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
我想根据列类型的值加入不同的表。 这是我目前的伪代码:
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
任何人都知道我的意图的真实问题?
答案 0 :(得分:2)
像
这样的东西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
但我强烈建议您重新设计系统以避免多态关系...