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....

springboot如何判断mysql故障：1、抛出的异常为非运行时异常：2、try -catch 将异常捕捉：3、需要执行事务的方法发生了代理，代理没有向上抛出异常：4、多线程状态下，运行同一段需要执行事务的代码。

直接使用try...catch....结构。比如：

try

{

DB::query("SELECT count(*) FROM pre_111 WHERE fid = $fid"

}

catch（exception $ex）

{

echo($ex->getMessage())

}

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