DELIMITER $$
CREATE FUNCTION `A`(x int) RETURNS decimal(12,4)

    DETERMINISTIC
BEGIN

DECLARE result Decimal(12, 4);

set result = (
    SELECT sum(a)
    from X where Id = x
);
RETURN result;
END$$

DELIMITER $$
CREATE FUNCTION `B`(y) RETURNS decimal(12,4)
    DETERMINISTIC
BEGIN

DECLARE result Decimal(12, 4);

set result = (
    SELECT sum(A(X))
    from another_something where Id = y
);


RETURN result;
END$$

DELIMITER $$

CREATE FUNCTION `C`(z) RETURNS decimal(12,4)
    DETERMINISTIC
BEGIN

DECLARE result Decimal(12, 4);

set result = (
    SELECT sum(B(Z))
    from another_table where Id = z
);


RETURN result;
END$$

SELECT VERSION();

5.0.96-log