sql server执行存储过程慢的问题

要实现一个根据时间查询数据生成报表的功能，写了如下存储过程：

CREATE   Procedure   [ dbo ] . [ Report_SearchEnginOnAccount ]
@FromDate   DATETIME ,
@ToDate   DATETIME

AS

SELECT   ''   as  ADGroup
      , ''   as  Content
      , ''   as  KeyWord
      , sum ( [ ViewAdPV ] )  as  ViewAdPV
      , sum ( [ Listing ] )  as  Listing
      , sum ( [ NB ] )  as  NB
      , sum ( [ NU ] )  as  NU
      , sum ( [ BouncedRate ] )  as  BouncedRate
      , sum ( [ BouncedUV ] )  as  BouncedUV
      , sum ( [ UV ] )  as  UV
      , sum ( [ PV ] )  as  PV
      , [ Date ]
      , sum ( [ ClickCount ] )  as  ClickCount 
      , sum ( [ ShowCount ] )  as  ShowCount
      , sum ( [ ClickRate ] )  as  ClickRate
      , sum ( [ TotalPrice ] )  as  TotalPrice
   FROM   [ SmallChannelDB ] . [ dbo ] . [ SearchEnginDataReport_View ]
   WHERE   [ Date ] <=   @ToDate   AND   [ DATE ] >= @FromDate  
   Group   by   [ date ]
GO

      在使用过程中出现了超时的错误，经查发现是因为存储过程执行时间太长，20万左右的数据一分多钟都没有执行完……我以为是sql语句里面出现的问题，然后直接把@ToDate和@FromDate赋值执行，不到1s就出结果了，后来经公司sql server高手指导，把View换成直接的表连接，然后给两个表的Date列分别加上索引，问题解决，但不知道具体原因是什么。结果第二天又恢复原状了……

     后来在网上搜索资料，发现在sql server中有一个叫“Parameter sniffing”的特性（

http://blog.csdn.net/emili/article/details/2192081），有几个解决办法，一个就是declare一个变量，然后给这个变量赋上参数的值，在存储过程中使用此变量的值就可以了。