SQL Server 2008中选择问题

Question

有两个表

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

我一定要显示多少个电邮每个用户，按天进行分组，以便通过电子邮件总数发送的那一天。 我最好还是提供了一个例子：

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，但显然是行不通的。

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

这应该这样做：

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，这个隐藏谁送没有电子邮件的用户（计数= 0）。如果要包括那些，你应该切换到这一点：

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

对于所需的顺序，你应该去：

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