Question

我设计了一个以下的sql查询来获取12月份完成的访问总数。

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

结果：

MonthName   TotalVisit

December    164

我可以通过在SQL SEVER 2008中编写单个查询而不使用内部查询来获得相同的结果吗？

Answer 1

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 2

在我看来，外部查询是不必要的。这应该给出相同的结果：

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)

它的工作原理是因为你的“count（）”函数实际上只是计算记录。因此count（*）和count（MonthName）之间没有区别。

Answer 3

你基本上已经在你的内部查询中完成了它。只是一些变化：

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)

如何使这个SQL查询更简单/更短？

3 个答案: