Question

我可以在同一视图中使用稍后在SQL Server视图中计算的列吗？

假设我有以下观点：

Select 
    t1.StartMile, t2.EndMile,  t2.EndMile- t1.StartMile as TotMile
from 
   TableStarts as t1 
inner join 
   TableEnds as t2 on t1.Id = t2.Id

有没有办法编辑视图以执行以下操作

Select  
    t1.StartMile, t2.EndMile, t2.EndMile - t1.StartMile as TotMile, 
    TotMile + 30  as EvenMoreMiles

我试过这个并收到错误：

无效的列名称“TotMile”

请不要告诉我使用t2.EndMile - t1.StartMile + 30 as EvenMoreMiles。 TotMiles是我实际代码中的长例语句。

我宁愿不必创建中间视图。

我正在使用SQL Server 2005。

稍后添加

感谢所有答案。我会全力以赴。

答案提出了以下新问题：

鉴于有数千行，TotMiles如下所示，给出的答案中哪一个最有效？或者创建中间视图是否最有效？

CASE WHEN t .TaskType = 1  and  t .StartTime < '1/1/2012'  
               THEN (tv.EndMile - tv.StartMile )  
     WHEN NOT (t .Location1_PKey = c.pkey OR t .Location2_PKey = c.pkey)
              then (tv.EndMile - tv.StartMile )
     WHEN (tv.EndMile - tv.StartMile ) < 31  Then 0 
     ELSE  (tv.EndMile - tv.StartMile - 30 )
END AS MilesAdjusted2012,

Answer 1

您还可以使用CROSS APPLY，这可能更简洁，特别是如果您正在构建引用前面的别名链。

SELECT t1.StartMile,
       t2.EndMile,
       TotMile,
       EvenMoreMiles,
       AndYetMoreMiles
FROM   TableStarts AS t1
       INNER JOIN TableEnds AS t2
         ON t1.Id = t2.Id
       CROSS APPLY (SELECT t2.EndMile - t1.StartMile) A(TotMile)
       CROSS APPLY (SELECT TotMile + 30) A2(EvenMoreMiles)
       CROSS APPLY (SELECT EvenMoreMiles + 100) A3(AndYetMoreMiles)

Answer 2

你不能直接，但你可以建立子选择：

select StartMile,EndMile,TotMile,TotMile+30 as EvenMoreMiles from (
  Select t1.StartMile, t2.EndMile,  t2.EndMile- t1.StartMile as TotMile
  from 
  TableStarts as t1 
  inner join 
  TableEnds as t2 
  on t1.Id = t2.Id  
) t

或使用公用表格表达式：

;with FirstCalcs as (
  Select t1.StartMile, t2.EndMile,  t2.EndMile- t1.StartMile as TotMile
  from 
  TableStarts as t1 
  inner join 
  TableEnds as t2 
  on t1.Id = t2.Id  
)
select StartMile,EndMile,TotMile,TotMile+30 as EvenMoreMiles from FirstCalcs

如果会有多个级别构建最终计算，我通常更喜欢使用CTE，因为否则大多数格式化方案很难做出选择，子选择，子子选择等等，这很容易阅读。 CTE可以包括对先前定义的CTE的引用：

;with CTE1 as (
    SELECT ...
), CTE2 as (
    SELECT ... FROM CTE1
), CTE3 as (
    SELECT ... FROM CTE2
), CTE4 as (
    SELECT ... FROM CTE2 ... CTE3
)
SELECT ... FROM CTE4 ... CTE1

Answer 3

尝试使用派生表。

SELECT 
  DerivedTable.*,
  TotMile + 30 as EvenMoreMiles
From (Select 
        t1.StartMile, 
        t2.EndMile, 
        t2.EndMile- t1.StartMile as TotMile
        FROM Table t1 
        Inner Join table2 t2 on t1.PK = t2.FK) DerivedTable

Answer 4

您可以使用公用表表达式（CTE）执行此操作。这里有很多：http://www.4guysfromrolla.com/webtech/071906-1.shtml

基本上，

CREATE VIEW ... AS

WITH Mileage (StartMile, EndMile, TotMile) AS (Select t1.StartMile, t2.EndMile,  t2.EndMile- t1.StartMile as TotMile
from 
TableStarts as t1 
inner join 
TableEnds as t2 
on t1.Id = t2.Id) 

SELECT TotMile FROM Mileage

我可以在同一视图中使用稍后在SQL Server视图中计算的列吗？

4 个答案: