Mysql怎么在触发器中抛出异常和取消操作

利用一个控制表t_control

例：

mysql> create table t_control(id int primary key);
Query OK, 0 rows affected (0.11 sec)

mysql> insert into t_control values (1);
Query OK, 1 row affected (0.05 sec)

mysql> create table t_bluerosehero(id int primary key,col int);
Query OK, 0 rows affected (0.11 sec)

mysql> delimiter //
mysql> create trigger tr_t_bluerosehero_bi before insert on t_bluerosehero
-> for each row
-> begin
-> if new.col>30 then
-> insert into t_control values (1);
-> end if;
-> end;
-> //
Query OK, 0 rows affected (0.08 sec)

mysql> delimiter ;
mysql>
mysql> insert into t_bluerosehero values (1,20);
Query OK, 1 row affected (0.25 sec)

mysql> insert into t_bluerosehero values (2,40);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'
mysql>
mysql> select * from t_bluerosehero;
+----+------+
| id | col |
+----+------+
| 1 | 20 |
+----+------+
1 row in set (0.00 sec)

mysql>