the return value if desired,
      though that is not required.  <literal>$0</literal> can also be
      given an alias.  For example, this function works on any data type
      that has a <literal>+</literal> operator:

<programlisting>
CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement)
RETURNS anyelement AS $$
DECLARE
    result ALIAS FOR $0;
BEGIN
    result := v1 + v2 + v3;
    RETURN result;
END;
$$ LANGUAGE plpgsql;
</programlisting>
     </para>

     <para>
      The same effect can be obtained by declaring one or more output parameters as
      polymorphic types.  In this case the
      special <literal>$0</literal> parameter is not used; the output
      parameters themselves serve the same purpose.  For example:

<programlisting>
CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement,
                                 OUT sum anyelement)
AS $$
BEGIN
    sum := v1 + v2 + v3;
END;
$$ LANGUAGE plpgsql;
</programlisting>
     </para>

     <para>
      In practice it might be more useful to declare a polymorphic function
      using the <type>anycompatible</type> family of types, so that automatic
      promotion of the input arguments to a common type will occur.
      For example:

<programlisting>
CREATE FUNCTION add_three_values(v1 anycompatible, v2 anycompatible, v3 anycompatible)
RETURNS anycompatible AS $$
BEGIN
    RETURN v1 + v2 + v3;
END;
$$ LANGUAGE plpgsql;
</programlisting>

      With this example, a call such as

<programlisting>
SELECT add_three_values(1, 2, 4.7);
</programlisting>

      will work, automatically promoting the integer inputs to numeric.
      The function using <type>anyelement</type> would require you to
      cast the three inputs to the same type manually.
     </para>
    </sect2>

  <sect2 id="plpgsql-declaration-alias">
   <title><literal>ALIAS</literal></title>

<synopsis>
<replaceable>newname</replaceable> ALIAS FOR <replaceable>oldname</replaceable>;
</synopsis>

   <para>
    The <literal>ALIAS</literal> syntax is more general than is suggested in the
    previous section: you can declare an alias for any variable, not just
    function parameters.  The main practical use for this is to assign
    a different name for variables with predetermined names, such as
    <varname>NEW</varname> or <varname>OLD</varname> within
    a trigger function.
   </para>

   <para>
    Examples:
<programlisting>
DECLARE
  prior ALIAS FOR old;
  updated ALIAS FOR new;
</programlisting>
   </para>

   <para>
    Since <literal>ALIAS</literal> creates two different ways to name the same
    object, unrestricted use can be confusing.  It's best to use it only
    for the purpose of overriding predetermined names.
   </para>
   </sect2>

  <sect2 id="plpgsql-declaration-type">
   <title>Copying Types</title>

<synopsis>
<replaceable>name</replaceable> <replaceable>table</replaceable>.<replaceable>column</replaceable>%TYPE
<replaceable>name</replaceable> <replaceable>variable</replaceable>%TYPE
</synopsis>

   <para>
    <literal>%TYPE</literal> provides the data type of a table column
    or a previously-declared <application>PL/pgSQL</application>
    variable. You can use this to declare variables that will hold
    database values. For example, let's say you have a column named
    <literal>user_id</literal> in your <literal>users</literal>
    table. To declare a variable with the same data type as
    <literal>users.user_id</literal> you write:
<programlisting>
user_id users.user_id%TYPE;
</programlisting>
   </para>

   <para>
    It is also possible to write array decoration
    after <literal>%TYPE</literal>, thereby creating a variable that holds
    an array of the referenced type:
<programlisting>
user_ids users.user_id%TYPE[];
user_ids users.user_id%TYPE ARRAY[4];  -- equivalent to the above
</programlisting>
    Just as when declaring table columns that are arrays, it doesn't
    matter whether you write multiple bracket pairs or specific