如何在同一个select语句中使用条件列值？

I have something like

我有类似的东西

(COMPLEX_EXPRESSION_N stands for a long subquery)

(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

Is it possible to use FirstCheck, SecondCheck, ThirdCheck as I did in the AllChecksOk line?

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

I am not concerned about performance, this is something that is manually run once a day on a very small number of records, I just want to avoid to create views, tables or temporary tables and keep all in a single select statement.

我不关心性能,这是每天在非常少量的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。

As an altenrative I can do this, but it makes the query less readable (as I need to write twice every complex expression):

作为一个altenrative,我可以做到这一点,但它使查询的可读性降低(因为我需要在每个复杂的表达式中写两次):

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

2 个解决方案

#1

You can't reference a column alias in the select but you can use a CTE as below.

您无法在select中引用列别名,但可以使用CTE,如下所示。

;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

You can also use CROSS APPLY to define the 3 column aliases then reference them in the main SELECT list as in this example.

您还可以使用CROSS APPLY来定义3列别名,然后在主SELECT列表中引用它们,如本例所示。

#2

Below is a derived table solution

下面是派生表解决方案

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

#1