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<sect1 id="btree-gist">

<title>btree_gist</title>

<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>,

asdescibed below.

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>,

asdescribed below.

</para>

<sect2>

</programlisting>

<para>

Example usingan <link linkend="SQL-CREATETABLE-EXCLUDE">Exclusion

Constraint</link> to enforce theconstraint that a cage at a zoo

Usean <link linkend="SQL-CREATETABLE-EXCLUDE">exclusion

constraint</link> to enforce therule that a cage at a zoo

can contain only one kind of animal:

</para>

<programlisting>

=> CREATE TABLE zoo (

=&gt; CREATE TABLE zoo (

cage INTEGER,

animal TEXT,

EXCLUDE USING gist (cage WITH =, animal WITH<>)

EXCLUDE USING gist (cage WITH =, animal WITH&lt;&gt;)

);

=> INSERT INTO zoo VALUES(123, 'zebra');

=&gt; INSERT INTO zoo VALUES(123, 'zebra');

INSERT 0 1

=> INSERT INTO zoo VALUES(123, 'zebra');

=&gt; INSERT INTO zoo VALUES(123, 'zebra');

INSERT 0 1

=> INSERT INTO zoo VALUES(123, 'lion');

=&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).

=> INSERT INTO zoo VALUES(124, 'lion');

=&gt; INSERT INTO zoo VALUES(124, 'lion');

INSERT 0 1

</programlisting>