檢索在線用戶通過登錄和註銷記錄

Question

• 

考慮用戶日誌表如上。我將用戶的登錄或註銷操作保存到此表中。我如何檢索在線用戶和登錄時間？

Answer 1

事情是這樣的：

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

我認爲這應該爲你工作：

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'; 

通過用戶名和排序最後動作只是時間分割你的表 - 如果它是Enter，那麼他就必須在線。