mysql - 在 MySql 中更新表时验证行项目金额的触发器

Question

我正在为学校开发一个实验室，其中规定:“创建一个名为 products_before_update 的触发器，用于检查 Products 表的discount_percent 列的新值。如果折扣百分比大于 100 或小于0。

如果新折扣百分比介于 0 和 1 之间，则此触发器应将新折扣百分比乘以 100 来修改。这样，折扣百分比 0.2 就会变为 20。

使用适当的 UPDATE 语句测试此触发器。”

我的脚本成功更新了折扣百分比列，但是“如果，那么”部分似乎没有完成任何任务。如果我输入超过 100 的折扣百分比，它不会显示任何错误，只会更新它。如果我的折扣百分比小于零，同样的问题。另外，如果我输入 0-1 之间的数字，那么它不会乘以 10。任何建议将不胜感激!

这是我的代码:

USE my_guitar_shop;

DROP TRIGGER IF EXISTS products_before_update;

DELIMITER //

CREATE TRIGGER products_before_update
   BEFORE UPDATE ON Products
   FOR EACH ROW
BEGIN
DECLARE discount_percent_amount INT;

SELECT discount_percent
INTO discount_percent_amount
FROM Products
WHERE product_id = NEW.product_id;

IF discount_percent_amount > 100 THEN
SIGNAL SQLSTATE 'HY000'
    set message_text = 
        'the discount percent cannot be greater than 100';
ELSEIF discount_percent_amount < 0 THEN
SIGNAL SQLSTATE 'HY000'
    set message_text = 
        'the discount percent cannot be less than 0';
ELSEIF discount_percent_amount < 1 THEN
SET discount_percent_amount = (discount_percent * 10);
END IF;

END//

DELIMITER ;

UPDATE Products
SET discount_percent = .4
WHERE product_id = 3;

SELECT * FROM products;

Answer 1

我终于明白了，谢谢你的提示......

USE my_guitar_shop;

DROP TRIGGER IF EXISTS products_before_update;

DELIMITER //

CREATE TRIGGER products_before_update
  BEFORE UPDATE ON Products
  FOR EACH ROW
BEGIN
IF NEW.discount_percent > 100 THEN
SIGNAL SQLSTATE 'HY000'
    set message_text = 
        'the discount percent cannot be greater than 100';
ELSEIF new.discount_percent < 0 THEN
SIGNAL SQLSTATE 'HY000'
    set message_text = 
        'the discount percent cannot be less than 0';
ELSEIF NEW.discount_percent < 1 THEN
SET NEW.discount_percent = (NEW.discount_percent * 100);
END IF;

END//

DELIMITER ;

UPDATE Products
SET discount_percent = .4
WHERE product_id = 3;