DECLARE
  x integer := 1;
  y integer := x + 1;
</programlisting>
     </para>

    <sect2 id="plpgsql-declaration-parameters">
     <title>Declaring Function Parameters</title>

     <para>
      Parameters passed to functions are named with the identifiers
      <literal>$1</literal>, <literal>$2</literal>,
      etc.  Optionally, aliases can be declared for
      <literal>$<replaceable>n</replaceable></literal>
      parameter names for increased readability.  Either the alias or the
      numeric identifier can then be used to refer to the parameter value.
     </para>

     <para>
      There are two ways to create an alias.  The preferred way is to give a
      name to the parameter in the <command>CREATE FUNCTION</command> command,
      for example:
<programlisting>
CREATE FUNCTION sales_tax(subtotal real) RETURNS real AS $$
BEGIN
    RETURN subtotal * 0.06;
END;
$$ LANGUAGE plpgsql;
</programlisting>
      The other way is to explicitly declare an alias, using the
      declaration syntax

<synopsis>
<replaceable>name</replaceable> ALIAS FOR $<replaceable>n</replaceable>;
</synopsis>

      The same example in this style looks like:
<programlisting>
CREATE FUNCTION sales_tax(real) RETURNS real AS $$
DECLARE
    subtotal ALIAS FOR $1;
BEGIN
    RETURN subtotal * 0.06;
END;
$$ LANGUAGE plpgsql;
</programlisting>
     </para>

    <note>
     <para>
      These two examples are not perfectly equivalent.  In the first case,
      <literal>subtotal</literal> could be referenced as
      <literal>sales_tax.subtotal</literal>, but in the second case it could not.
      (Had we attached a label to the inner block, <literal>subtotal</literal> could
      be qualified with that label, instead.)
     </para>
    </note>

     <para>
      Some more examples:
<programlisting>
CREATE FUNCTION instr(varchar, integer) RETURNS integer AS $$
DECLARE
    v_string ALIAS FOR $1;
    index ALIAS FOR $2;
BEGIN
    -- some computations using v_string and index here
END;
$$ LANGUAGE plpgsql;


CREATE FUNCTION concat_selected_fields(in_t sometablename) RETURNS text AS $$
BEGIN
    RETURN in_t.f1 || in_t.f3 || in_t.f5 || in_t.f7;
END;
$$ LANGUAGE plpgsql;
</programlisting>
     </para>

     <para>
      When a <application>PL/pgSQL</application> function is declared
      with output parameters, the output parameters are given
      <literal>$<replaceable>n</replaceable></literal> names and optional
      aliases in just the same way as the normal input parameters.  An
      output parameter is effectively a variable that starts out NULL;
      it should be assigned to during the execution of the function.
      The final value of the parameter is what is returned.  For instance,
      the sales-tax example could also be done this way:

<programlisting>
CREATE FUNCTION sales_tax(subtotal real, OUT tax real) AS $$
BEGIN
    tax := subtotal * 0.06;
END;
$$ LANGUAGE plpgsql;
</programlisting>

      Notice that we omitted <literal>RETURNS real</literal> &mdash; we could have
      included it, but it would be redundant.
     </para>

     <para>
      To call a function with <literal>OUT</literal> parameters, omit the
      output parameter(s) in the function call:
<programlisting>
SELECT sales_tax(100.00);
</programlisting>
     </para>

     <para>
      Output parameters are most useful when returning multiple values.
      A trivial example is:

<programlisting>
CREATE FUNCTION sum_n_product(x int, y int, OUT sum int, OUT prod int) AS $$
BEGIN
    sum := x + y;
    prod := x * y;
END;
$$ LANGUAGE plpgsql;

SELECT * FROM sum_n_product(2, 4);
 sum | prod
-----+------
   6 |    8
</programlisting>

      As discussed in <xref linkend="xfunc-output-parameters"/>, this
      effectively creates an anonymous record type for the function's
      results.  If a <literal>RETURNS</literal> clause is given, it must say
      <literal>RETURNS record</literal>.
     </para>

     <para>
      This also works with procedures, for example:

<programlisting>