我如何使這個SQL查詢更簡單/更短？

Question

我設計了一個下面的sql查詢來獲得12月份完成的訪問總數。

select q.MonthName, count(q.MonthName) as TotalVisit from 
(
SELECT DATENAME(MONTH,v.VisitDate) as MonthName  
FROM Visits v 
INNER JOIN Assignments a ON a.AssignmentID = v.AssignmentID 
WHERE a.ClientID IN (33,67) 
AND v.VisitDate BETWEEN '01/12/2013' AND '31/12/2013' 
)q 
group by q.MonthName 

結果：

MonthName TotalVisit 

December 164 

我能得到通過編寫一個查詢相同的結果，而不在SQL SEVER 2008使用內部查詢？

Answer 1

它在我看來像外部查詢是不必要的。這應該會給出相同的結果：

SELECT DATENAME(MONTH,v.VisitDate) as MonthName, count(*) as TotalVisit 
FROM Visits v 
INNER JOIN Assignments a ON a.AssignmentID = v.AssignmentID 
WHERE a.ClientID IN (33,67) 
AND v.VisitDate BETWEEN '01/12/2013' AND '31/12/2013' 
group by DATENAME(MONTH,v.VisitDate) 

它的工作原理是因爲您的「count（）」函數實際上只是計數記錄。所以count（*）和count（MonthName）之間沒有區別。

Answer 2

SELECT DATENAME(MONTH,v.VisitDate) as MonthName, 
    COUNT(*) AS TotalVisit 
FROM Visits v 
INNER JOIN Assignments a ON a.AssignmentID = v.AssignmentID 
WHERE a.ClientID IN (33,67) 
    AND v.VisitDate BETWEEN '01/12/2013' AND '31/12/2013' 
GROUP BY DATENAME(MONTH,v.VisitDate) 

Answer 3

你基本上已經完成了你的內部查詢。只是幾個變化：

SELECT DATENAME(MONTH,v.VisitDate) as MonthName 
,COUNT(v.ID) AS Visits 
FROM Visits v 
INNER JOIN Assignments a ON a.AssignmentID = v.AssignmentID 
WHERE a.ClientID IN (33,67) 
AND (v.VisitDate >= '01/12/2013' AND v.VisitDate <= '31/12/2013') --changed this for performance 
GROUP BY DATENAME(MONTH,v.VisitDate)