successively
        until the first one that is true is found.  Then the
        associated statement(s) are executed, after which control
        passes to the next statement after <literal>END IF</literal>.
        (Any subsequent <literal>IF</literal> conditions are <emphasis>not</emphasis>
        tested.)  If none of the <literal>IF</literal> conditions is true,
        then the <literal>ELSE</literal> block (if any) is executed.
       </para>

       <para>
        Here is an example:

<programlisting>
IF number = 0 THEN
    result := 'zero';
ELSIF number &gt; 0 THEN
    result := 'positive';
ELSIF number &lt; 0 THEN
    result := 'negative';
ELSE
    -- hmm, the only other possibility is that number is null
    result := 'NULL';
END IF;
</programlisting>
       </para>

       <para>
        The key word <literal>ELSIF</literal> can also be spelled
        <literal>ELSEIF</literal>.
       </para>

       <para>
        An alternative way of accomplishing the same task is to nest
        <literal>IF-THEN-ELSE</literal> statements, as in the
        following example:

<programlisting>
IF demo_row.sex = 'm' THEN
    pretty_sex := 'man';
ELSE
    IF demo_row.sex = 'f' THEN
        pretty_sex := 'woman';
    END IF;
END IF;
</programlisting>
       </para>

       <para>
        However, this method requires writing a matching <literal>END IF</literal>
        for each <literal>IF</literal>, so it is much more cumbersome than
        using <literal>ELSIF</literal> when there are many alternatives.
       </para>
     </sect3>

     <sect3 id="plpgsql-conditionals-simple-case">
      <title>Simple <literal>CASE</literal></title>

<synopsis>
CASE <replaceable>search-expression</replaceable>
    WHEN <replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> <optional> ... </optional></optional> THEN
      <replaceable>statements</replaceable>
  <optional> WHEN <replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> <optional> ... </optional></optional> THEN
      <replaceable>statements</replaceable>
    ... </optional>
  <optional> ELSE
      <replaceable>statements</replaceable> </optional>
END CASE;
</synopsis>

      <para>
       The simple form of <command>CASE</command> provides conditional execution
       based on equality of operands.  The <replaceable>search-expression</replaceable>
       is evaluated (once) and successively compared to each
       <replaceable>expression</replaceable> in the <literal>WHEN</literal> clauses.
       If a match is found, then the corresponding
       <replaceable>statements</replaceable> are executed, and then control
       passes to the next statement after <literal>END CASE</literal>.  (Subsequent
       <literal>WHEN</literal> expressions are not evaluated.)  If no match is
       found, the <literal>ELSE</literal> <replaceable>statements</replaceable> are
       executed; but if <literal>ELSE</literal> is not present, then a
       <literal>CASE_NOT_FOUND</literal> exception is raised.
      </para>

      <para>
       Here is a simple example:

<programlisting>
CASE x
    WHEN 1, 2 THEN
        msg := 'one or two';
    ELSE
        msg := 'other value than one or two';
END CASE;
</programlisting>
      </para>
     </sect3>

     <sect3 id="plpgsql-conditionals-searched-case">
      <title>Searched <literal>CASE</literal></title>

<synopsis>
CASE
    WHEN <replaceable>boolean-expression</replaceable> THEN
      <replaceable>statements</replaceable>
  <optional> WHEN <replaceable>boolean-expression</replaceable> THEN
      <replaceable>statements</replaceable>
    ... </optional>
  <optional> ELSE
      <replaceable>statements</replaceable> </optional>
END CASE;
</synopsis>

      <para>
       The searched form of <command>CASE</command> provides conditional execution
       based on truth of Boolean expressions.  Each <literal>WHEN</literal> clause's
       <replaceable>boolean-expression</replaceable> is evaluated