Mysql 根据主表中列的值联接表

我想根据列类型的值连接不同的表。 这是我当前的伪代码：

notificationTable
ID              type        typeID      userID
==============================================
1               comment     34          2
2               accept      22          2

eventTable
ID              event       content
===================================
21              post        34  
22              accept      22

commentTable
ID              comment     eventID
===================================
34              'test'      21

有人知道我的真正意图吗？

类似于

SELECT *
FROM notificationTable notification
IF (notification.type == 'comment')
    LEFT JOIN commentTable comment
    ON notification.typeID = comment.ID
ELSEIF (notification.type == 'accept')
    LEFT JOIN evenTable event
    ON notification.typeID = event.ID
WHERE notification.userID = 2

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但我强烈建议重新设计您的系统，以避免多态关系…

这可以通过mysql中的过程实现，也可以通过编码实现。老实说，我建议您甚至不要尝试去弄清楚这一点。听起来你应该专注于改变桌子的布局结构。你想要的结果是什么？

SELECT *
FROM notificationTable notification   
LEFT JOIN commentTable comment
ON (notification.typeID = comment.ID AND notification.type == 'comment')
LEFT JOIN evenTable event
ON (notification.typeID = event.ID AND notification.type == 'accept')
WHERE notification.userID = 2