Question

我试图使用MySQL在触发器中编写业务规则，但它不起作用。

我想要做的是，如果条件为false，则插入必须失败并回滚它。问题是MySQL不允许在触发器中使用回滚。

我还试图使用SIGNAL和短信，但它失败了。

代码是：

CREATE TRIGGER tr_NewTeacher
AFTER INSERT ON teachers FOR EACH ROW
BEGIN
    IF (salary > 1300 AND budget < 15000)
    BEGIN
        ROLLBACK TRANSACTION;
    END             
END

Answer 1

在MySQL触发器中，如果失败，将回滚事务。

所以，你必须在触发器体内引发异常：

...
if [Test]
    then

      SIGNAL sqlstate '45001' set message_text = "No way ! You cannot do this !";

    end if ;
...

Answer 2

您应该使用before insert并获取需要使用的列值new

因此触发器将为

delimiter //
create trigger tr_NewTeacher before insert on teacher
for each row 
begin
  if new.salaRY>1300 AND new.budget<15000  then
  signal sqlstate '45000' set message_text = 'Your error message';
 end if;
end;//

delimiter ;

以下是mysql中的测试用例

mysql> create table teacher (id int auto_increment primary key,salaRY int , budget int);
Query OK, 0 rows affected (0.17 sec)

mysql> delimiter //
mysql> create trigger tr_NewTeacher before insert on teacher
    -> for each row 
    -> begin
    ->   if new.salaRY>1300 AND new.budget<15000  then
    ->   signal sqlstate '45000' set message_text = 'Your error message';
    ->  end if;
    -> end;//
Query OK, 0 rows affected (0.14 sec)


mysql> insert into teacher (salaRY,budget) values (1200,16000);
Query OK, 1 row affected (0.04 sec)

mysql> insert into teacher (salaRY,budget) values (1400,13000);
ERROR 1644 (45000): Your error message
mysql> select * from teacher ;
+----+--------+--------+
| id | salaRY | budget |
+----+--------+--------+
|  1 |   1200 |  16000 |
+----+--------+--------+
1 row in set (0.00 sec)

如何在mysql的触发器上编写业务规则

2 个答案: