Convert currencies

convert_currencies.sql

CREATE FUNCTION `convert_currency`(cur_from INT, cur_to INT, amount DOUBLE, rate_rub DOUBLE, rate_dollar DOUBLE, rate_euro DOUBLE) 
   RETURNS double DETERMINISTIC
BEGIN
	DECLARE result DOUBLE DEFAULT amount;
	DECLARE delta DOUBLE;

	DECLARE TYPE_DOLLAR INT;
	DECLARE TYPE_EURO INT;
	DECLARE TYPE_RUBLES INT;

	SET TYPE_DOLLAR = 0;
	SET TYPE_EURO = 1;
	SET TYPE_RUBLES = 2;

	IF cur_from = TYPE_DOLLAR THEN -- FROM DOLLAR
		IF cur_to = TYPE_EURO THEN -- TO EURO
			SET delta = rate_dollar / rate_euro;
			SET result = delta * amount;
		ELSEIF cur_to = TYPE_RUBLES THEN -- TO RUBLES
			SET result = amount * rate_dollar;
		END IF;
	ELSEIF cur_from = TYPE_EURO THEN -- FROM EURO
		IF cur_to = TYPE_DOLLAR THEN -- TO DOLLAR
			SET delta = rate_euro / rate_dollar;
			SET result = delta * amount;
		ELSEIF cur_to = TYPE_RUBLES THEN -- TO RUBLES
			SET result = amount * rate_euro;
		END IF;
	ELSE -- FROM RUBLES
		IF cur_to = TYPE_DOLLAR THEN -- TO DOLLAR
			SET result = amount / rate_dollar;
		ELSEIF cur_to = TYPE_EURO THEN -- TO EURO
			SET result = amount / rate_euro;
		END IF;
	END IF;

	RETURN result;

END;