如何通过派生列

Question

组我有这样的SQL：

Select Hours, LastName, FirstName, UUID, 
     Case 
     When DatePart(WeekDay, Date) = 1 Then 
      Date - 6 
     Else 
      Date - DatePart(Weekday, Date) + 2 
     End as [Week] 
    From Entry 
    Where Date between '06/30/2014' and '10/31/2014' 

，我想要做什么是由[周]列，我使用Case语句创建的组这一点。这是可能的吗？如果是这样，我该怎么做呢？

谢谢！

Answer 1

我猜你正在努力寻找一个员工的小时max or sum。所以这样的事情应该可以帮到你。请记住，没有聚合函数的列应该出现在group by中。

SELECT Max(Hours),-- sum(Hours) 
     LastName, 
     FirstName, 
     UUID, 
     CASE 
     WHEN Datepart(WeekDay, Date) = 1 THEN Date - 6 
     ELSE Date - Datepart(Weekday, Date) + 2 
     END AS [Week] 
FROM Entry 
WHERE Date BETWEEN '06/30/2014' AND '10/31/2014' 
GROUP BY LastName, 
      FirstName, 
      UUID, 
      CASE 
      WHEN Datepart(WeekDay, Date) = 1 THEN Date - 6 
      ELSE Date - Datepart(Weekday, Date) + 2 
      END 

Answer 2

您不能在SQL Server中的列别名组 - 你需要一群以表达：

Select Hours, LastName, FirstName, UUID, 
    Case 
    When DatePart(WeekDay, Date) = 1 Then 
     Date - 6 
    Else 
     Date - DatePart(Weekday, Date) + 2 
    End as [Week] 
From Entry 
Where Date between '06/30/2014' and '10/31/2014' 
GROUP BY 
    Case 
    When DatePart(WeekDay, Date) = 1 Then 
     Date - 6 
    Else 
     Date - DatePart(Weekday, Date) + 2 
    End 

虽然你可以使用子查询使它有点清洁：

SELECT * FROM 
    (
    Select Hours, LastName, FirstName, UUID, 
     Case 
     When DatePart(WeekDay, Date) = 1 Then 
      Date - 6 
     Else 
      Date - DatePart(Weekday, Date) + 2 
     End as [Week] 
    From Entry 
    Where Date between '06/30/2014' and '10/31/2014' 
    ) 
    GROUP BY [Week] 

但是在任何情况下，您都需要决定如何在组表达式中集合而不是的值。 Hours有意义做一笔款项，但您如何汇总名称和ID？如果没有聚集是必要的只是让他们出来的结果：

SELECT Week, SUM(Hours) FROM 
    (
    Select Hours, LastName, FirstName, UUID, 
     Case 
     When DatePart(WeekDay, Date) = 1 Then 
      Date - 6 
     Else 
      Date - DatePart(Weekday, Date) + 2 
     End as [Week] 
    From Entry 
    Where Date between '06/30/2014' and '10/31/2014' 
    ) 
    GROUP BY [Week]