Question

有人可以告诉我如何在t-SQL的下一个CASE语句中使用CASE语句的输出作为输入吗？

exampleTable

id | itemNo | samplesLeft
-------------------------
 1 |   001  |       104
 2 |   003  |        53
 3 |   002  |       193
 4 |   001  |        32

我想要一个返回所有这些的查询，以及一个告诉它是否是工厂生成错误的布尔值。如果使用的样本少于十个，则错误被视为工厂出生。我的想法是首先使用CASE创建一个列，显示已使用了多少样本，如下所示：

查询

SELECT
id,
itemNo,
samplesLeft,
CASE 
     WHEN itemNo= 001 
         THEN 200 - samplesLeft

         WHEN itemNo= 002
         THEN 300 - samplesLeft

         WHEN itemNo= 003
         THEN 400 - samplesLeft                     

     ELSE 100 - samplesLeft
END AS samplesUsed

FROM exampleTable

然后我想在另一个CASE中使用samplesUsed作为输入，来制作一个名为factoryError的布尔值。如果samplesUsed < 10，则说明为TRUE。怎么做？

Answer 1

这是一种不好的方法，但是如果你有一个包含起始样本数量信息的列，你可以修复查询并使其更好......但这里有一种方法可以得到你想要的东西

create table #TempTableSam (itemNo nvarchar(5), samplesLeft int)
insert into #TempTableSam (itemNo, samplesLeft)
values ('001',50),('002',10),('003',20), ('004',80)

select itemNo, samplesLeft,
case
   WHEN itemNo = '001' and 200 - samplesLeft < 190 then 'More than 10 samples has been used'
   WHEN itemNo = '002' and 300 - samplesLeft < 280 then 'More than 10 samples has been used'
   WHEN itemNo = '003' and 200 - samplesLeft < 190 then 'More than 10 samples has been used'
   WHEN itemNo = '004' and 200 - samplesLeft < 190 then 'More than 10 samples has been used'
  else 'Less then 10 samples has been used'
END as UsedSamples
from #TempTableSam

输出将是这样的

itemNo  samplesLeft          UsedSamples
 001        50       More than 10 samples has been used
 002        10       Less then 10 samples has been used
 003        20       More than 10 samples has been used
 004        80       More than 10 samples has been used

Answer 2

您可以使用子查询执行此操作，例如

select 
    x.*,
    case 
        when samplesUsed < 10 then 'Error'
        else 'right'
    end as status
from (  
    select 
        t.*,
        CASE 
            WHEN itemNo = 001 THEN 200 - samplesLeft
            WHEN itemNo = 002 THEN 300 - samplesLeft
            WHEN itemNo = 003 THEN 400 - samplesLeft
            ELSE 100 - samplesLeft
        END AS samplesUsed
    from tbl
) x

Answer 3

您可以将您的工作查询作为CTE并继续下面...

WITH YourSELECTasCTE AS
(
    SELECT
    id,
    itemNo,
    samplesLeft,
    CASE 
         WHEN itemNo= 001 
             THEN 200 - samplesLeft

             WHEN itemNo= 002
             THEN 300 - samplesLeft

             WHEN itemNo= 003
             THEN 400 - samplesLeft                     

         ELSE 100 - samplesLeft
    END AS samplesUsed

    FROM exampleTable
)
SELECT * --do whatever you want here
FROM YourSELECTasCTE

Answer 4

你可以用这个：

SELECT  id ,
        itemNo ,
        samplesLeft ,
        CASE WHEN ( CASE WHEN itemNo = '001' THEN 200 - samplesLeft
                         WHEN itemNo = '002' THEN 300 - samplesLeft
                         WHEN itemNo = '003' THEN 400 - samplesLeft
                         ELSE 100 - samplesLeft
                    END ) < 10 THEN 'factory born error'
             ELSE 'ok'
        END AS samplesUsed
FROM    exampleTable

试验：

在新CASE中使用CASE的输出（SQL）

4 个答案: