求大神给看看哪出问题了

CREATE DEFINER = CURRENT_USER FUNCTION `get_structure_users_count`(`stru_id` int,`islevel` int)

 RETURNS int(11)

BEGIN

	SELECT @lft:=lft FROM dc_structure WHERE id=stru_id;

	SELECT @rgt:=rgt FROM dc_structure WHERE id=stru_id;

	IF(islevel>0)

	THEN

		SELECT @nums := COUNT(*) FROM dc_user u LEFT JOIN dc_structure s ON u.structure_id =s.id WHERE s.lft>=lft and s.rgt <=rgt and u.is_deleted=0;

	ELSE

		SELECT @nums :=  COUNT(*) FROM dc_user u WHERE u.structure_id=stru_id and u.is_deleted=0;

	END IF

	RETURN @nums;

END;