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1ff01b3902
IDs in SGML are case insensitive, and we have accumulated a mix of upper and lower case IDs, including different variants of the same ID. In XML, these will be case sensitive, so we need to fix up those differences. Going to all lower case seems most straightforward, and the current build process already makes all anchors and lower case anyway during the SGML->XML conversion, so this doesn't create any difference in the output right now. A future XML-only build process would, however, maintain any mixed case ID spellings in the output, so that is another reason to clean this up beforehand. Author: Alexander Lakhin <exclusion@gmail.com>
113 lines
4.1 KiB
Plaintext
113 lines
4.1 KiB
Plaintext
<!-- doc/src/sgml/btree-gist.sgml -->
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<sect1 id="btree-gist" xreflabel="btree_gist">
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<title>btree_gist</title>
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<indexterm zone="btree-gist">
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<primary>btree_gist</primary>
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</indexterm>
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<para>
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<filename>btree_gist</filename> provides GiST index operator classes that
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implement B-tree equivalent behavior for the data types
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<type>int2</type>, <type>int4</type>, <type>int8</type>, <type>float4</type>,
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<type>float8</type>, <type>numeric</type>, <type>timestamp with time zone</type>,
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<type>timestamp without time zone</type>, <type>time with time zone</type>,
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<type>time without time zone</type>, <type>date</type>, <type>interval</type>,
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<type>oid</type>, <type>money</type>, <type>char</type>,
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<type>varchar</type>, <type>text</type>, <type>bytea</type>, <type>bit</type>,
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<type>varbit</type>, <type>macaddr</type>, <type>macaddr8</type>, <type>inet</type>,
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<type>cidr</type>, <type>uuid</type>, and all <type>enum</type> types.
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</para>
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<para>
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In general, these operator classes will not outperform the equivalent
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standard B-tree index methods, and they lack one major feature of the
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standard B-tree code: the ability to enforce uniqueness. However,
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they provide some other features that are not available with a B-tree
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index, as described below. Also, these operator classes are useful
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when a multicolumn GiST index is needed, wherein some of the columns
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are of data types that are only indexable with GiST but other columns
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are just simple data types. Lastly, these operator classes are useful for
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GiST testing and as a base for developing other GiST operator classes.
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</para>
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<para>
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In addition to the typical B-tree search operators, <filename>btree_gist</filename>
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also provides index support for <literal><></literal> (<quote>not
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equals</quote>). This may be useful in combination with an
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<link linkend="sql-createtable-exclude">exclusion constraint</link>,
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as described below.
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</para>
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<para>
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Also, for data types for which there is a natural distance metric,
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<filename>btree_gist</filename> defines a distance operator <literal><-></literal>,
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and provides GiST index support for nearest-neighbor searches using
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this operator. Distance operators are provided for
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<type>int2</type>, <type>int4</type>, <type>int8</type>, <type>float4</type>,
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<type>float8</type>, <type>timestamp with time zone</type>,
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<type>timestamp without time zone</type>,
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<type>time without time zone</type>, <type>date</type>, <type>interval</type>,
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<type>oid</type>, and <type>money</type>.
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</para>
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<sect2>
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<title>Example Usage</title>
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<para>
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Simple example using <literal>btree_gist</literal> instead of <literal>btree</literal>:
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</para>
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<programlisting>
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CREATE TABLE test (a int4);
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-- create index
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CREATE INDEX testidx ON test USING GIST (a);
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-- query
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SELECT * FROM test WHERE a < 10;
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-- nearest-neighbor search: find the ten entries closest to "42"
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SELECT *, a <-> 42 AS dist FROM test ORDER BY a <-> 42 LIMIT 10;
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</programlisting>
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<para>
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Use an <link linkend="sql-createtable-exclude">exclusion
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constraint</link> to enforce the rule that a cage at a zoo
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can contain only one kind of animal:
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</para>
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<programlisting>
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=> CREATE TABLE zoo (
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cage INTEGER,
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animal TEXT,
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EXCLUDE USING GIST (cage WITH =, animal WITH <>)
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);
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=> INSERT INTO zoo VALUES(123, 'zebra');
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INSERT 0 1
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=> INSERT INTO zoo VALUES(123, 'zebra');
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INSERT 0 1
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=> INSERT INTO zoo VALUES(123, 'lion');
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ERROR: conflicting key value violates exclusion constraint "zoo_cage_animal_excl"
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DETAIL: Key (cage, animal)=(123, lion) conflicts with existing key (cage, animal)=(123, zebra).
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=> INSERT INTO zoo VALUES(124, 'lion');
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INSERT 0 1
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</programlisting>
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</sect2>
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<sect2>
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<title>Authors</title>
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<para>
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Teodor Sigaev (<email>teodor@stack.net</email>),
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Oleg Bartunov (<email>oleg@sai.msu.su</email>),
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Janko Richter (<email>jankorichter@yahoo.de</email>), and
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Paul Jungwirth (<email>pj@illuminatedcomputing.com</email>). See
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<ulink url="http://www.sai.msu.su/~megera/postgres/gist/"></ulink>
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for additional information.
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</para>
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</sect2>
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</sect1>
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