MySQL游标和控制结构代码学习

-- Procedure to find the orderid with the largest amount
-- could be done with max,but just to illustrate stored procedure principles
-- Database movies(20140420)

DELIMITER //
CREATE PROCEDURE largest_order(OUT largest_id INT)
BEGIN
DECLARE this_id INT;
DECLARE this_amount FLOAT;
DECLARE 1_amount FLOAT DEFAULT 0.0;
DECLARE 1_id INT;

DECLARE done INT DEFAULT 0;
DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1;
DECLARE c1 CURSOR FOR SELECT tag_id,kind_id FROM tmp_tags;

OPEN c1;
REPEAT
FETCH c1 INTO this_id,this_amount;
IF NOT done THEN
IF this_amount > 1_amount THEN
SET 1_amount = this_amount;
SET 1_id = this_id;
END IF;
END IF;
UNTIL DONE END REPEAT;
CLOSE c1;

SET largest_id = 1_id;

END
//

DELIMITER ;

在MySQL控制台运行上述代码，出现报错信息：

ERROR 1338 (42000): Cursor declaration after handler declaration

尝试下面的方法

cursor的声明放在handler前面

SQL代码变为

-- Procedure to find the orderid with the largest amount
-- could be done with max,but just to illustrate stored procedure principles
-- Database movies(20140420)

DELIMITER //
CREATE PROCEDURE largest_order(OUT largest_id INT)
BEGIN
DECLARE this_id INT;
DECLARE this_amount FLOAT;
DECLARE 1_amount FLOAT DEFAULT 0.0;
DECLARE 1_id INT;

DECLARE done INT DEFAULT 0;
DECLARE c1 CURSOR FOR SELECT tag_id,kind_id FROM tmp_tags;
DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1;

OPEN c1;
REPEAT
FETCH c1 INTO this_id,this_amount;
IF NOT done THEN
IF this_amount > 1_amount THEN
SET 1_amount = this_amount;
SET 1_id = this_id;
END IF;
END IF;
UNTIL DONE END REPEAT;
CLOSE c1;

SET largest_id = 1_id;

END
//

DELIMITER ;

改成上面的代码之后，可以运行。

执行上述SQL语句之后，在执行下面的语句

CALL largest_order(@l);
SELECT @l;
执行结果是