在新 CASE 中使用 CASE 的输出 (SQL)

Question

有人能告诉我如何使用 CASE 语句的输出作为 t-SQL 中下一个 CASE 语句的输入吗？

exampleTable

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

我想要一个查询 returns 所有这些，以及一个布尔值来判断它是否是出厂错误。如果使用的样本少于 10 个，则错误被认为是工厂产生的。我的想法是先用CASE做一个柱子，显示使用了多少样本，像这样：

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

然后我想使用 samplesUsed 作为另一个 CASE 的输入来创建一个名为 factoryError 的布尔值。如果 samplesUsed < 10，则为 TRUE。如何做到这一点？

Answer 1

这是一种糟糕的方法，但是如果您有一列包含样本起始数量的信息，您可以修复查询并使其变得更好....但这是一种获得您想要的东西的方法

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

输出会是这样的

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

您可以使用像这样的子查询来做到这一点，

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 并在下面继续...

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

你可以使用这个：

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

测试：

在新 CASE 中使用 CASE 的输出 (SQL)

Using output from CASE in a new CASE (SQL)

sql

tsql

case