</indexterm>

Ordinary comparison operators yield null (signifying <quote>unknown</>),

not true or false, when either input is null. For example,

<literal>7 = NULL</> yields null. When this behavior is not suitable,

use the

<literal>7 = NULL</> yields null, as does <literal>7 &lt;&gt; NULL</>. When

this behavior is not suitable,use the

<literal>IS <optional> NOT </> DISTINCT FROM</literal> constructs:

<synopsis>

<replaceable>expression</replaceable> IS DISTINCT FROM <replaceable>expression</replaceable>