来源：http://hi.baidu.com/loveyurui/blog/item/1c657ac9131b9a15bf09e67d.html
+----+------+------+
| Id | sal | num |
+----+------+------+
| 13 | 600 | 10 |
| 14 | 200 | 10 |
| 15 | 300 | 10 |
+----+------+------+
写好的MySQL触发器 如下：
CREATE TRIGGER ins_trig before insert ON hello.yy
FOR EACH ROW
BEGIN
update yy set sal=sal+100 where num>10
END;
这个触发器是可以执行成功的 然后我们测试(激活)
insert into yy values(0,2000,11);
理论上按照触发器的定义插入的值应该为16 2100 11 可是令人郁闷的错误出现了：
ERROR 1442 (HY000): Can't update table 'yy' in stored function/trigger because i
t is already used by statement which invoked this stored function/trigger.
网上找遍了所有的解决办法 最后在国外的一个帖子上找到了solution
将触发器定义改成如下：
CREATE TRIGGER ins_trig before insert ON hello.yy
FOR EACH ROW
BEGIN
if new.num>10 then
set new.sal = new.sal + 100;
end if;
END;
然后插入刚才的测试值就ok了
mysql> insert into yy values(0,2000,11);
Query OK, 1 row affected (0.01 sec)
mysql> select * from yy;
+----+------+------+
| Id | sal | num |
+----+------+------+
| 13 | 600 | 10 |
| 14 | 200 | 10 |
| 15 | 300 | 10 |
| 16 | 2100 | 11 |
+----+------+------+
5 rows in set (0.00 sec)