带有 CASE 的 WHERE 条件

Question

参考粗体部分，基本上有产品代码，并在案例说明中添加产品的合格年龄。所以下面我们有年龄为 18 岁或 14 岁的产品来使用产品。创建了一个新列作为“资格”

现在提到第二个粗体部分，我只想要“资格”>“AgeAtOpenDate”的账户，即账户持有人对于账户来说太年轻了。

SELECT 
    CASE
        WHEN EOMONTH(OpenDate,0) = a.[EtlFileDate] THEN 'New Account'
        ELSE 'Existing Account'
        END AS 'NewAccountsInMonth'
    ,CASE
        **WHEN a.[ProductCode] in (801,802) THEN '18'
        WHEN a.[ProductCode] in (480,481,489,490) THEN '14'
        END as 'Eligibility'**
    ,a.[EtlFileDate]
    ,a.[AccountNumber]
    ,a.[OpenDate] 
    ,a.[ProductCode]
    ,a.[ProductName]  
    ,a.[PrimaryCAN]
    ,b.[Cust_Age]
    ,b.[Cust_BirthDate]
    ,**(DATEDIFF(year,b.[Cust_BirthDate],a.[OpenDate] ) as 'AgeAtOpenDate'**
FROM Histaccounts a
join Marketable b
    on a.[PrimaryCAN]=b.[CAN]
**where 'Eligibility'>'AgeAtOpenDate'**
    and a.[EtlFileDate] between '2021-10-31' and '2023-03-23' 
    and a.[ProductCode] in (480,481,489,490,802,801)

当我运行上面的脚本时，我仍然得到所有结果，而不是未满年龄的结果。

我做错了什么？这是否与您不能在 SELECT 区域中使用基于 CASE 的 WHERE 条件有关？

Answer 1

问题是您不能在 SELECT 语句中定义的 WHERE 子句中使用别名。 WHERE 子句在 SELECT 语句之前求值，因此别名

Eligibility

和

AgeAtOpenDate

在 WHERE 子句中不被识别。

您可以这样重写您的查询：

SELECT *
FROM (
    SELECT 
        CASE
            WHEN EOMONTH(OpenDate,0) = a.[EtlFileDate] THEN 'New Account'
            ELSE 'Existing Account'
        END AS 'NewAccountsInMonth',
        CASE
            WHEN a.[ProductCode] in (801,802) THEN '18'
            WHEN a.[ProductCode] in (480,481,489,490) THEN '14'
        END as 'Eligibility',
        a.[EtlFileDate],
        a.[AccountNumber],
        a.[OpenDate],
        a.[ProductCode],
        a.[ProductName],
        a.[PrimaryCAN],
        b.[Cust_Age],
        b.[Cust_BirthDate],
        DATEDIFF(year,b.[Cust_BirthDate],a.[OpenDate] ) as 'AgeAtOpenDate'
    FROM Histaccounts a
    JOIN Marketable b
    ON a.[PrimaryCAN]=b.[CAN]
    WHERE a.[EtlFileDate] BETWEEN '2021-10-31' AND '2023-03-23' 
        AND a.[ProductCode] IN (480,481,489,490,802,801)
) subquery
WHERE subquery.Eligibility > subquery.AgeAtOpenDate

Answer 2

这里有几个问题，但最大的是

'Eligibility'

子句中的值

'AgeAtOpenDate'

和

WHERE

被解释为字符串文字，而不是对列别名的引用，并且由于

E

大于

A 

条件总是成功。

您可以通过多种方式解决此问题，但在这种情况下，您最好不要重复

CASE

表达式。做exactly，SQL Server足够聪明，知道

SELECT

和

WHERE

子句中的表达式是相同的，只会计算一次。任何类型的嵌套或分层，您都有可能失去对可能有助于查询的索引的使用。

Answer 3

你能尝试用整个逻辑替换 in where 子句吗

where (CASE WHEN a.[ProductCode] in (801,802) THEN '18'
WHEN a.[ProductCode] in (480,481,489,490) THEN '14'
END > (DATEDIFF(year,b.[Cust_BirthDate],a.[OpenDate] > (DATEDIFF(year,b.[Cust_BirthDate],a.[OpenDate] )) > (DATEDIFF(year,b.[Cust_BirthDate],a.[OpenDate] )) and a.[EtlFileDate] between '2021-10-31' and '2023-03-23' and a.[ProductCode] in (480,481,489,490,802,801)

Answer 4

您可以在临时表中插入记录，然后应用过滤器

SELECT 
CASE
WHEN EOMONTH(OpenDate,0) = a.[EtlFileDate] THEN 'New Account'
ELSE 'Existing Account'
END AS 'NewAccountsInMonth'
,CASE WHEN a.[ProductCode] in (801,802) THEN '18'
WHEN a.[ProductCode] in (480,481,489,490) THEN '14'
END as 'Eligibility'
,a.[EtlFileDate]
,a.[AccountNumber]
,a.[OpenDate] 
,a.[ProductCode]
,a.[ProductName]  
,a.[PrimaryCAN]
,b.[Cust_Age]
,b.[Cust_BirthDate]
,(DATEDIFF(year,b.[Cust_BirthDate],a.[OpenDate] ) as [AgeAtOpenDate]
into #Test
FROM Histaccounts a
join Marketable b
on a.[PrimaryCAN]=b.[CAN]
WHERE a.[EtlFileDate] between '2021-10-31' and '2023-03-23' and a.[ProductCode] in (480,481,489,490,802,801)

SELECT * from #Test
WHERE Eligibility>AgeAtOpenDate

CTE

WITH CTE AS
(
SELECT 
CASE
WHEN EOMONTH(OpenDate,0) = a.[EtlFileDate] THEN 'New Account'
ELSE 'Existing Account'
END AS 'NewAccountsInMonth'
,CASE WHEN a.[ProductCode] in (801,802) THEN '18'
WHEN a.[ProductCode] in (480,481,489,490) THEN '14'
END as 'Eligibility'
,a.[EtlFileDate]
,a.[AccountNumber]
,a.[OpenDate] 
,a.[ProductCode]
,a.[ProductName]  
,a.[PrimaryCAN]
,b.[Cust_Age]
,b.[Cust_BirthDate]
,(DATEDIFF(year,b.[Cust_BirthDate],a.[OpenDate] ) as [AgeAtOpenDate]
into #Test
FROM Histaccounts a
join Marketable b
on a.[PrimaryCAN]=b.[CAN]
WHERE a.[EtlFileDate] between '2021-10-31' and '2023-03-23' and a.[ProductCode] in (480,481,489,490,802,801)
)
SELECT * from CTE
WHERE Eligibility>AgeAtOpenDate