Question

我有类似

的东西

（COMPLEX_EXPRESSION_N代表一个长子查询）

select
  ID_Operation,
  FirstCheck = CASE WHEN (COMPLEX_EXPRESSION_1)= 0 then 0 else 1 end,
  SecondCheck = CASE WHEN (COMPLEX_EXPRESSION_2)= 0 then 0 else 1 end,
  ThirdCheck = CASE WHEN (COMPLEX_EXPRESSION_3)= 0 then 0 else 1 end,
  AllChecksOk = Case WHEN 
               (FirstCheck + SecondCheck + Third CHeck = 3) 
               Then 'OK' Else 'No' End
from 
  AllOperationsTable

是否可以像在AllChecksOk系列中那样使用FirstCheck，SecondCheck，ThirdCheck？

我不关心性能，这是每天在极少数记录上手动运行的东西，我只是想避免创建视图，表或临时表并将所有内容保存在单个select语句中。

作为一种有效的方法，我可以这样做，但它使查询的可读性降低（因为我需要为每个复杂的表达式编写两次）：

select
  ID_Operation,
  FirstCheck = CASE WHEN (COMPLEX_EXPRESSION_1)= 0 then 0 else 1 end,
  SecondCheck = CASE WHEN (COMPLEX_EXPRESSION_2)= 0 then 0 else 1 end,
  ThirdCheck = CASE WHEN (COMPLEX_EXPRESSION_3)= 0 then 0 else 1 end,
  AllChecksOk = Case WHEN 
               (COMPLEX_EXPRESSION_1+ COMPLEX_EXPRESSION_2+ 
               COMPLEX_EXPRESSION_3CHeck = 3) Then 'OK' Else 'No' End
from 
  AllOperationsTable

Answer 1

您无法在select中引用列别名，但您可以使用以下CTE。

;WITH CTE AS
(
select
  ID_Operation,
  FirstCheck = CASE WHEN (COMPLEX_EXPRESSION_1)= 0 then 0 else 1 end,
  SecondCheck = CASE WHEN (COMPLEX_EXPRESSION_2)= 0 then 0 else 1 end,
  ThirdCheck = CASE WHEN (COMPLEX_EXPRESSION_3)= 0 then 0 else 1 end
from 
  AllOperationsTable
)
SELECT *,
       AllChecksOk = Case WHEN 
               (COMPLEX_EXPRESSION_1+ COMPLEX_EXPRESSION_2+ 
               COMPLEX_EXPRESSION_3CHeck = 3) Then 'OK' Else 'No' End
FROM CTE

您还可以使用CROSS APPLY定义3列别名，然后在主SELECT列表as in this example中引用它们。

Answer 2

以下是派生表解决方案

SELECT
  T.ID_Operation,
  FirstCheck   = CASE WHEN T.Expr1 = 0 THEN 0 ELSE 1 END,
  SecondCheck  = CASE WHEN T.Expr2 = 0 THEN 0 ELSE 1 END,
  ThirdCheck   = CASE WHEN T.Expr3 = 0 THEN 0 ELSE 1 END,
  AllChecksOk  = CASE WHEN T.Expr1 + T.Expr2 + T.Expr3 = 3 THEN 'OK' ELSE 'No' END
FROM
(
  SELECT
    ID_Operation,
    Expr1 = (COMPLEX_EXPRESSION_1),
    Expr2 = (COMPLEX_EXPRESSION_2),
    Expr3 = (COMPLEX_EXPRESSION_3)
  FROM 
    AllOperationsTable
) T

如何在同一个select语句中使用条件列值？

2 个答案: