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<!-- doc/src/sgml/btree-gist.sgml -->
<sect1 id="btree-gist" xreflabel="btree_gist">
<title>btree_gist</title>
<indexterm zone="btree-gist">
<primary>btree_gist</primary>
</indexterm>
<para>
<filename>btree_gist</filename> provides GiST index operator classes that
implement B-tree equivalent behavior for the data types
<type>int2</type>, <type>int4</type>, <type>int8</type>, <type>float4</type>,
<type>float8</type>, <type>numeric</type>, <type>timestamp with time zone</type>,
<type>timestamp without time zone</type>, <type>time with time zone</type>,
<type>time without time zone</type>, <type>date</type>, <type>interval</type>,
<type>oid</type>, <type>money</type>, <type>char</type>,
<type>varchar</type>, <type>text</type>, <type>bytea</type>, <type>bit</type>,
<type>varbit</type>, <type>macaddr</type>, <type>macaddr8</type>, <type>inet</type>,
<type>cidr</type>, <type>uuid</type>, <type>bool</type> and all <type>enum</type> types.
</para>
<para>
In general, these operator classes will not outperform the equivalent
standard B-tree index methods, and they lack one major feature of the
standard B-tree code: the ability to enforce uniqueness. However,
they provide some other features that are not available with a B-tree
index, as described below. Also, these operator classes are useful
when a multicolumn GiST index is needed, wherein some of the columns
are of data types that are only indexable with GiST but other columns
are just simple data types. Lastly, these operator classes are useful for
GiST testing and as a base for developing other GiST operator classes.
</para>
<para>
In addition to the typical B-tree search operators, <filename>btree_gist</filename>
also provides index support for <literal><></literal> (<quote>not
equals</quote>). This may be useful in combination with an
<link linkend="sql-createtable-exclude">exclusion constraint</link>,
as described below.
</para>
<para>
Also, for data types for which there is a natural distance metric,
<filename>btree_gist</filename> defines a distance operator <literal><-></literal>,
and provides GiST index support for nearest-neighbor searches using
this operator. Distance operators are provided for
<type>int2</type>, <type>int4</type>, <type>int8</type>, <type>float4</type>,
<type>float8</type>, <type>timestamp with time zone</type>,
<type>timestamp without time zone</type>,
<type>time without time zone</type>, <type>date</type>, <type>interval</type>,
<type>oid</type>, and <type>money</type>.
</para>
<para>
This module is considered <quote>trusted</quote>, that is, it can be
installed by non-superusers who have <literal>CREATE</literal> privilege
on the current database.
</para>
<sect2>
<title>Example Usage</title>
<para>
Simple example using <literal>btree_gist</literal> instead of <literal>btree</literal>:
</para>
<programlisting>
CREATE TABLE test (a int4);
-- create index
CREATE INDEX testidx ON test USING GIST (a);
-- query
SELECT * FROM test WHERE a < 10;
-- nearest-neighbor search: find the ten entries closest to "42"
SELECT *, a <-> 42 AS dist FROM test ORDER BY a <-> 42 LIMIT 10;
</programlisting>
<para>
Use an <link linkend="sql-createtable-exclude">exclusion
constraint</link> to enforce the rule that a cage at a zoo
can contain only one kind of animal:
</para>
<programlisting>
=> CREATE TABLE zoo (
cage INTEGER,
animal TEXT,
EXCLUDE USING GIST (cage WITH =, animal WITH <>)
);
=> INSERT INTO zoo VALUES(123, 'zebra');
INSERT 0 1
=> INSERT INTO zoo VALUES(123, 'zebra');
INSERT 0 1
=> INSERT INTO zoo VALUES(123, 'lion');
ERROR: conflicting key value violates exclusion constraint "zoo_cage_animal_excl"
DETAIL: Key (cage, animal)=(123, lion) conflicts with existing key (cage, animal)=(123, zebra).
=> INSERT INTO zoo VALUES(124, 'lion');
INSERT 0 1
</programlisting>
</sect2>
<sect2>
<title>Authors</title>
<para>
Teodor Sigaev (<email>teodor@stack.net</email>),
Oleg Bartunov (<email>oleg@sai.msu.su</email>),
Janko Richter (<email>jankorichter@yahoo.de</email>), and
Paul Jungwirth (<email>pj@illuminatedcomputing.com</email>). See
<ulink url="http://www.sai.msu.su/~megera/postgres/gist/"></ulink>
for additional information.
</para>
</sect2>
</sect1>
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