SQL Server 2008选择问题

Question

有两张桌子

Users:Id(PK int), Username(varchar (50))
Emails:Id(PK int), UserId(FK int), Subject(varchar(50)), Content(varchar(250)), SentAt(datetime)

我必须显示每个用户发送的电子邮件数量，按天分组，按当天发送的电子邮件总数排序。 我最好提供一个例子：

Date     |User       |Total
---------|-----------|-------
2012-4-5 |username1  |7
2012-4-5 |username2  |2
2012-4-2 |username1  |3
2012-3-24|username1  |12
2012-3-24|username5  |2

我试过了，但显然不起作用。

ALTER PROCEDURE spGetStatistics
AS
SELECT e.SentAt, u.Username, ( SELECT COUNT(*) FROM Emails e2 WHERE e2.SentAt=e.SentAt AND e2.UserID=u.UserID ) AS Total
FROM Emails e INNER JOIN Users u ON e.UserID=u.UserID
GROUP BY e.SentAt
ORDER BY Total

LE：

Using the solution provided by Adrian which is:

    SELECT CAST (e.SentAt AS date), u.Username,  COUNT(*) AS Total
    FROM Emails e INNER JOIN Users u ON e.UserID=u.UserID
    GROUP BY CAST (e.SentAt AS date), u.Username
    ORDER BY Total

I got this:
    Date       |User       |Total
    -----------|-----------|-------
    2012-09-08 |username1  |1
    2012-09-07 |username2  |2
    2012-09-08 |username2  |2

instead of

    Date       |User       |Total
    -----------|-----------|-------
    2012-09-08 |username2  |2
    2012-09-08 |username1  |1
    2012-09-07 |username2  |2


It seems to be working like this:
SELECT CAST (e.SentAt AS date), u.Username,  COUNT(*) AS Total
FROM Emails e INNER JOIN Users u ON e.UserID=u.UserID
GROUP BY CAST (e.SentAt AS date), u.Username
ORDER BY CAST (e.SentAt AS date) DESC, Total DESC

Answer 1

应该这样做：

SELECT 
    cast(e.SentAt as Date) [Date], 
    u.Username,
    COUNT(*) AS Total
FROM Emails e INNER JOIN Users u ON e.UserID=u.UserID
GROUP BY cast(e.SentAt as Date), u.Username
ORDER BY 3

现在，这将隐藏未发送电子邮件的用户（count = 0）。 如果要包括这些内容，则应切换到以下位置：

SELECT 
    cast(e.SentAt as Date) [Date], 
    u.Username,
    COUNT(e.Id) AS Total
FROM Users u LEFT JOIN Emails e ON e.UserID=u.UserID
GROUP BY cast(e.SentAt as Date), u.Username
ORDER BY 3

更新资料

对于所需的订单，您应该选择：

SELECT 
    cast(e.SentAt as Date) [Date], 
    u.Username,
    COUNT(*) AS Total
FROM Emails e INNER JOIN Users u ON e.UserID=u.UserID
GROUP BY cast(e.SentAt as Date), u.Username
ORDER BY cast(e.SentAt as Date), Total DESC

Answer 2

SELECT e.SentAt, u.Username, count(e.Id) AS Total
FROM Emails e
  INNER JOIN Users u ON (e.UserID = u.UserID)
GROUP BY e.SentAt, u.Username
ORDER BY Total