sql test

DROP FUNCTION IF EXISTS getDepartment;
DELIMITER $
CREATE FUNCTION getDepartment(staff_id INT)
RETURNS INT
BEGIN
  DECLARE dep_id INT;
  SET dep_id = NULL;

  SELECT DEPARTMENT.DepId INTO dep_id
  FROM DEPARTMENT
  JOIN STAFF ON(DEPARTMENT.Manager=STAFF.StaffId)
  WHERE DEPARTMENT.Manager = staff_id OR STAFF.Supervisor = staff_id;

  RETURN dep_id;
END $
DELIMITER ;

SELECT StaffId, getDepartment(StaffId) AS DepId
FROM STAFF
ORDER BY DepId, StaffId;