Arguments of an SQL function can be referenced in the function
     body using either names or numbers.  Examples of both methods appear
     below.
    </para>

    <para>
     To use a name, declare the function argument as having a name, and
     then just write that name in the function body.  If the argument name
     is the same as any column name in the current SQL command within the
     function, the column name will take precedence.  To override this,
     qualify the argument name with the name of the function itself, that is
     <literal><replaceable>function_name</replaceable>.<replaceable>argument_name</replaceable></literal>.
     (If this would conflict with a qualified column name, again the column
     name wins.  You can avoid the ambiguity by choosing a different alias for
     the table within the SQL command.)
    </para>

    <para>
     In the older numeric approach, arguments are referenced using the syntax
     <literal>$<replaceable>n</replaceable></literal>: <literal>$1</literal> refers to the first input
     argument, <literal>$2</literal> to the second, and so on.  This will work
     whether or not the particular argument was declared with a name.
    </para>

    <para>
     If an argument is of a composite type, then the dot notation,
     e.g., <literal><replaceable>argname</replaceable>.<replaceable>fieldname</replaceable></literal> or
     <literal>$1.<replaceable>fieldname</replaceable></literal>, can be used to access attributes of the
     argument.  Again, you might need to qualify the argument's name with the
     function name to make the form with an argument name unambiguous.
    </para>

    <para>
     SQL function arguments can only be used as data values,
     not as identifiers.  Thus for example this is reasonable:
<programlisting>
INSERT INTO mytable VALUES ($1);
</programlisting>
but this will not work:
<programlisting>
INSERT INTO $1 VALUES (42);
</programlisting>
    </para>

    <note>
     <para>
      The ability to use names to reference SQL function arguments was added
      in <productname>PostgreSQL</productname> 9.2.  Functions to be used in
      older servers must use the <literal>$<replaceable>n</replaceable></literal> notation.
     </para>
    </note>
   </sect2>

   <sect2 id="xfunc-sql-base-functions">
    <title><acronym>SQL</acronym> Functions on Base Types</title>

    <para>
     The simplest possible <acronym>SQL</acronym> function has no arguments and
     simply returns a base type, such as <type>integer</type>:

<screen>
CREATE FUNCTION one() RETURNS integer AS $$
    SELECT 1 AS result;
$$ LANGUAGE SQL;

-- Alternative syntax for string literal:
CREATE FUNCTION one() RETURNS integer AS '
    SELECT 1 AS result;
' LANGUAGE SQL;

SELECT one();

 one
-----
   1
</screen>
    </para>

    <para>
     Notice that we defined a column alias within the function body for the result of the function
     (with  the  name <literal>result</literal>),  but this column alias is not visible
     outside the function.  Hence,  the  result  is labeled <literal>one</literal>
     instead of <literal>result</literal>.
    </para>

    <para>
     It is almost as easy to define <acronym>SQL</acronym> functions
     that take base types as arguments:

<screen>
CREATE FUNCTION add_em(x integer, y integer) RETURNS integer AS $$
    SELECT x + y;
$$ LANGUAGE SQL;

SELECT add_em(1, 2) AS answer;

 answer
--------
      3
</screen>
    </para>

    <para>
     Alternatively, we could dispense with names for the arguments and
     use numbers:

<screen>
CREATE FUNCTION add_em(integer, integer) RETURNS integer AS $$
    SELECT $1 + $2;
$$ LANGUAGE SQL;

SELECT add_em(1, 2) AS answer;

 answer
--------
      3
</screen>
    </para>

    <para>
     Here is a more useful function, which might be used to debit a
     bank account:

<programlisting>
CREATE FUNCTION tf1 (accountno integer, debit numeric) RETURNS numeric AS $$
    UPDATE bank
        SET balance = balance - debit