检索在线用户通过登录和注销记录

Question

• 

考虑用户日志表如上。我将用户的登录或注销操作保存到此表中。我如何检索在线用户和登录时间？

Answer 1

事情是这样的：

select * from UserLog l1 
where Operation = 'Enter' and 
     not exists(select * from UserLog l2 
       where l1.user = l2.user and 
         l2.Operation = 'Exit' and 
         l2.Time > l1.Time) 

Answer 2

我认为这应该为你工作：

SELECT * 
FROM (
    SELECT ROW_NUMBER() OVER (PARTITION BY UL.id ORDER BY UL.Time DESC) AS RN, UL.* 
    FROM dbo.UserLog AS UL 
    ) AS T 
WHERE T.RN = 1 
    AND T.Operation = 'Enter'; 

通过用户名和排序最后动作只是时间分割你的表 - 如果它是Enter，那么他就必须在线。