在同一个选择中使用别名

Question

一旦我设置了这样的列名 SUM(someColumn) AS [ColumnName],我怎么能在之后使用它？

假设我构建了一个这样的查询:

SELECT SUM(foo.A + foo.B + foo.C + foo.D + foo.E) AS [TotalFoo],
       SUM(bar.A + bar.B + bar.C + bar.D + bar.E) AS [TotalBar],
       -- I need [TotalFooBar]

在同一个选择中我想要总和[TotalFoo]和[TotalBar].有可能参考这些专栏吗？我可以做到很久:

SELECT SUM(foo.A + foo.B + foo.C + foo.D + foo.E) AS [TotalFoo],
       SUM(bar.A + bar.B + bar.C + bar.D + bar.E) AS [TotalBar],
       SUM((foo.A + foo.B + foo.C + foo.D + foo.E) +
           (bar.A + bar.B + bar.C + bar.D + bar.E)) AS [TotalFooBar]

在这个例子中没问题,但我有更多的列,很难遵循.如果我必须使用这个列([TotalFooBar])怎么办？我每次都要重写整个SUM吗？
我正在寻找的是这样的:

SELECT SUM(foo.A + foo.B + foo.C + foo.D + foo.E) AS [TotalFoo],
       SUM(bar.A + bar.B + bar.C + bar.D + bar.E) AS [TotalBar],
       SUM([TotalFoo] + [TotalBar]) AS [TotalFooBar]

它甚至可能吗？

Answer 1

不,你不能在同一个SELECT语句中这样做,但你可以使用子查询:

SELECT 
  TotalFoo,
  TotalBar,
  TotalFoo + TotalBar AS TotalFooBar
FROM
(
    SELECT SUM(foo.A + foo.B + foo.C + foo.D + foo.E) AS [TotalFoo],
           SUM(bar.A + bar.B + bar.C + bar.D + bar.E) AS [TotalBar],
           ...
    FROM ...
) AS sub
...

或CTE:

WITH CTE
AS
(
   SELECT SUM(foo.A + foo.B + foo.C + foo.D + foo.E) AS [TotalFoo],
          SUM(bar.A + bar.B + bar.C + bar.D + bar.E) AS [TotalBar],
          ...
   FROM ...
)
SELECT 
  TotalFoo,
  TotalBar,
  TotalFoo + TotalBar AS TotalFooBar
FROM CTE