SQL IMMUTABLE STRICT;
</programlisting>
    Function <function>concat_lower_or_upper</function> has two mandatory
    parameters, <literal>a</literal> and <literal>b</literal>.  Additionally
    there is one optional parameter <literal>uppercase</literal> which defaults
    to <literal>false</literal>.  The <literal>a</literal> and
    <literal>b</literal> inputs will be concatenated, and forced to either
    upper or lower case depending on the <literal>uppercase</literal>
    parameter.  The remaining details of this function
    definition are not important here (see <xref linkend="extend"/> for
    more information).
   </para>

   <sect2 id="sql-syntax-calling-funcs-positional">
    <title>Using Positional Notation</title>

    <indexterm>
     <primary>function</primary>
     <secondary>positional notation</secondary>
    </indexterm>

    <para>
     Positional notation is the traditional mechanism for passing arguments
     to functions in <productname>PostgreSQL</productname>.  An example is:
<screen>
SELECT concat_lower_or_upper('Hello', 'World', true);
 concat_lower_or_upper
-----------------------
 HELLO WORLD
(1 row)
</screen>
     All arguments are specified in order.  The result is upper case since
     <literal>uppercase</literal> is specified as <literal>true</literal>.
     Another example is:
<screen>
SELECT concat_lower_or_upper('Hello', 'World');
 concat_lower_or_upper
-----------------------
 hello world
(1 row)
</screen>
     Here, the <literal>uppercase</literal> parameter is omitted, so it
     receives its default value of <literal>false</literal>, resulting in
     lower case output.  In positional notation, arguments can be omitted
     from right to left so long as they have defaults.
    </para>
   </sect2>

   <sect2 id="sql-syntax-calling-funcs-named">
    <title>Using Named Notation</title>

    <indexterm>
     <primary>function</primary>
     <secondary>named notation</secondary>
    </indexterm>

    <para>
     In named notation, each argument's name is specified using
     <literal>=&gt;</literal> to separate it from the argument expression.
     For example:
<screen>
SELECT concat_lower_or_upper(a =&gt;