sql 2005 case 语句 - 列名无效答案

【问题标题】：sql 2005 case statement - Invalid Column Namesql 2005 case 语句 - 列名无效
【发布时间】：2009-06-23 15:12:45
【问题描述】：

谁能告诉我为什么会出错：消息 207，级别 16，状态 1，过程 ExtractPDP4FromPDP，第 21 行列名“ContainsEX”无效。

执行以下存储过程时。

CREATE PROCEDURE ExtractPDP4FromPDP 
    -- Add the parameters for the stored procedure here
AS
BEGIN

-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;

-- Insert statements for procedure here
SELECT PDP.*, LEFT(PDPCode,7) AS PDP7, PDP.Obsolete, 
        PDP.InvestorPDP, PDP.OnlineReport, PDP.ClientSpecific, 
        ContainsEX = CASE 
    WHEN(CHARINDEX(Left(PDPCode,5),'EX')>0) THEN 'True'
    ELSE 'False'
END, PDP4 =
CASE 
    WHEN ContainsEX = 'True' THEN 'E' & SUBSTRING(pdpcode,5,3)
    ELSE SUBSTRING(pdpcode,6,3)
END
FROM PDP
WHERE (((PDP.Obsolete)='False') AND ((PDP.InvestorPDP)='True') AND 
    ((PDP.OnlineReport)='False') AND ((PDP.ClientSpecific)='False'));  
END
GO

提前谢谢你

【问题讨论】：

标签： sql database sql-server-2005

【解决方案1】：

Sql Server 不允许您引用同一级别的字段。您必须创建一个子查询，例如：

select *,
    PDP4 = CASE 
        WHEN ContainsEX = 'True' THEN 'E' & SUBSTRING(pdpcode,5,3)
        ELSE SUBSTRING(pdpcode,6,3)
    END
from (
    select *, LEFT(PDPCode,7) AS PDP7, PDP.Obsolete, 
        PDP.InvestorPDP, PDP.OnlineReport, PDP.ClientSpecific, 
        ContainsEX = CASE 
            WHEN(CHARINDEX(Left(PDPCode,5),'EX')>0) THEN 'True'
            ELSE 'False'
        END
    from PDP
    WHERE (((PDP.Obsolete)='False') AND ((PDP.InvestorPDP)='True') AND 
   ((PDP.OnlineReport)='False') AND ((PDP.ClientSpecific)='False'))
) sub

【讨论】：

【解决方案2】：

您不能在定义后立即在语句中使用列。

另一种方法是使用堆叠 CTE 来构建表达式或使用嵌套查询：

WITH cte1 AS (
    SELECT x, x AS y
    FROM t
),cte2 AS (
    SELECT x, y, x + y AS z
    FROM cte1
)
SELECT x, y, z
FROM cte2

【讨论】：

【解决方案3】：

您的案例陈述不正确。案例当“价值”=“价值”那么 '做类似 CONTAINEX = 'grandma' END

【讨论】：