sql中的case语句使用同一语句中的其他选定列

问题描述

| 我想知道在sql Server 2005中是否可以进行以下操作。列A和B是在我的实际存储过程中使用其他case语句计算的。我不想不必要地在其他字段重复相同的内容。如果这在语法上不可行，还有其他想法吗？

SELECT A,B,CASE WHEN column1=\'1\' THEN A ELSE B END Col1.

根据要求提供的实际查询的修改版本。在这种模式下，CTE似乎很难。 WANNABE是我要在sub select语句中完成的列。

SELECT 1 AS Region,\'Test\',CAST(Work AS NUMERIC(18,2)) Work,Work + 2 AS Work2,WANNABE

        FROM
        (
            SELECT 
                ROW_NUMBER() OVER(PARTITION BY G.Value,C.C,FR.Mod1 ORDER BY FR.Date DESC,FG.Date DESC,FC.Date DESC) ROW,CASE WHEN COALESCE(FR.Mod1,\'\') = \'\' THEN \'\' ELSE FR.Mod1 END Mod1,CASE WHEN @var1=1 AND @var2 = 1 THEN FR.Col1 *  G.Value 
                     WHEN @var1=1 AND @var2 = 0 THEN FP.Col1 *  G.Value END Work,CASE WHEN 1=1 THEN Work ELSE 1 END WANNABE,(
                    SELECT Col3
                    FROM Table2 
                    WHERE c = FR.Value
                ) AS Custom

            FROM MainTable FR
            JOIN @C C ON FR.Col2 = C.Col2
            LEFT JOIN Function1(@VersionDate) cv ON cv.Code = C.Code    
            LEFT JOIN Function2(@VersionDate) hv ON hv.Code = C.Code    
            LEFT JOIN @G G ON 1 = 1
            LEFT JOIN SubTable1 FG ON FG.Number = G.Value,2 AND FG.Date = @VersionDate
            LEFT JOIN SubTable2 FO ON FO.Number = G.Value
                AND FO.Date = @VersionDate AND FO.Code = FR.Code AND FR.Mod1 = FO.Mod1
            LEFT JOIN SubTable3 FP ON FP.Code = FR.Code AND FP.VersionDate = @Versiondate
             AND CASE WHEN DATALENGTH(FR.Mod1) = 0 THEN \'00\' ELSE FR.Mod1 END = CASE WHEN DATALENGTH(FP.Mod1) = 0 THEN \'00\' ELSE FP.Mod1 END
            LEFT JOIN SubTable4 FC ON FC.Date = @VersionDate
            WHERE  FR.Date = @VersionDate 
        ) x
        WHERE x.Row = 1
        AND RTRIM(LTRIM(x.Col1)) IN (\'\',\'2\')

    

解决方法

您可以在CTE中定义“ 2”列别名，然后在外部选择中引用它们。

;WITH CTE AS
(
SELECT CASE ... END AS A,CASE ... END  AS B,column1
FROM your_table
)
SELECT A,B,CASE WHEN column1=\'1\' THEN A ELSE B END Col1
FROM  CTE 

同样，您也可以用ѭ4define定义它们，有时会有些冗长。 一个仅显示语法的愚蠢示例是

SELECT A,CASE WHEN type=\'P\' THEN A ELSE B END Col1 
FROM master..spt_values
CROSS APPLY (SELECT CASE WHEN number %2 = 1 THEN 1 END,CASE WHEN number %2 = 0 THEN 0 END) T(A,B)

更新之后，您可以将派生表替换为CTE并嵌套CTE，如下所示

;WITH x as
(
                SELECT 
                    ROW_NUMBER() OVER(PARTITION BY G.Value,C.Code,FR.Mod1 ORDER BY FR.Date DESC,FG.Date DESC,FC.Date DESC) ROW,...<snip>                
                WHERE  FR.Date = @VersionDate 
),x2 As
(
SELECT *,CASE WHEN 1=1 THEN Work ELSE 1 END WANNABE
FROM x
)
    SELECT 1 AS Region,\'Test\',CAST(Work AS NUMERIC(18,2)) Work,Work + 2 AS Work2,WANNABE
            FROM x2
            WHERE x2.Row = 1
            AND RTRIM(LTRIM(x2.Col1)) IN (\'\',\'2\')

    ,是的，这是可能的，但是您的所有sql语句如何？您可以在使用时在select语句中使用case语句。 像这样

SELECT SUM((CASE WHEN column1=\'1\' THEN 10 ELSE 0 END)) AS A,SUM((CASE WHEN column1=\'2\' THEN 10 ELSE 0 END)) AS B
FROM YourTable