Add btree_gist support for searching on "not equals".

Jeff Davis, with slight editorialization by me.

1 files changed, 37 insertions, 1 deletions

diff --git a/doc/src/sgml/btree-gist.sgml b/doc/src/sgml/btree-gist.sgml
index 8264d5a219c..d477f23a2e4 100644
--- a/doc/src/sgml/btree-gist.sgml
+++ b/doc/src/sgml/btree-gist.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/btree-gist.sgml,v 1.5 2010/03/17 17:12:31 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/btree-gist.sgml,v 1.6 2010/08/02 16:26:48 rhaas Exp $ -->
 
 <sect1 id="btree-gist">
  <title>btree_gist</title>
@@ -27,9 +27,21 @@
   GiST operator classes.
  </para>
 
+ <para>
+  In addition to the typical btree search operators, btree_gist also
+  provides search operators for <literal>&lt;&gt;</literal> ("not
+  equals"). This may be useful in combination with an
+  <link linkend="SQL-CREATETABLE-EXCLUDE">Exclusion Constraint</link>,
+  as descibed 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
@@ -38,6 +50,30 @@ CREATE INDEX testidx ON test USING gist (a);
 SELECT * FROM test WHERE a &lt; 10;
 </programlisting>
 
+  <para>
+   Example using an <link linkend="SQL-CREATETABLE-EXCLUDE">Exclusion
+   Constraint</link> to enforce the constraint 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>