mysql之触发器的使用

cr一：创建goods表和orders表；

mysql> use  mydb16_tirgeer
Database changed
mysql> create table goods(-> gid char(8) primary key,-> name varchar(10),-> price decimal(8,2),->-> num int);
Query OK, 0 rows affected (0.03 sec)```powershell

mysql> create table orders(-> oid int primary key auto_increment,-> gid char(10) not null,-> name varchar(10),-> price decimal(8,2),-> onum int,-> otime date);
Query OK, 0 rows affected (0.01 sec)

二：导入商品记录；```powershell
mysql> insert into goods values('A0001','橡皮',2.5,100),('B0001','小谐本',2.8,210);
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0mysql> insert into goods values('C0001','铅笔',1.2,120),('D0001','计算器',28,20);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0mysql> select * from goods;
+-------+--------+-------+------+
| gid   | name   | price | num  |
+-------+--------+-------+------+
| A0001 | 橡皮   |  2.50 |  100 |
| B0001 | 小谐本 |  2.80 |  210 |
| C0001 | 铅笔   |  1.20 |  120 |
| D0001 | 计算器 | 28.00 |   20 |
+-------+--------+-------+------+
4 rows in set (0.00 sec)

三：

mysql> create trigger orders_after_insert_trigger-> after insert on orders for each row-> update goods set num=num-new.onum-> where gid=new.gid;
Query OK, 0 rows affected (0.01 sec)mysql> insert into orders (gid,name,price,onum,otime) value('C0001','铅笔',1.2,80,now());
Query OK, 1 row affected, 1 warning (0.01 sec)mysql> select * from goods;
+-------+--------+-------+------+
| gid   | name   | price | num  |
+-------+--------+-------+------+
| A0001 | 橡皮   |  2.50 |  100 |
| B0001 | 小谐本 |  2.80 |  210 |
| C0001 | 铅笔   |  1.20 |   40 |
| D0001 | 计算器 | 28.00 |   20 |
+-------+--------+-------+------+
4 rows in set (0.00 sec)mysql> select * from orders;
+-----+-------+------+-------+------+------------+
| oid | gid   | name | price | onum | otime      |
+-----+-------+------+-------+------+------------+
|   1 | C0001 | 铅笔 |  1.20 |   80 | 2024-07-26 |
+-----+-------+------+-------+------+------------+
1 row in set (0.00 sec)

2.

mysql> create trigger orders_after_delete_trigger-> after delete on orders for each row-> update goods set num=num+old.onum-> where gid = old.gid;
Query OK, 0 rows affected (0.00 sec)
mysql> delete From orders where gid='C0001';
Query OK, 1 row affected (0.00 sec)mysql> select * from goods;
+-------+--------+-------+------+
| gid   | name   | price | num  |
+-------+--------+-------+------+
| A0001 | 橡皮   |  2.50 |  100 |
| B0001 | 小谐本 |  2.80 |  210 |
| C0001 | 铅笔   |  1.20 |  120 |
| D0001 | 计算器 | 28.00 |   20 |
+-------+--------+-------+------+
4 rows in set (0.00 sec)mysql> select * from orders;
Empty set (0.00 sec)

3.

mysql> create trigger orders_after_update_trigger-> after update on orders for each row-> update goods set num=num+(old.onum-new.onum)-> where gid=old.gid;
Query OK, 0 rows affected (0.01 sec)mysql> insert into orders (gid,name,price,onum,otime) value('C0001','铅笔',1.2,80,now());
Query OK, 1 row affected, 1 warning (0.00 sec)mysql> select * from orders;
+-----+-------+------+-------+------+------------+
| oid | gid   | name | price | onum | otime      |
+-----+-------+------+-------+------+------------+
|   2 | C0001 | 铅笔 |  1.20 |   80 | 2024-07-26 |
+-----+-------+------+-------+------+------------+
1 row in set (0.00 sec)mysql> select * from goods;
+-------+--------+-------+------+
| gid   | name   | price | num  |
+-------+--------+-------+------+
| A0001 | 橡皮   |  2.50 |  100 |
| B0001 | 小谐本 |  2.80 |  210 |
| C0001 | 铅笔   |  1.20 |   40 |
| D0001 | 计算器 | 28.00 |   20 |
+-------+--------+-------+------+
4 rows in set (0.00 sec)mysql> update orders set onum=35 where gid = 'C0001';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0mysql> select * from orders;
+-----+-------+------+-------+------+------------+
| oid | gid   | name | price | onum | otime      |
+-----+-------+------+-------+------+------------+
|   2 | C0001 | 铅笔 |  1.20 |   35 | 2024-07-26 |
+-----+-------+------+-------+------+------------+
1 row in set (0.00 sec)mysql> select  * from  goods;
+-------+--------+-------+------+
| gid   | name   | price | num  |
+-------+--------+-------+------+
| A0001 | 橡皮   |  2.50 |  100 |
| B0001 | 小谐本 |  2.80 |  210 |
| C0001 | 铅笔   |  1.20 |   85 |
| D0001 | 计算器 | 28.00 |   20 |
+-------+--------+-------+------+
4 rows in set (0.00 sec)

mysql> use mydb7_openlab;
Database changed
mysql> show tables;
+-------------------------+
| Tables_in_mydb7_openlab |
+-------------------------+
| dept                    |
| emp                     |
| emp_new                 |
| user                    |
+-------------------------+
4 rows in set (0.00 sec)delimiter // 
mysql> create  procedure s1()-> begin->          select name,incoming  from emp_new;-> end //
Query OK, 0 rows affected (0.01 sec)mysql> delimiter ;
mysql> call s1();
+------+----------+
| name | incoming |
+------+----------+
| 张三 |     4000 |
| 李四 |     3500 |
| 王五 |     2000 |
| 赵六 |     7500 |
| 荣七 |     8500 |
| 牛八 |     7300 |
+------+----------+
6 rows in set (0.00 sec)Query OK, 0 rows affected (0.02 sec)mysql>

mysql> create procedure s2(in_name varchar(11),out out_age int)-> begin-> select age into out_age from emp_new where name=in_name;-> end //
Query OK, 0 rows affected (0.00 sec)mysql> call s2('王五',@age);-> //
Query OK, 1 row affected (0.00 sec)mysql> delimiter ;
mysql> select @age;
+------+
| @age |
+------+
|   24 |
+------+
1 row in set (0.00 sec)

mysql> create procedure s3(in in_dept int , out avg_sal float)-> begin->          select avg(incoming) into avg_sal from emp_new where dept2=in_dept;-> end //
Query OK, 0 rows affected (0.00 sec)mysql> call s3(101,@avg_sal)//
Query OK, 1 row affected (0.00 sec)mysql> delimiter ;
mysql> select @avg_sal;
+-------------------+
| @avg_sal          |
+-------------------+
| 3166.666748046875 |
+-------------------+
1 row in set (0.00 sec)