獲取未記錄在聯接表中的行

Question

我得到了上面顯示的這3張桌子。

我的目標是獲取user 1（jm）沒有反應的所有bits 。

目前，我有以下MySQL代碼：

select * from bit b LEFT JOIN bit_reaction br ON (br.bitId=b.id AND br.userId != 1)

這里的問題是因為br.userId不等於1，所以返回的是bit_reaction .id =2。正確的行為是它只會返回ID為2和3的位。

謝謝你的提示！

Answer 1

select b.*
from bit b
left join bit_reaction br ON br.bitId = b.id 
                         AND br.userId = 1
WHERE br.bitId is null

Answer 2

我假設您希望每個用戶都做出一點反應。 因此，更通用的答案將是...

SELECT *
FROM bit AS tBit
LEFT JOIN user AS tUser ON 1 = 1
LEFT JOIN bit_reaction AS tReaction ON tBit.id = tReaction.bitID
    AND tUser.id = tReaction.userID
WHERE tReaction.userID IS NULL