mysql根據列的值連接多個表

Question

我正在使用帖子表和兩種類型的實體學校和用戶可以向該表添加內容。 post 表有一個 post_from 字段來區分帖子是來自用戶還是來自學校。

我想根據 post_from 字段編寫一個連接到用戶表或學校表的查詢。

SELECT *
FROM post    
LEFT JOIN `user`
ON (user.id = post.uid AND post.post_type = 'user' )
LEFT JOIN school_profile
ON (school_profile.id = post.school_id AND post.post_type  = 'school')

Answer 1

你可以用 union 來做到這一點：

SELECT post.*
FROM post    
INNER RJOIN `user`
ON (user.id = post.uid AND post.post_type = 'user' )

union

SELECT post.*
FROM post    
INNER JOIN school_profile
ON (school_profile.id = post.school_id AND post.post_type  = 'school')

或者，您可以這樣做：

SELECT *
FROM post    
LEFT JOIN `user` ON (user.id = post.uid)
LEFT JOIN school_profile ON (school_profile.id = post.school_id)
WHERE post.post_type IN ('user', 'shcool')