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Update obsolete info in CREATE INDEX ref page. (I had fixed the text
description in indices.sgml, but missed the near-duplicate prose in the reference page...)
This commit is contained in:
Tom Lane
parent
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commit
2ee858b5f0
@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.11 2000/04/11 05:39:15 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.12 2000/04/23 02:08:33 tgl Exp $
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Postgres documentation
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-->
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@ -24,9 +24,9 @@ Postgres documentation
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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_name</replaceable> ] ( <replaceable class="parameter">column</replaceable> [ <replaceable class="parameter">ops_name</replaceable>] [, ...] )
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[ USING <replaceable class="parameter">acc_name</replaceable> ] ( <replaceable class="parameter">column</replaceable> [ <replaceable class="parameter">ops_name</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_name</replaceable> ] ( <replaceable class="parameter">func_name</replaceable>( <replaceable class="parameter">col</replaceable> [, ... ]) <replaceable class="parameter">ops_name</replaceable> )
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[ USING <replaceable class="parameter">acc_name</replaceable> ] ( <replaceable class="parameter">func_name</replaceable>( <replaceable class="parameter">column</replaceable> [, ... ]) [ <replaceable class="parameter">ops_name</replaceable> ] )
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</synopsis>
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<refsect2 id="R2-SQL-CREATEINDEX-1">
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@ -74,16 +74,16 @@ CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable>
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<term><replaceable class="parameter">acc_name</replaceable></term>
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<listitem>
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<para>
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the name of the access method which is to be used for
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The name of the access method to be used for
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the index. The default access method is BTREE.
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Postgres provides three access methods for secondary indexes:
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Postgres provides three access methods for indexes:
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<variablelist>
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<varlistentry>
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<term>BTREE</term>
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<listitem>
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<para>
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an implementation of the Lehman-Yao
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an implementation of Lehman-Yao
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high-concurrency btrees.
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</para>
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</listitem>
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@ -133,8 +133,7 @@ CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable>
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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 user-defined function, which returns a value that can
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be indexed.
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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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@ -199,21 +198,15 @@ ERROR: Cannot create index: 'index_name' already exists.
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</para>
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<para>
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In the first syntax shown above, the key fields for the
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index are specified as column names; a column may also have
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an associated operator class. An operator class is used
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to specify the operators to be used for a particular
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index. For example, a btree index on four-byte integers
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would use the <literal>int4_ops</literal> class;
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this operator class includes
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comparison functions for four-byte integers. The default
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operator class is the appropriate operator class for that
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field type.
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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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multi-column indexes.
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</para>
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<para>
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In the second syntax shown above, an index is defined
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on the result of a user-defined function
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on the result of a user-specified function
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<replaceable class="parameter">func_name</replaceable> applied
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to one or more attributes of a single class.
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These <firstterm>functional indices</firstterm>
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@ -224,8 +217,8 @@ ERROR: Cannot create index: 'index_name' already exists.
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<para>
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Postgres provides btree, rtree and hash access methods for
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secondary indices. The btree access method is an implementation of
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the Lehman-Yao high-concurrency btrees. The rtree access method
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indices. The btree access method is an implementation of
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Lehman-Yao high-concurrency btrees. The rtree access method
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implements standard rtrees using Guttman's quadratic split algorithm.
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The hash access method is an implementation of Litwin's linear
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hashing. We mention the algorithms used solely to indicate that all
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@ -243,8 +236,9 @@ ERROR: Cannot create index: 'index_name' already exists.
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</title>
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<para>
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The Postgres query optimizer will consider using btree indices in a scan
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whenever an indexed attribute is involved in a comparison using one of:
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The <productname>Postgres</productname>
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query optimizer will consider using a btree index whenever
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an indexed attribute is involved in a comparison using one of:
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<simplelist type="inline">
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<member><</member>
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@ -255,19 +249,6 @@ ERROR: Cannot create index: 'index_name' already exists.
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</simplelist>
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</para>
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<para>
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Both box classes support indices on the <literal>box</literal> data
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type in <productname>Postgres</productname>.
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The difference between them is that <literal>bigbox_ops</literal>
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scales box coordinates down, to avoid floating point exceptions from
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doing multiplication, addition, and subtraction on very large
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floating-point coordinates. If the field on which your rectangles lie
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is about 20,000 units square or larger, you should use
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<literal>bigbox_ops</literal>.
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The <literal>poly_ops</literal> operator class supports rtree
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indices on <literal>polygon</literal> data.
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</para>
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<para>
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The <productname>Postgres</productname>
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query optimizer will consider using an rtree index whenever
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@ -292,26 +273,56 @@ ERROR: Cannot create index: 'index_name' already exists.
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</para>
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<para>
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Currently, only the BTREE access method supports multi-column
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indexes. Up to 7 keys may be specified.
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Currently, only the btree access method supports multi-column
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indexes. Up to 16 keys may be specified by default (this limit
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can be altered when building Postgres).
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</para>
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<para>
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Use <xref linkend="sql-dropindex-title" endterm="sql-dropindex-title">
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to remove an index.
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</para>
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<para>
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An <firstterm>operator class</firstterm> can be specified for each
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column of an index. The operator class identifies the operators to
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be used by the index for that column. For example, a btree index on
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four-byte integers would use the <literal>int4_ops</literal> class;
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this operator class includes comparison functions for four-byte
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integers. In practice the default operator class for the field's
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datatype is usually sufficient. The main point of having operator classes
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is that for some datatypes, there could be more than one meaningful
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ordering. For example, we might want to sort a complex-number datatype
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either by absolute value or by real part. We could do this by defining
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two operator classes for the datatype and then selecting the proper
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class when making an index. There are also some operator classes with
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special purposes:
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<itemizedlist>
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<listitem>
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<para>
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The operator classes <literal>box_ops</literal> and
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<literal>bigbox_ops</literal> both support rtree indices on the
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<literal>box</literal> datatype.
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The difference between them is that <literal>bigbox_ops</literal>
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scales box coordinates down, to avoid floating point exceptions from
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doing multiplication, addition, and subtraction on very large
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floating-point coordinates. If the field on which your rectangles lie
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is about 20,000 units square or larger, you should use
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<literal>bigbox_ops</literal>.
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</para>
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</listitem>
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<listitem>
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<para>
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The <literal>int24_ops</literal>
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operator class is useful for constructing indices on int2 data, and
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doing comparisons against int4 data in query qualifications.
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Similarly, <literal>int42_ops</literal>
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support indices on int4 data that is to be compared against int2 data
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in queries.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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The <literal>int24_ops</literal>
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operator class is useful for constructing indices on int2 data, and
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doing comparisons against int4 data in query qualifications.
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Similarly, <literal>int42_ops</literal>
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support indices on int4 data that is to be compared against int2 data
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in queries.
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</para>
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<para>
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The following select list returns all ops_names:
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The following query shows all defined operator classes:
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<programlisting>
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SELECT am.amname AS acc_name,
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@ -328,6 +339,11 @@ SELECT am.amname AS acc_name,
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</refsect2>
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</refsect1>
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<para>
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Use <xref linkend="sql-dropindex-title" endterm="sql-dropindex-title">
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to remove an index.
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</para>
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<refsect1 id="R1-SQL-CREATEINDEX-2">
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<title>
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Usage
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