQUE</command> to enforce uniqueness over a subset of a
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table.
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</para>
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<para>
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The expression used in the <command>WHERE</command> clause may refer
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only to columns of the underlying table (but it can use all columns,
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not only the one(s) being indexed). Presently, sub-SELECTs and
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aggregate expressions are also forbidden in <command>WHERE</command>.
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</para>
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<para>
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All functions and operators used in an index definition must be
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<firstterm>immutable</>, that is, their results must depend only on
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their input arguments and never on any outside influence (such as
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the contents of another table or the current time). This restriction
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ensures that the behavior of the index is well-defined. To use a
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user-defined function in an index, remember to mark the function immutable
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when you create it.
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</para>
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2000-05-02 22:02:03 +02:00
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<para>
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2000-12-26 00:15:27 +01:00
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Use <xref linkend="sql-dropindex" endterm="sql-dropindex-title">
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to remove an index.
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</para>
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1999-07-06 19:16:42 +02:00
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<refsect2 id="R2-SQL-CREATEINDEX-3">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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1998-05-13 07:34:00 +02:00
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Notes
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1999-07-06 19:16:42 +02:00
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</title>
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1999-07-22 17:09:15 +02:00
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<para>
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2001-12-08 04:24:40 +01:00
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The <productname>PostgreSQL</productname>
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query optimizer will consider using a B-tree index whenever
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2000-04-23 04:08:33 +02:00
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an indexed attribute is involved in a comparison using one of:
|
1999-07-22 17:09:15 +02:00
|
|
|
|
|
|
|
<simplelist type="inline">
|
|
|
|
<member><</member>
|
|
|
|
<member><=</member>
|
|
|
|
<member>=</member>
|
|
|
|
<member>>=</member>
|
|
|
|
<member>></member>
|
|
|
|
</simplelist>
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
2001-12-08 04:24:40 +01:00
|
|
|
The <productname>PostgreSQL</productname>
|
2002-01-20 23:19:57 +01:00
|
|
|
query optimizer will consider using an R-tree index whenever
|
1999-07-22 17:09:15 +02:00
|
|
|
an indexed attribute is involved in a comparison using one of:
|
|
|
|
|
|
|
|
<simplelist type="inline">
|
|
|
|
<member><<</member>
|
|
|
|
<member>&<</member>
|
|
|
|
<member>&></member>
|
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|
<member>>></member>
|
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|
|
<member>@</member>
|
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<member>~=</member>
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|
<member>&&</member>
|
|
|
|
</simplelist>
|
|
|
|
</para>
|
|
|
|
|
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|
<para>
|
2001-12-08 04:24:40 +01:00
|
|
|
The <productname>PostgreSQL</productname>
|
1999-07-22 17:09:15 +02:00
|
|
|
query optimizer will consider using a hash index whenever
|
|
|
|
an indexed attribute is involved in a comparison using
|
|
|
|
the <literal>=</literal> operator.
|
|
|
|
</para>
|
2002-06-21 05:25:53 +02:00
|
|
|
<para>
|
2002-06-21 21:06:44 +02:00
|
|
|
Testing has shown PostgreSQL's hash indexes to be similar or slower
|
|
|
|
than btree indexes, and the index size and build time for hash
|
|
|
|
indexes is much worse. Hash indexes also suffer poor performance
|
|
|
|
under high concurrency. For these reasons, hash index use is
|
|
|
|
discouraged.
|
2002-06-21 05:25:53 +02:00
|
|
|
</para>
|
1999-07-22 17:09:15 +02:00
|
|
|
|
1999-07-06 19:16:42 +02:00
|
|
|
<para>
|
2002-03-22 20:20:45 +01:00
|
|
|
Currently, only the B-tree and gist access methods support multicolumn
|
2002-08-13 22:40:44 +02:00
|
|
|
indexes. Up to 32 keys may be specified by default (this limit
|
2001-12-08 04:24:40 +01:00
|
|
|
can be altered when building
|
2002-01-20 23:19:57 +01:00
|
|
|
<application>PostgreSQL</application>). Only B-tree currently supports
|
2001-07-16 07:07:00 +02:00
|
|
|
unique indexes.
|
1998-05-13 07:34:00 +02:00
|
|
|
</para>
|
1999-07-22 17:09:15 +02:00
|
|
|
|
2000-04-23 04:08:33 +02:00
|
|
|
<para>
|
|
|
|
An <firstterm>operator class</firstterm> can be specified for each
|
2002-04-12 01:20:04 +02:00
|
|
|
column of an index. The operator class identifies the operators to be
|
|
|
|
used by the index for that column. For example, a B-tree index on
|
2000-04-23 04:08:33 +02:00
|
|
|
four-byte integers would use the <literal>int4_ops</literal> class;
|
|
|
|
this operator class includes comparison functions for four-byte
|
2002-04-12 01:20:04 +02:00
|
|
|
integers. In practice the default operator class for the field's data
|
|
|
|
type is usually sufficient. The main point of having operator classes
|
2000-09-12 22:52:08 +02:00
|
|
|
is that for some data types, there could be more than one meaningful
|
2002-04-12 01:20:04 +02:00
|
|
|
ordering. 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. There are also some operator
|
|
|
|
classes with special purposes:
|
2000-04-23 04:08:33 +02:00
|
|
|
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
The operator classes <literal>box_ops</literal> and
|
2002-01-20 23:19:57 +01:00
|
|
|
<literal>bigbox_ops</literal> both support R-tree indexes on the
|
2000-09-12 22:52:08 +02:00
|
|
|
<literal>box</literal> data type.
|
2000-04-23 04:08:33 +02:00
|
|
|
The difference between them is that <literal>bigbox_ops</literal>
|
2000-10-05 21:48:34 +02:00
|
|
|
scales box coordinates down, to avoid floating-point exceptions from
|
2000-04-23 04:08:33 +02:00
|
|
|
doing multiplication, addition, and subtraction on very large
|
2001-07-16 07:07:00 +02:00
|
|
|
floating-point coordinates. (Note: this was true some time ago,
|
|
|
|
but currently the two operator classes both use floating point
|
|
|
|
and are effectively identical.)
|
2000-04-23 04:08:33 +02:00
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
</itemizedlist>
|
|
|
|
</para>
|
1999-07-22 17:09:15 +02:00
|
|
|
|
|
|
|
<para>
|
2000-04-23 04:08:33 +02:00
|
|
|
The following query shows all defined operator classes:
|
1999-07-22 17:09:15 +02:00
|
|
|
|
|
|
|
<programlisting>
|
2001-07-16 07:07:00 +02:00
|
|
|
SELECT am.amname AS acc_method,
|
2002-07-30 19:34:37 +02:00
|
|
|
opc.opcname AS ops_name
|
|
|
|
FROM pg_am am, pg_opclass opc
|
|
|
|
WHERE opc.opcamid = am.oid
|
|
|
|
ORDER BY acc_method, ops_name;
|
1999-07-22 17:09:15 +02:00
|
|
|
</programlisting>
|
|
|
|
</para>
|
1999-07-06 19:16:42 +02:00
|
|
|
</refsect2>
|
1998-12-29 03:24:47 +01:00
|
|
|
</refsect1>
|
|
|
|
|
1999-07-06 19:16:42 +02:00
|
|
|
<refsect1 id="R1-SQL-CREATEINDEX-2">
|
|
|
|
<title>
|
1998-05-13 07:34:00 +02:00
|
|
|
Usage
|
1999-07-06 19:16:42 +02:00
|
|
|
</title>
|
2002-01-20 23:19:57 +01:00
|
|
|
<para>To create a B-tree index on the field <literal>title</literal>
|
1998-05-13 07:34:00 +02:00
|
|
|
in the table <literal>films</literal>:
|
1999-07-06 19:16:42 +02:00
|
|
|
</para>
|
|
|
|
<programlisting>
|
1998-09-16 16:43:12 +02:00
|
|
|
CREATE UNIQUE INDEX title_idx
|
|
|
|
ON films (title);
|
1999-07-06 19:16:42 +02:00
|
|
|
</programlisting>
|
1998-09-16 16:43:12 +02:00
|
|
|
|
|
|
|
<!--
|
|
|
|
<comment>
|
|
|
|
Is this example correct?
|
|
|
|
</comment>
|
1998-05-13 07:34:00 +02:00
|
|
|
<para>
|
2002-01-20 23:19:57 +01:00
|
|
|
To create a R-tree index on a point attribute so that we
|
1998-05-13 07:34:00 +02:00
|
|
|
can efficiently use box operators on the result of the
|
|
|
|
conversion function:
|
|
|
|
</para>
|
|
|
|
<programlisting>
|
1998-09-16 16:43:12 +02:00
|
|
|
CREATE INDEX pointloc
|
|
|
|
ON points USING RTREE (point2box(location) box_ops);
|
|
|
|
SELECT * FROM points
|
|
|
|
WHERE point2box(points.pointloc) = boxes.box;
|
1998-05-13 07:34:00 +02:00
|
|
|
</programlisting>
|
1998-09-16 16:43:12 +02:00
|
|
|
-->
|
|
|
|
|
1999-07-06 19:16:42 +02:00
|
|
|
</refsect1>
|
1998-05-13 07:34:00 +02:00
|
|
|
|
1999-07-06 19:16:42 +02:00
|
|
|
<refsect1 id="R1-SQL-CREATEINDEX-3">
|
|
|
|
<title>
|
1998-05-13 07:34:00 +02:00
|
|
|
Compatibility
|
1999-07-06 19:16:42 +02:00
|
|
|
</title>
|
1998-05-13 07:34:00 +02:00
|
|
|
|
1999-07-06 19:16:42 +02:00
|
|
|
<refsect2 id="R2-SQL-CREATEINDEX-4">
|
|
|
|
<refsect2info>
|
|
|
|
<date>1998-09-09</date>
|
|
|
|
</refsect2info>
|
|
|
|
<title>
|
1998-05-13 07:34:00 +02:00
|
|
|
SQL92
|
1999-07-06 19:16:42 +02:00
|
|
|
</title>
|
|
|
|
<para>
|
2001-12-08 04:24:40 +01:00
|
|
|
CREATE INDEX is a <productname>PostgreSQL</productname> language extension.
|
1999-07-06 19:16:42 +02:00
|
|
|
</para>
|
1998-05-13 07:34:00 +02:00
|
|
|
<para>
|
1998-09-16 16:43:12 +02:00
|
|
|
There is no <command>CREATE INDEX</command> command in SQL92.
|
1998-05-13 07:34:00 +02:00
|
|
|
</para>
|
|
|
|
</refsect2>
|
|
|
|
</refsect1>
|
1999-07-06 19:16:42 +02:00
|
|
|
</refentry>
|
1998-05-13 07:34:00 +02:00
|
|
|
|
|
|
|
<!-- Keep this comment at the end of the file
|
|
|
|
Local variables:
|
|
|
|
mode: sgml
|
1999-07-06 19:16:42 +02:00
|
|
|
sgml-omittag:nil
|
1998-05-13 07:34:00 +02:00
|
|
|
sgml-shorttag:t
|
|
|
|
sgml-minimize-attributes:nil
|
|
|
|
sgml-always-quote-attributes:t
|
|
|
|
sgml-indent-step:1
|
|
|
|
sgml-indent-data:t
|
|
|
|
sgml-parent-document:nil
|
|
|
|
sgml-default-dtd-file:"../reference.ced"
|
|
|
|
sgml-exposed-tags:nil
|
|
|
|
sgml-local-catalogs:"/usr/lib/sgml/catalog"
|
|
|
|
sgml-local-ecat-files:nil
|
|
|
|
End:
|
|
|
|
-->
|