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<chapter id="functions">

<title>Functions and Operators</title>

<literal>IS NOT NULL</literal>, respectively, except that the input

expression must be of Boolean type.

</para>

<para>

<indexterm>

<primary>IS OF</primary>

</indexterm>

<indexterm>

<primary>IS NOT OF</primary>

</indexterm>

It is possible to check the data type of an expression using the

constructs

<synopsis>

<replaceable>expression</replaceable> IS OF (typename, ...)

<replaceable>expression</replaceable> IS NOT OF (typename, ...)

</synopsis>

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

type is one of the listed data types.

</sect1>

<sect1 id="functions-math">

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<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</></entry>

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

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

</row>

<row>