MySQL存储过程中如何使用局部变量？

Mysql> DELIMITER // ;
mysql> Create Procedure Proc_Localvariables()
   -> BEGIN
   -> DECLARE X INT DEFAULT 100;
   -> DECLARE Y INT;
   -> DECLARE Z INT;
   -> DECLARE A INT;
   -> SET Y = 250;
   -> SET Z = 200;
   -> SET A = X+Y+Z;
   -> SELECT X,Y,Z,A;
   -> END //
Query OK, 0 rows affected (0.00 sec)

mysql> Delimiter ; //
mysql> CALL Proc_Localvariables();
+------+------+------+------+
| X    | Y    | Z    | A    |
+------+------+------+------+
| 100  | 250  | 200  | 550  |
+------+------+------+------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.01 sec)