如何Mysql触发器中抛出一个异常

从Mysql 5.5 开始为我们提供了SIGNAL函数来实现这个功能。

[sql] view plain copy

CREATE TRIGGER `tg_order_create` AFTER INSERT ON `tp_order` FOR EACH ROW BEGIN

DECLARE msg varchar(200)

/*冻结金额*/

IF 2=NEW.condition THEN

UPDATE `tp_user` SET `frozen_amount`=`frozen_amount`+NEW.amount WHERE `id`=NEW.uid AND `amount`-`frozen_amount` >NEW.amount

/*如果余额不足,产生一个错误*/

IF ROW_COUNT() <>1 THEN

set msg = "用户余额不足以完成支付."

SIGNAL SQLSTATE 'HY000' SET MESSAGE_TEXT = msg

END IF

/*扣除金额*/

ELSEIF 3=NEW.condition THEN

UPDATE `tp_user` SET `amount`=`amount`-NEW.amount WHERE `id`=NEW.uid AND `amount`-`frozen_amount` >NEW.amount

/*如果余额不足,产生一个错误*/

IF ROW_COUNT() <>1 THEN

set msg = "用户余额不足以完成支付."

SIGNAL SQLSTATE 'HY000' SET MESSAGE_TEXT = msg

END IF

END IF

END

这里这条触发器的功能是库存 *** 作，当库存足够的时候 减少库存，否则 抛出一个异常并报告商品库存不足:

[sql] view plain copy

CREATE TRIGGER `TG_order_detail_dec_stock` BEFORE INSERT ON `tp_order_detail` FOR EACH ROW BEGIN

DECLARE msg VARCHAR(200)

UPDATE `tp_stock` SET `num`=`num`-NEW.num WHERE `goods_id`=NEW.goods_id AND `mid`=NEW.mid AND `num`>=NEW.num

IF ROW_COUNT() <>1 THEN

SELECT CONCAT(`name`, ' 库存不足.') INTO msg FROM `tp_goods` WHERE `id`=NEW.goods_id

SIGNAL SQLSTATE 'HY000' SET MESSAGE_TEXT = msg

END IF

END

在PHP端的处理(注:使用ThinkPHP框架):

[php] view plain copy

//前面省略若干行....

try {

if (false === ($order_pk = $tbl_order->add($order))) {

$tbl->rollback()

echo json_encode(array('success' =>-1, 'message' =>"创建订单失败!."), JSON_UNESCAPED_UNICODE)

return

}

}catch (\PDOException $e){

$errInfo=$e->errorInfo[2]

$tbl->rollback()

echo json_encode(array('success' =>-1, 'message' =>"创建订单失败!,{$errInfo}"), JSON_UNESCAPED_UNICODE)

return

}

//后面省略若干行....

你一个触发器

当 insert into t20130406 表的时候， 触发。

触发的时候， 干的事情， 是 insert into t20130406 ...

这样不是递归了么？

如果你仅仅是想， 触发的时候， 干的事情，是把 name1 列的数值， 设置为 dd

那是很简单的。

SET new. name1 = 'dd'

就可以了。

下面是一个例子：

mysql>DELIMITER //

mysql>CREATE TRIGGER BeforeInsertTest

-> BEFORE INSERT ON test_trigger_table

->FOR EACH ROW

->BEGIN

-> SET new.val = '100'

->END

->//

Query OK, 0 rows affected (0.02 sec)

mysql>

mysql>INSERT INTO test_trigger_table(id, name) VALUES (1, 'ABC')

->//

Query OK, 1 row affected (0.03 sec)

mysql>select * from test_trigger_table

->//

+------+------+------+

| id | name | val |

+------+------+------+

|1 | ABC | 100 |

+------+------+------+

1 row in set (0.00 sec)

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