Question

我开始收到错误：

错误代码：1109。字段列表中的未知表'LeaderBoard'

我实施了以下触发器后：

USE `broadside`;
DELIMITER $$
CREATE DEFINER=`root`@`localhost` TRIGGER `LeaderBoard_AINS` 
AFTER INSERT ON `LeaderBoard` 
FOR EACH ROW
BEGIN
    if ((broadside.LeaderBoard.username= NEW.username) AND (broadside.LeaderBoard.userscore< NEW.userscore))
    then
        DELETE FROM `broadside`.`LeaderBoard`
        WHERE (username = NEW.username AND userscore != NEW.userscore);
    end if;
    if (broadside.LeaderBoard.username= NEW.username AND broadside.LeaderBoard.userscore< NEW.userscore)
    then
        DELETE FROM `broadside`.`LeaderBoard`
        WHERE (username = NEW.username AND userscore != NEW.userscore);
    end if;
end

表名是LeaderBoard，数据库名称是broadside。它编译得很好，但是当我尝试插入一个元素并且触发器实际上被触发时，我得到上面显示的1109错误。有人可以帮忙吗？

Answer 1

在if条件中，删除引用表并直接比较值。

更改

IF (
    ( broadside.LeaderBoard.username = NEW.username )
    AND
    ( broadside.LeaderBoard.userscore < NEW.userscore )
) THEN

致：

IF (
    ( username = NEW.username ) AND ( userscore < NEW.userscore )
) THEN

顺便说一句：为什么你需要第二个if条件？

参考：MySQL论坛上的类似帖子 MySQL Forums :: Triggers :: #1109 - Unknown table 'xyz' in field list

Answer 2

您必须执行以下操作：

...
IF EXISTS(SELECT NULL FROM `leaderboard` WHERE `username` = NEW.`username` AND `userscore` < NEW.`userscore`) THEN
...

但是，您会遇到如下错误：

Error Code : 1442
Can't update table 'leaderboard' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.

尝试执行DELETE时，原因是：

B.5. MySQL 5.6 FAQ: Triggers：B.5.9: Can triggers access tables?

触发器可以访问自己的表中的旧数据和新数据。一个触发器   也可以影响其他表，但不允许修改   已经被使用（用于读或写）的表   调用函数或触发器的语句。

＆＃34;错误代码：1109。未知表＆＃39; LeaderBoard＆＃39;在字段列表＆＃34;在MYSQL中

2 个答案: