<!-- doc/src/sgml/btree-gist.sgml -->

<sect1 id="btree-gist">
 <title>btree_gist</title>

 <indexterm zone="btree-gist">
  <primary>btree_gist</primary>
 </indexterm>

 <para>
  <filename>btree_gist</> provides sample GiST operator classes that
  implement B-tree equivalent behavior for the data types
  <type>int2</>, <type>int4</>, <type>int8</>, <type>float4</>,
  <type>float8</>, <type>numeric</>, <type>timestamp with time zone</>,
  <type>timestamp without time zone</>, <type>time with time zone</>,
  <type>time without time zone</>, <type>date</>, <type>interval</>,
  <type>oid</>, <type>money</>, <type>char</>,
  <type>varchar</>, <type>text</>, <type>bytea</>, <type>bit</>,
  <type>varbit</>, <type>macaddr</>, <type>inet</>, and <type>cidr</>.
 </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 are useful for GiST testing and as a base for developing other
  GiST operator classes.
 </para>

 <para>
  In addition to the typical btree search operators, btree_gist also
  provides search operators for <literal>&lt;&gt;</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>

 <sect2>
  <title>Example usage</title>

  <para>
   Simple example using btree_gist instead of btree:
  </para>

<programlisting>
CREATE TABLE test (a int4);
-- create index
CREATE INDEX testidx ON test USING gist (a);
-- query
SELECT * FROM test WHERE a &lt; 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>
=&gt; CREATE TABLE zoo (
  cage   INTEGER,
  animal TEXT,
  EXCLUDE USING gist (cage WITH =, animal WITH &lt;&gt;)
);

=&gt; INSERT INTO zoo VALUES(123, 'zebra');
INSERT 0 1
=&gt; INSERT INTO zoo VALUES(123, 'zebra');
INSERT 0 1
=&gt; 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).
=&gt; 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>), and
   Janko Richter (<email>jankorichter@yahoo.de</email>).  See
   <ulink url="http://www.sai.msu.su/~megera/postgres/gist/"></ulink>
   for additional information.
  </para>

 </sect2>

</sect1>
