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5.4.3 SQL Functions with Parameter Names

It is possible to attach names to a function's parameters, for example

CREATE FUNCTION tf1 (acct_no integer, debit numeric) RETURNS 
  numeric AS $$
    UPDATE bank
        SET balance = balance - $2
        WHERE accountno = $1
    RETURNING balance;
$$ LANGUAGE SQL;

Here the first parameter has been given the name acct_no, and the second parameter the name debit. So far as the SQL function itself is concerned, these names are just decoration; you must still refer to the parameters as $1, $2, etc within the function body. (Some procedural languages let you use the parameter names instead.) However, attaching names to the parameters is useful for documentation purposes. When a function has many parameters, it is also useful to use the names while calling the function, as described in Volume 1A: 2.3 Calling Functions.