Question

我想在A列中选择最大值。现在，我在A列中有多个最大值。如何使用最大值取1行并去除其余部分？我尝试使用distinct和limit 1但没有成功。

预期：只有2行，1有消息“srth”，另一行有“the-same-ts-1”或“the-same-ts-2”但不是两者都有，因为他们有相同的最大值1413588888

我的查询：

SELECT A.*, DU.user as username, DU.thumbnail 
            FROM DB_CHATS A
            INNER JOIN (
               SELECT distinct max(timestamp) TS, user, partner
               FROM db_chats
               GROUP BY  user,partner ) T
              on A.TimeStamp=T.TS 
             and A.user=T.User
            LEFT JOIN  db_users DU on t.partner = DU.id
where A.user = 'utQ8YDxD6kSrlI5QtFOUAE4h'

小提琴：sqlfiddle

Answer 1

如果您不关心哪个行返回了最长时间戳，则可以在查询结尾添加group by user, partner, timestamp。

SELECT A.*, DU.user as username, DU.thumbnail 
            FROM DB_CHATS A
            INNER JOIN (
               SELECT distinct max(timestamp) TS, user, partner
               FROM db_chats
               GROUP BY  user,partner ) T
              on A.TimeStamp=T.TS 
             and A.user=T.User
            LEFT JOIN  db_users DU on t.partner = DU.id
where A.user = 'utQ8YDxD6kSrlI5QtFOUAE4h'
group by user, partner, timestamp

http://sqlfiddle.com/#!2/efe6e/2

多个最大值时仅选择1行

1 个答案: