SELECT ... WHERE CASE WHEN x <> 0 THEN y/x > 1.5 ELSE false END;

</programlisting>

</para>

<note>

<para>

As described in <xref linkend="xfunc-volatility">, functions and

operators marked <literal>IMMUTABLE</literal> can be evaluated when

the query is planned rather than when it is executed. This means

that constant parts of a subexpression that is not evaluated during

query execution might still be evaluated during query planning.

</para>

</note>

</sect2>

<sect2>