MySQL の再帰ストアド プロシージャはどのように数量階層を計算できますか?

DELIMITER $$

CREATE PROCEDURE calctotal(
   IN number INT,
   OUT total INT
)

BEGIN

   DECLARE parent_ID INT DEFAULT NULL ;
   DECLARE tmptotal INT DEFAULT 0;
   DECLARE tmptotal2 INT DEFAULT 0;

   SELECT parentid   FROM test   WHERE id = number INTO parent_ID;   
   SELECT quantity   FROM test   WHERE id = number INTO tmptotal;     

   IF parent_ID IS NULL
    THEN
    SET total = tmptotal;
   ELSE     
    CALL calctotal(parent_ID, tmptotal2);
    SET total = tmptotal2 * tmptotal;   
   END IF;

END$$

DELIMITER ;

SET @@GLOBAL.max_sp_recursion_depth = 255;
SET @@session.max_sp_recursion_depth = 255;

CALL calctotal(6, @total);
SELECT @total;