Mysql 在这种情况下，您会认为接收方不在…唯一发送方将消除这些。很高兴你找到了解决办法！现在用括号括起来怎么样（发送方=10或接收方=10）？非常感谢您抽出时间，但似乎仍然没有按预期工作。为了简化查询，我正在制作另一个表。再次感谢。。 id | sender |

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在这种情况下，您会认为

接收方不在…

唯一发送方将消除这些。很高兴你找到了解决办法！现在用括号括起来怎么样（发送方=10或接收方=10）？非常感谢您抽出时间，但似乎仍然没有按预期工作。为了简化查询，我正在制作另一个表。再次感谢。。

id  | sender |  receiver | msg
1   |   10   |    5      | hello
2       10        5         df
3       5        10         fds
4       10        7         sdf

SELECT ID, Sender, Receiver
FROM (SELECT A.*
           , Case when user1 = @user1 and user2 = @user2 then @RN:=@RN+1 else @RN:=1 end as RN
           , case when user1 = @User1 then user1 else @user1:=user1 end u1
           , case when user2 = @User2 then user2 else @user2:=user2 end u2
      FROM (SELECT ID, sender, receiver
                 , case when Sender < Receiver then Sender else Receiver end user1
                 , case when Sender > Receiver then Sender else Receiver end user2
            FROM SQLFOo) A
      cross join (Select @RN:=0, @User1:='', @user2:='') b
      ORDER BY U1, U2, ID
      ) C
WHERE RN = 1
#based on last comment is this what you mean?
# AND (Sender = 10 or receiver = 10); 

SELECT * FROM messages WHERE receiver NOT IN  
(SELECT sender FROM messages WHERE sender = 10 or receiver = 10 GROUP by sender)   
AND (sender = 10 OR receiver = 10);