学步园

第一种写法:
语句执行花费时间(毫秒)  330

 SELECT  
      VGoodsLocationC,
      Vtrancode,
      VStartPoint,
      V_OldGBGrade,
      V_GBGrade,
      SUM(IPackageCount) AS IPackageCount,
      SUM(NWeight) AS NWeight    
      INTO ##storInTemp                 
  FROM 
      V_InStorehouseInfo 
  WHERE VGoodsLocationC 
        IN (SELECT VGoodsLocationC FROM V_InStorehouseInfo) 
    or VGoodsLocationC in (SELECT VGoodsLocationC_In FROM V_StorMoveInfo)
  GROUP BY  
      VGoodsLocationC,Vtrancode,VStartPoint,V_OldGBGrade,V_GBGrade     

第二种写法:
语句执行花费时间(毫秒)  563

SELECT                           
                VGoodsLocationC,
                Vtrancode,
                VStartPoint,
                V_OldGBGrade,
                V_GBGrade,
                SUM(IPackageCount) AS IPackageCount,
                SUM(NWeight) AS NWeight
                INTO  ##storInTemp 
                    FROM (
                        SELECT                           
                            VGoodsLocationC,
                            Vtrancode,
                            VStartPoint,
                            V_OldGBGrade,
                            V_GBGrade,
                            IPackageCount,
                            NWeight 
                 FROM V_InStorehouseInfo 
                 WHERE VGoodsLocationC 
                    IN (SELECT VGoodsLocationC FROM V_InStorehouseInfo) 
                    UNION ALL
                SELECT                           
                    VGoodsLocationC,
                    Vtrancode,
                    VStartPoint,
                    V_OldGBGrade,
                    V_GBGrade,
                    IPackageCount,
                    NWeight 
                    FROM V_InStorehouseInfo 
                    WHERE VGoodsLocationC 
                    IN (SELECT VGoodsLocationC_In FROM V_StorMoveInfo)
                    ) A
                      GROUP BY  
                         VGoodsLocationC,Vtrancode,VStartPoint,V_OldGBGrade,V_GBGrade

Why?