注意Transact-SQL中Case函数的两种用法导致不同的结果集

SELECT  A.GCMC AS FNAME,A.JSDW AS FOWNER,case
when b.fid  IS NULL then -1 else b.fid end  as farea,
a.CONTENT AS FCONTENT,A.UPDATETIME AS FTIME,NULL AS FHREF,A.DELETED AS  FISDEL

 FROM Z_bidding A LEFT JOIN CCIC_AREA B ON charindex(b.fname,a.areaid)>0

和

SELECT  A.GCMC AS FNAME,A.JSDW AS FOWNER,case  b.fid
when  NULL then -1 else b.fid end  as farea,
a.CONTENT AS FCONTENT,A.UPDATETIME AS FTIME,NULL AS FHREF,A.DELETED AS  FISDEL

 FROM Z_bidding A LEFT JOIN CCIC_AREA B ON charindex(b.fname,a.areaid)>0

执行的结果是不一样的

A. 使用带有简单  CASE  函数的  SELECT  语句

USE  AdventureWorks;
GO
SELECT    ProductNumber, Category  =
       CASE  ProductLine
          WHEN   ' R '   THEN   ' Road '
          WHEN   ' M '   THEN   ' Mountain '
          WHEN   ' T '   THEN   ' Touring '
          WHEN   ' S '   THEN   ' Other sale items '
          ELSE   ' Not for sale '
       END ,
   Name
FROM  Production.Product
ORDER   BY  ProductNumber;
GO


B.使用带有简单  CASE  函数和  CASE  搜索函数的  SELECT  语句

USE  AdventureWorks;
GO
SELECT    ProductNumber, Name,  ' Price Range '   =  
       CASE  
          WHEN  ListPrice  =    0   THEN   ' Mfg item - not for resale '
          WHEN  ListPrice  <   50   THEN   ' Under $50 '
          WHEN  ListPrice  >=   50   and  ListPrice  <   250   THEN   ' Under $250 '
          WHEN  ListPrice  >=   250   and  ListPrice  <   1000   THEN   ' Under $1000 '
          ELSE   ' Over $1000 '
       END
FROM  Production.Product
ORDER   BY  ProductNumber ;
GO