Question

在以下示例数据中，我需要选择

所有记录

ModelOut=ModelOut（全部）
ModelIn<>ModelOut
ModelIn=ModelOut

问题是ModelIn<>ModelOut，因为我不知道怎么用where子句中的CASE语句来做。

Declare @type int;
SET @type=2; --- ModelIn <> ModelOut  

Create table #Data(ID int, ModelIn varchar(10), ModelOut varchar(10))
INSERT INTO #Data
    SELECT 1 AS ID,'A' AS ModelIn, 'B' AS ModelOut
    UNION ALL 
    SELECT 2 AS ID,'B' AS ModelIn, 'B' AS ModelOut
    UNION ALL 
    SELECT 3 AS ID,'C' AS ModelIn, 'D' AS ModelOut
    UNION ALL 
    SELECT 4 AS ID,'D' AS ModelIn, 'D' AS ModelOut

SELECT * FROM #Data
WHERE ModelOut =
    CASE  @type
        WHEN 1 THEN ModelOut --- all
        WHEN 2 THEN ???      --- ModelIn <> ModelOut
        WHEN 3 THEN ModelIn  --- ModelOut = ModelIn
    END
;

Drop table #Data;

Answer 1

您的查询不需要CASE（事实上，这只会使这里的事情变得复杂，我会说）。只需写下这样的查询：

SELECT * FROM #Data
WHERE (
    @type = 1 OR
   (@type = 2 AND (ModelIn <> ModelOut)) OR
   (@type = 3 AND (ModelOut = ModelIn))
);

Answer 2

作为一个案例，你可以再做一次CASE。如果您提供的WHERE子句不是更强制查询的简化方差 - 我会使用nyarlathotep建议的方法和重构的WHERE子句。

 WHERE ModelOut =
        CASE  @type
            WHEN 1 THEN ModelOut --- all
            WHEN 2 THEN 
                       CASE WHEN ModelIn <> ModelOut THEN ModelOut
                            ELSE ModelOut  + '_'
                       END
            WHEN 3 THEN ModelIn  --- ModelOut = ModelIn
        END

所以当ModelIn <> ModelOut时 - 整个CASE将返回true，否则为false

Answer 3

you should change your select query in this way

Declare @type int;
    SET @type=2; 
    SELECT * FROM #Data
    WHERE (@type = 1 )
    union
    SELECT * FROM #Data
    WHERE  (@type = 2 AND (ModelIn <> ModelOut)) 
      union 
      SELECT * FROM #Data
    WHERE    
          (@type = 3 AND (ModelOut = ModelIn))

可能会有所帮助

带有Col1＆lt;＆gt; Col2的where子句中的CASE

3 个答案: