SQL查找一个表中也存在于另一个表中的所有行

Question

我有以下表格：

1. UserConversation：userId和ConversationId
2. ConversationMessageReceipt：userId，conversationId，conversationMessageId和其他列
3. ConversationMessageReceipt：conversationId，conversationMessageId，userid

我可以添加更多细节，但我基本上想在一个表中找到也存在于另一个表中的行，即从第一个表中找到的所有行必须存在于另一个表中。

有没有办法找到第二个表中的所有行或获得空结果？

由于

Answer 1

尝试加入以下内容：

SELECT *
FROM UserConversation uc INNER JOIN ConvesationMessageReceipt cmr
ON  uc.userId = cmr.userId
AND uc.conversationId = cmr.conversationId

Answer 2

使用INNER JOIN你的场景，

SELECT * FROM UserConversation INNER JOIN ConvesationMessageReceipt
ON  UserConversation.userId = ConvesationMessageReceipt.userId
AND UserConversation.conversationId = ConvesationMessageReceipt.conversationId

或者你想从第一张表中获取所有记录使用LEFT JOIN或LEFT OUTER JOIN

SELECT * FROM UserConversation LEFT JOIN ConvesationMessageReceipt
ON  UserConversation.userId = ConvesationMessageReceipt.userId
AND UserConversation.conversationId = ConvesationMessageReceipt.conversationId

Answer 3

如果要检查表2中的table1数据，还可以使用EXISTS关键字..

 SELECT *
 FROM UserConversation uc
 WHERE EXISTS (SELECT 1
    FROM ConversationMessageReceipt cm
    WHERE uc.userId=cm.userid
       AND uc.conversationid=cm.conversationid)