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<REFENTRY ID="SQL-CREATEINDEX">
<REFMETA>
<REFENTRYTITLE>
CREATE INDEX
</REFENTRYTITLE>
<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
</REFMETA>
<REFNAMEDIV>
<REFNAME>
CREATE INDEX
</REFNAME>
<REFPURPOSE>
Constructs a secondary index
</REFPURPOSE>
<REFSYNOPSISDIV>
<REFSYNOPSISDIVINFO>
</REFSYNOPSISDIVINFO>
<SYNOPSIS>
CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable>
ON <replaceable class="parameter">table</replaceable> [ USING <replaceable class="parameter">acc_name</replaceable> ]
( <replaceable class="parameter">column</replaceable> [ <replaceable class="parameter">ops_name</replaceable>] [, ...] )
CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable>
ON <replaceable class="parameter">table</replaceable> [ USING <replaceable class="parameter">acc_name</replaceable> ]
( <replaceable class="parameter">func_name</replaceable>( <replaceable class="parameter">column</replaceable> [, ... ]) <replaceable class="parameter">ops_name</replaceable> )
</SYNOPSIS>
<REFSECT2 ID="R2-SQL-CREATEINDEX-1">
<REFSECT2INFO>
</REFSECT2INFO>
<TITLE>
Inputs
</TITLE>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
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duplicate values when the index is created (if data
already exist) and each time data is added. Attempts to
insert or update non-duplicate data will generate an
error.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">index_name</replaceable>
</TERM>
<LISTITEM>
<PARA>
The name of the index to be created.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">table</replaceable>
</TERM>
<LISTITEM>
<PARA>
The name of the table to be indexed.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">acc_name</replaceable>
</TERM>
<LISTITEM>
<PARA>
the name of the access method which is to be used for
the index. The default access method is BTREE.
Postgres provides three access methods for secondary indices:
<variablelist>
<varlistentry>
<term>BTREE</term>
<listitem>
<para>
an implementation of the Lehman-Yao
high-concurrency btrees.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>RTREE</term>
<listitem>
<para>implements standard rtrees using Guttman's
quadratic split algorithm.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>HASH</term>
<listitem>
<para>
an implementation of Litwin's linear hashing.
</para>
</listitem>
</varlistentry>
</variablelist>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">column</replaceable>
</TERM>
<LISTITEM>
<PARA>
The name of a column of the table.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">ops_name</replaceable>
</TERM>
<LISTITEM>
<PARA>
An associated operator class.
The following select list returns all ops_names:
<programlisting>
SELECT am.amname AS acc_name,
opc.opcname AS ops_name,
opr.oprname AS ops_comp
FROM pg_am am, pg_amop amop,
pg_opclass opc, pg_operator opr
WHERE amop.amopid = am.oid AND
amop.amopclaid = opc.oid AND
amop.amopopr = opr.oid
ORDER BY acc_name, ops_name, ops_comp
</programlisting>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">func_name</replaceable>
</TERM>
<LISTITEM>
<PARA>
A user-defined function, which returns a value that can
be indexed.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</REFSECT2>
<REFSECT2 ID="R2-SQL-CREATEINDEX-2">
<REFSECT2INFO>
</REFSECT2INFO>
<TITLE>
Outputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<replaceable>status</replaceable>
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</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<ReturnValue>CREATE</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The message returned if the index is successfully created.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue>ERROR: Cannot create index: 'index_name' already exists.</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
This error occurs if it is impossible to create the index.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</REFSECT2>
</REFSYNOPSISDIV>
<REFSECT1 ID="R1-SQL-CREATEINDEX-1">
<REFSECT1INFO>
</REFSECT1INFO>
<TITLE>
Description
</TITLE>
<PARA>
This command constructs an index
<replaceable class="parameter">index_name</replaceable>.
on the specified
<replaceable class="parameter">table</replaceable>.
<tip>
<para>
Indices are primarily used to enhance database performance.
But inappropriate use will result in slower performance.
</tip>
<para>
In the first syntax shown above, the key fields for the
index are specified as column names; a column may also have
an associated operator class. An operator class is used
to specify the operators to be used for a particular
index. For example, a btree index on four-byte integers
would use the <literal>int4_ops</literal> class;
this operator class includes
comparison functions for four-byte integers. The default
operator class is the appropriate operator class for that
field type.
</para>
<para>
In the second syntax, an index is defined
on the result of a user-defined function
<replaceable class="parameter">func_name</replaceable> applied
to one or more attributes of a single class. These functional
indices can be used to obtain fast access to data
based on operators that would normally require some
transformation to apply them to the base data.
</para>
<REFSECT2 ID="R2-SQL-CREATEINDEX-3">
<REFSECT2INFO>
</REFSECT2INFO>
<TITLE>
Notes
</TITLE>
<PARA>
Currently, only the BTREE access method supports multi-column
indices. Up to 7 keys may be specified.
</PARA>
<para>
Use <command>DROP INDEX</command>
to remove an index.
</para>
</REFSECT2>
<REFSECT1 ID="R1-SQL-CREATEINDEX-2">
<TITLE>
Usage
</TITLE>
<PARA>To create a btree index on the field <literal>title</literal>
in the table <literal>films</literal>:
</PARA>
<ProgramListing>
CREATE UNIQUE INDEX title_idx
ON films (title);
<!--
<comment>
Is this example correct?
</comment>
<para>
To create a rtree index on a point attribute so that we
can efficiently use box operators on the result of the
conversion function:
</para>
<programlisting>
CREATE INDEX pointloc
ON points USING RTREE (point2box(location) box_ops);
SELECT * FROM points
WHERE point2box(points.pointloc) = boxes.box;
</REFSECT1>
<REFSECT1 ID="R1-SQL-CREATEINDEX-3">
<TITLE>
Compatibility
</TITLE>
<PARA>
</PARA>
<REFSECT2 ID="R2-SQL-CREATEINDEX-4">
<REFSECT2INFO>
</REFSECT2INFO>
<TITLE>
SQL92
</TITLE>
<PARA>
CREATE INDEX is a <productname>Postgres</productname> language extension.
There is no <command>CREATE INDEX</command> command in SQL92.
</para>
</refsect2>
</refsect1>
</REFENTRY>
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