将聚合函数应用于另一个聚合函数的SQL查询

Question

我有几个查询结果使用一个或多个聚合函数和日期GROUP-BY,所以他们看起来像这样:

Date     VisitCount(COUNT)  TotalBilling(SUM)
1/1/10     234                15765.21
1/2/10     321                23146.27
1/3/10     289                19436.51

上面简化的SQL是:

SELECT 
  VisitDate, 
  COUNT(*) AS VisitCount, 
  SUM(BilledAmount) AS TotalBilling 

FROM Visits 

GROUP BY VisitDate

我想要的是一种将聚合函数(如AVG)应用于结果集中的一列的方法.例如,我想将"AvgVisits"和"AvgBilling"列添加到结果集中,如下所示:

Date     VisitCount(COUNT)  TotalBilling(SUM)  AvgVisits  AvgBilling
1/1/10     234                15765.21          281.3      19449.33
1/2/10     321                23146.27          281.3      19449.33
1/3/10     289                19436.51          281.3      19449.33

SQL不允许将聚合函数应用于另一个聚合函数或子查询,因此我能想到的唯一方法是使用临时表或迭代结果集并手动计算值.有没有办法在没有临时表或手动计算的情况下在MSSQL2008中执行此操作？

Answer 1

with cteGrouped as (
SELECT 
  VisitDate, 
  COUNT(*) AS VisitCount, 
  SUM(BilledAmount) AS TotalBilling
FROM Visits 
GROUP BY VisitDate),
cteTotal as ( 
SELECT COUNT(*)/COUNT(DISTINCT VisitDate) as AvgVisits,
     SUM(BilledAmount)/COUNT(DISTINCT VisitDate) as AvgBilling
FROM Visits)
SELECT *
FROM cteGrouped
CROSS JOIN cteTotal;

您可以通过子查询实现相同,我只是发现CTE更具表现力.