在WHERE子句中，无效的列名错误使用CASE选择的列

Question

我有一个（非常复杂的）SQL语句，我从很多不同的表中选择数据，为了应对不良的遗留数据结构，我有一些自定义根据其他列的值获取其值的列。我已经与目前陈述CASE解决了这个：

SELECT 
    ..., 
    CASE channel 
     WHEN 1 THEN channel_1 
     WHEN 2 THEN channel_2 
     ... 
     ELSE 0 
    END AS ChannelValue, 
    CASE channelu 
     WHEN 1 THEN channelu_1 
     WHEN 2 THEN channelu_2 
     ... 
     ELSE '0' 
    END AS ChannelWithUnit, 
    ... 
FROM 
    ... 
--rest of statement continues with multiple joins and where/and clauses... 

我得到的所有执行在MS SQL Server Management Studio中查询时，列名被列为我在AS子句指定我所期望的结果。但是，由于某种原因，我不允许在WHERE语句中使用条件值。如果我在查询的末尾添加

AND ChannelValue > Limit * p.Percentage/100 

，我得到一个错误在该行称

消息207，级别16，状态1，行152
无效的列名称ChannelValue“

为什么不允许这样做？我该怎么做呢？

Answer 1

SQL语句它是有效的使用在SELECT列表中声明一个别名的只有部分是ORDER BY条款。对于查询的其他部分，您只需重复整个CASE表达式并相信优化器识别它是相同的。

如果您使用的是SQL2005 +，则可以使用CTE来避免此问题，这有助于提高可读性。

WITH YourQuery As 
(

SELECT 
    Limit, 
    Percentage, 
    CASE channel 
     WHEN 1 THEN channel_1 
     WHEN 2 THEN channel_2 
     ... 
     ELSE 0 
    END AS ChannelValue, 
    CASE channelu 
     WHEN 1 THEN channelu_1 
     WHEN 2 THEN channelu_2 
     ... 
     ELSE '0' 
    END AS ChannelWithUnit, 
    ... 
FROM 
) 

select ... 
FROM YourQuery WHERE 
ChannelValue > Limit * Percentage/100 

Answer 2

不能在同一select级别的where子句中使用ChannelValue列名。
你将不得不把这整个select在一个子查询。

select .... 
from 
( 
your select query 
) as innerSelect 
where ChannelValue > Limit * p.Percentage/100 

Answer 3

您可以使用CTE - 像

WITH CTE AS 
(
SELECT 
    ..., 
    CASE channel 
     WHEN 1 THEN channel_1 
     WHEN 2 THEN channel_2 
     ... 
     ELSE 0 
    END AS ChannelValue, 
    CASE channelu 
     WHEN 1 THEN channelu_1 
     WHEN 2 THEN channelu_2 
     ... 
     ELSE '0' 
    END AS ChannelWithUnit, 
    ... 
FROM 
) 
SELECT * 
FROM CTE 
WHERE ChannelValue > Limit * p.Percentage/100 

Answer 4

-- SOMETHING FROM ADVENTURE WORKS THIS WORKS AS THE ABOVE POSTER 
--- USING 'WITH CTE AS' 
-- MY ANSWER TO A QUERY 

WITH CTE AS 
(
SELECT HE.Gender AS [GENDER], HE.HireDate AS [HIREDATE],  HE.BirthDate AS [BIRTHDATE], 
CASE 
WHEN DATEPART(YY,[BIRTHDATE]) BETWEEN 1962 AND 1970 AND [GENDER] = 'M' AND DATEPART(YY,[HIREDATE]) > 2001 THEN 'MALE' 
WHEN DATEPART(YY,[BIRTHDATE]) BETWEEN 1972 AND 1975 AND [GENDER] = 'F' AND DATEPART(YY,[HIREDATE]) BETWEEN 2001 AND 2002 THEN 'FEMALE' 
ELSE 'NOTREQUIRED' 
END AS [RESULT] 
FROM [HumanResources].[Employee] AS HE 
) 
SELECT * 
FROM CTE 
WHERE [RESULT] <> 'NOTREQUIRED' -- GOT THIS TOO WORK NO FEMALES IN RESULT 
ORDER BY [RESULT]