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Question

我有3個表：

用戶：

Id Login 
1 John 
2 Bill 
3 Jim 

電腦：

Id Name 
1 Computer1 
2 Computer2 
3 Computer3 
4 Computer4 
5 Computer5 

會議：

UserId ComputerId Minutes 
1  2   47 
2  1   32 
1  4   15 
2  5   5 
1  2   7 
1  1   40 
2  5   31 

我想顯示此結果表：

Login Total_sess Total_min Most_freq_computer Sess_on_most_freq Min_on_most_freq 
John 4   109   Computer2   2     54 
Bill 3   68   Computer5   2     36 
Jim  -   -   -     -     - 

自己，我只能滿足前3列有：

SELECT Login, COUNT(sessions.UserId), SUM(Minutes) FROM users 
LEFT JOIN sessions 
ON users.Id = sessions.UserId GROUP BY users.Id 

與某種其他列的有：

SELECT main.* 
FROM (SELECT UserId, ComputerId, COUNT(*) AS cnt ,SUM(Minutes) 
FROM sessions 
GROUP BY UserId, ComputerId) AS main 
INNER JOIN (
SELECT ComputerId, MAX(cnt) AS maxCnt FROM (
SELECT ComputerId, UserId, COUNT(*) AS cnt FROM sessions GROUP BY ComputerId, UserId 
) 
AS Counts GROUP BY ComputerId) 
        AS maxes 
ON main.ComputerId = maxes.ComputerId 
AND main.cnt = maxes.maxCnt 

但我需要在一個查詢中得到整個結果表。我覺得我在做一些完全錯誤的事情。需要幫忙。

Answer 1

給你：

SELECT u.login, t1.total_sess, t1.total_min, t2.mf, t2.sess_mf, t2.min_mf 
FROM  users u 
LEFT JOIN (
    SELECT userid, COUNT(minutes) AS total_sess, SUM(minutes) AS total_min 
    FROM  sessions 
    GROUP BY userid 
) AS t1 ON t1.userid = u.id 
LEFT JOIN (
    SELECT userid, name AS mf, COUNT(*) AS sess_mf, SUM(minutes) AS min_mf 
    FROM  sessions s 
    JOIN  computers c ON c.id = s.computerid 
    GROUP BY userid, computerid 
    HAVING COUNT(computerid) >= ALL(SELECT COUNT(*) 
            FROM  sessions s2 
            WHERE s2.userid = s.userid 
            GROUP BY s2.computerid) 
) AS t2 ON t2.userid = u.id 

我使用MySQL的語法，但它應該是相當便攜。

如果您需要更多，請隨時問！

編輯：我更新了查詢，前一個是錯誤的:(