Question

我有一张记录库存数量的表格。我设置触发器以在库存变低时警告用户。测试时，触发器会触发，显示消息，但库存不会更新。我做错了什么？是否有另一种设置触发器的方法（不使用SIGNAL SQLSTATE）？我在uWamp中使用phpMyAdmin 4.2.7.1。谢谢你的建议。

触发器代码：

DELIMITER $$
CREATE TRIGGER low_stock_message  
AFTER update ON stock_quantity 
FOR EACH ROW BEGIN
    IF (NEW.Regular_Menu < 50) THEN 
        SIGNAL SQLSTATE '02000' SET MESSAGE_TEXT = 'Warning, Regular Menu has a low stock!';
    END IF;
    IF (NEW.Savers < 50) THEN 
        SIGNAL SQLSTATE '02000' SET MESSAGE_TEXT = 'Warning, Savers Menu has a low stock';
    END IF;
    IF (NEW.Breakfast < 50) THEN 
        SIGNAL SQLSTATE '02000' SET MESSAGE_TEXT = 'Warning,  Breakfast Menu has a low stock!';
    END IF;
END$$
DELIMITER ;

测试查询：

UPDATE stock_quantity
SET Regular_Menu=48
WHERE Outlet_ID=1;

Answer 1

我怀疑是因为您正在使用SIGNAL SQL STATE '02000'，according to the documentation是一个异常信号。特别是，“如果函数中的信号未处理，则语句结束。”

Answer 2

您必须使用sqlstate '45000'并为此设置message_text。让我用一个例子解释一下..在下面的例子中，我们的目标是阻止用户投票给自己的帖子，如下所示：

<强>存根

create table votes (user_id int);

delimiter //

create trigger prevent_self_votes before insert on votes
for each row
begin
    if (new.user_id = 12) then   // 12 is id of voter
        signal sqlstate '45000' set message_text = 'You cannot vote for yourself, dude!';
    end if;
end //

delimiter ;

PHP脚本

<?php

$db = new PDO('mysql:host=localhost;dbname=test', 'test', 'test');
$sql = 'insert into votes values (:user_id)';
$statement = $db->prepare($sql);
if ($statement === false) {
    echo 'statement is false';
    exit();
}

try {
    $result = $statement->execute(array(':user_id'=>12));
    if ($result === false) {
        $error = $statement->errorInfo();
        print_r($error);
        echo "$error[2] ... is the error reported by trigger\n";
    }
    else {
        print_r($result);
        echo 'Inserted', "\n";
    }
}
catch (PDOException $e) {
    echo $e->getMessage();
}

?>

<强>结果

$ php test.php
Array
(
    [0] => 45000
    [1] => 1644
    [2] => You cannot vote for yourself, dude!
)
You cannot vote for yourself, dude! ... is the error reported by trigger

如您所见，您可以使用$statement->errorInfo()[2]的输出来提取触发器提供的信息。

http://php.net/manual/en/pdo.errorinfo.php表示数组中的第一项是SQLSTATE ANSI SQL错误代码，第二项是驱动程序特定的错误代码，第三项是驱动程序特定的错误消息。

在phpMyAdmin中触发触发器时显示消息

2 个答案: