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; 'Hello', b =&gt; 'World');
 concat_lower_or_upper
-----------------------
 hello world
(1 row)
</screen>
     Again, the argument <literal>uppercase</literal> was omitted
     so it is set to <literal>false</literal> implicitly.  One advantage of
     using named notation is that the arguments may be specified in any
     order, for example:
<screen>
SELECT concat_lower_or_upper(a =&gt; 'Hello', b =&gt; 'World', uppercase =&gt; true);
 concat_lower_or_upper
-----------------------
 HELLO WORLD
(1 row)

SELECT concat_lower_or_upper(a =&gt; 'Hello', uppercase =&gt; true, b =&gt; 'World');
 concat_lower_or_upper
-----------------------
 HELLO WORLD
(1 row)
</screen>
    </para>

    <para>
      An older syntax based on ":=" is supported for backward compatibility:
<screen>
SELECT concat_lower_or_upper(a := 'Hello', uppercase := true, b := 'World');
 concat_lower_or_upper
-----------------------
 HELLO WORLD
(1 row)
</screen>
    </para>
   </sect2>

  <sect2 id="sql-syntax-calling-funcs-mixed">
   <title>Using Mixed Notation</title>

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

   <para>
    The mixed notation combines positional and named notation. However, as
    already mentioned, named arguments cannot precede positional arguments.
    For example:
<screen>
SELECT concat_lower_or_upper('Hello', 'World', uppercase =&gt; true);
 concat_lower_or_upper
-----------------------
 HELLO WORLD
(1 row)
</screen>
    In the above query, the arguments <literal>a</literal> and
    <literal>b</literal> are specified positionally, while
    <literal>uppercase</literal> is specified by name.  In this example,
    that adds little except documentation.  With a more complex function
    having numerous parameters that have default values, named or mixed
    notation can save a great deal of writing and reduce chances for error.
   </para>

   <note>
    <para>
     Named and mixed call notations currently cannot be used when calling an
     aggregate function (but they do work when an aggregate function is used
     as a window function).
    </para>
   </note>
  </sect2>
 </sect1>

</chapter>