MySQL第五次作业

**一、触发器部分**

1. 订单表中增加订单数量后，商品表商品数量同步减少对应的商品订单出数量

CREATE TRIGGER update_goods_num_after_insert_orders

AFTER INSERT ON orders

FOR EACH ROW

UPDATE goods

SET num = num - NEW.onum

WHERE gid = NEW.gid;

-- 测试

INSERT INTO orders (gid, name, price, onum, otime)

VALUES ('A0001', '橡皮', 2.5, 10, '2024-07-25');

2. 客户取消订单，恢复商品表对应商品的数量

CREATE TRIGGER restore_goods_num_after_cancel_order

AFTER DELETE ON orders

FOR EACH ROW

UPDATE goods

SET num = num + OLD.onum

WHERE gid = OLD.gid;

-- 测试

DELETE FROM orders WHERE oid = 1;

3. 客户修改订单，商品表对应商品数量同步更新

CREATE TRIGGER update_goods_num_after_update_orders

AFTER UPDATE ON orders

FOR EACH ROW

UPDATE goods

SET num = num + OLD.onum - NEW.onum

WHERE gid = NEW.gid;

-- 测试

UPDATE orders SET onum = 20 WHERE oid = 2;

**二、存储过程部分**

1. 创建提取 `emp_new` 表所有员工姓名和工资的存储过程 `s1`

USE mydb7_openlab;

CREATE PROCEDURE s1()

SELECT name, salary FROM emp_new;

2. 创建存储过程 `s2`，实现输入员工姓名后返回员工的年龄

CREATE PROCEDURE s2(IN emp_name VARCHAR(50))

SELECT age FROM emp_new WHERE name = emp_name;

3. 创建一个存储过程 `s3`，有 2 个参数，传入部门号，返回该部门的平均工资

CREATE PROCEDURE s3(IN dept_id INT, OUT avg_salary DECIMAL(10, 2))

SELECT AVG(salary) INTO avg_salary FROM emp_new WHERE department_id = dept_id;