MySQL的選擇不同用戶

Question

我有一個表結構，其中我把發送的消息記錄的最近傳入或傳出消息和下面一樣接受;

member_id1是發送者和member_id2爲接收端。

現在我想要實現的是獲取具有member_id爲3的用戶的最近消息的行。結果應該只包含2行，消息ID爲2和4，爲2是member_id爲3的用戶與member_id爲2的用戶之間的最後一條消息，4是member_id爲3的用戶與member_id爲1的用戶之間的唯一消息。

結果不應該包含message_id爲3的行，因爲它與member_id爲3的用戶沒有任何關係，並且message_id爲1，因爲它已由具有message_id的message_id的消息過期2.

希望我做了清楚我的問題的人誰可以幫我解決這個問題。

Answer 1

我想我已經找到了適合自己的問題的正確答案。雖然我不太清楚，但它似乎很好。對於需要解決此類問題的人員;試試這個：

SELECT m1.* 
    FROM table_name m1 
    INNER JOIN (SELECT MAX(senddate) AS senddate, 
        IF(member_id2 = 3, member_id1, member_id2) AS user 
       FROM table_name 
       WHERE (member_id1 = 3 AND delete1=0) OR 
        (member_id2 = 3 AND delete2=0) 
       GROUP BY user) m2 
     ON m1.senddate = m2.senddate AND 
      (m1.member_id1 = m2.user OR m1.member_id2 = m2.user) 
    WHERE (member_id1 = 3 AND delete1=0) OR 
      (member_id2 = 3 AND delete2=0) 
    ORDER BY m1.senddate DESC 

Answer 2

的問題是有點模糊，但是從我瞭解你在找這個？

SELECT * FROM table_name WHERE member_id2 = 3 ORDER BY senddate DESC; 

Answer 3

你可以使用UNION將它們合併

(SELECT * FROM table_name WHERE member_id2 = 3 ORDER BY senddate DESC limit 1) 
union 
(SELECT * FROM table_name WHERE member_id1 = 3 ORDER BY senddate DESC limit 1) 

，或者如果你需要獲得最新的已發送/爲每個成員收到，你可以內部聯接的查詢獲取最大senddate每個：

select * from table_name t1 inner join 
(
select member_id1, null as member_id2, max(senddate) as senddate 
from table_name group by member_id1 
UNION 
select null as member_id1, member_id2, max(senddate) as senddate 
from table_name group by member_id2 
) r ON (t1.member_id1 = r.member_id1 OR t1.member_id2 = r.member_id2) 
AND t1.senddate = r.senddate