PostgreSQL Function to calculate IBAN the given a Spanish Acount Number

calculate_iban.sql

CREATE OR REPLACE FUNCTION calculate_iban(account varchar)
RETURNS varchar AS $$
DECLARE num numeric;
DECLARE DC varchar(2);
BEGIN
	SELECT CAST(replace(account, ' ', '')|| '142800' AS numeric) INTO num; 
	SELECT LPAD(CAST(98 - MOD(num, 97) AS varchar(2)), 2, '0') INTO DC;
	RETURN 'ES' || DC || replace(account, ' ', '');
END;
$$ LANGUAGE plpgsql;