Question

我有这个SQL查询：

SELECT 
    us.userid, 
    us.username, 
    CONVERT(VARCHAR(10), s.created, 101) AS LastLoginDate 
FROM
    users us 
INNER JOIN 
    session s ON us.userid = s.userid 
WHERE  
    supergroupid = 145577 
ORDER BY 
    us.userid DESC

现在，由于每个用户在会话表中有多个会话条目，因此每个用户获得多个（重复）结果。

如何从每个用户获取会话表中最新创建的条目，如何仅从用户表中获取一个条目以及其他数据？

Answer 1

已被问及回答了数百次。但是，编写解决方案的代码比找到重复的代码容易。另外，您实际上不应该在查询中设置日期格式。这应该在表示层中完成。

select *
from
(
    SELECT us.userId, us.userName, CONVERT(VARCHAR(10),s.created, 101) as LastLoginDate
        , RowNum = ROW_NUMBER() over (partition by us.userId order by s.created desc)
      FROM users us
    inner join session s 
      on us.userId = s.userId
      where superGroupId = 145577
) x
where x.RowNum = 1
order by x.userid desc

Answer 2

我认为在日期上具有Max（）的Group By会起作用：

SELECT us.userId, us.userName, MAX(CONVERT(VARCHAR(10),s.created, 101)) as LastLoginDate
  FROM users us
inner join session s 
  on us.userId = s.userId
  where superGroupId = 145577
  group by us.userId, us.userName
  order by us.userid desc

Answer 3

您可以执行一个子查询，该子查询返回每个用户的最新会话并像这样加入：

SELECT us.userId, us.userName, CONVERT(VARCHAR(10),s.created, 101) as LastLoginDate
FROM users us
INNER JOIN
(
    SELECT s.userId, s.created, ROW_NUMBER OVER(PARTITION BY s.userId ORDER BY s.created DESC) AS [RowNum]
    FROM session AS s


) s 
  on us.userId = s.userId
  where superGroupId = 145577 AND s.[RowNum] = 1
  order by us.userid desc

Answer 4

如果要使用最近会话的日期/时间，请使用max()。但是之前转换为字符串！

select us.userId, us.userName, convert(varchar(10), max(s.created), 101) as LastLoginDate
from users us inner join
     session s 
     on us.userId = s.userId
where superGroupId = 145577
group by us.userid, us.userName;

Answer 5

使用此查询：

SELECT userId, MAX(created) as LastLoginDate
FROM session
GROUP BY userId

您将获得每个用户的最后登录日期。
然后将其连接到表users：

SELECT us.userId, us.userName, CONVERT(VARCHAR(10), s.LastLoginDate, 101) as LastLoginDate
FROM users us INNER JOIN (
    SELECT userId, MAX(created) as LastLoginDate
    FROM session
    GROUP BY userId 
) s on s.userId = us.userId 
WHERE superGroupId = 145577
ORDER BY us.userid desc

Answer 6

由于没有人提及它，所以我真的很喜欢使用公用表表达式（CTE），我认为这有助于提高可读性。

;WITH ctelastlogin (userid, lastlogindate) 
     AS (SELECT userid, 
                Max(created) 
         FROM   session 
         GROUP  BY userid) 
SELECT us.userid, 
       us.username, 
       CONVERT(VARCHAR(10), cte.lastlogindate, 101) AS LastLoginDate 
FROM   users us 
       INNER JOIN ctelastlogin cte 
               ON cte.userid = us.userid 
WHERE  supergroupid = 145577 
ORDER  BY us.userid DESC

Answer 7

您可以rank进行每个会话，然后根据最新的会话进行过滤。

类似...

SELECT * FROM (
SELECT DENSE_RANK() OVER (PARTITION BY US.USERID ORDER BY LASTLOGINDATE DESC) RNK
)
WHERE RNK = 1

具有内部联接的SQL Server返回的结果超出预期

7 个答案: