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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.367 2007/02/2014:04:50 momjian Exp $ -->

<chapter id="functions">

<title>Functions and Operators</title>

expression must be of Boolean type.

</para>

<!-- IS OF does not conform to the ISO SQL behavior, so it is undocumented here

<para>

<indexterm>

<primary>IS OF</primary>

</synopsis>

They return a boolean value based on whether the expression's data

type is one of the listed data types.

</para>

-->

</sect1>

<sect1 id="functions-math">

<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.116 2007/02/2000:25:05 momjian Exp $ -->

<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.117 2007/02/2014:04:50 momjian Exp $ -->

<chapter id="sql-syntax">

<title>SQL Syntax</title>

<row>

<entry><token>IS</token></entry>

<entry></entry>

<entry><literal>IS TRUE</>, <literal>IS FALSE</>, <literal>IS

UNKNOWN</>, <literal>IS NULL</>, <literal>IS OF</></entry>

<entry><literal>IS TRUE</>, <literal>IS FALSE</>, <literal>IS UNKNOWN</>, <literal>IS NULL</></entry>

</row>

<row>