奇怪的SQLserver执行

 今天工作遇到，下面这段执行超慢，几乎不出来，在旧服务器上运行是可以的，一样代码，很快，在新虚拟服务器上，超慢。

　　　　　select * from 
        (
            select RowNum=row_number() over(order by AutoId desc),StartTime,cast(testtime/1000.00 as decimal(10,2)) as testtime,AutoId
            from dbo.FTMaster M
             WITH(NOLock) Where StartTime >='2014-01-01 00:00:00.000' and StartTime <'2014-12-31 23:00:00.000' and ModelIc='XXX' and Result=0 and TestType=3            
            and exists
            (    
                select AutoId from 
                (
                    select Min(BB.autoid) AutoID 
　　　　　　　　　　　　from 
                     (Select Max(StartTime) as starttime,SN From dbo.FTMaster WITH(NOLock) 
　　　　　　　　　　　　 Where StartTime >='2014-01-01 00:00:00.000' and StartTime <'2014-12-31 23:00:00.000' and ModelIc='XXX' and TestType=3 group by Sn) as AA 
                     inner join 
　　　　　　　　　　　　(Select AutoID,SN,StartTime From dbo.FTMaster WITH(NOLock) 　　
　　　　　　　　　　　　 Where StartTime >='2014-01-01 00:00:00.000' and StartTime <'2014-12-31 23:00:00.000' and ModelIc='XXX' and TestType=3 ) As BB 
　　　　　　　　　　　　 on AA.SN=BB.SN And AA.StartTime=BB.StartTime 
                    group by BB.SN
                ) t where t.AutoId=M.AutoId 
            )                
        ) 
        as MasterTable 
        WHERE RowNum between (1 - 1) * 12430 + 1 and 1 * 12430

执行里面的又很快， 为什么呢。

　　　　　　　select RowNum=row_number() over(order by AutoId desc),StartTime,cast(testtime/1000.00 as decimal(10,2)) as testtime,AutoId
            from dbo.FTMaster M
             WITH(NOLock) Where StartTime >='2014-01-01 00:00:00.000' and StartTime <'2014-12-31 23:00:00.000' and ModelIc='XXX' and Result=0 and TestType=3            
            and exists
            (    
                select AutoId from 
                (
                    select Min(BB.autoid) AutoID 
　　　　　　　　　　　　from 
                     (Select Max(StartTime) as starttime,SN From dbo.FTMaster WITH(NOLock) 
　　　　　　　　　　　　 Where StartTime >='2014-01-01 00:00:00.000' and StartTime <'2014-12-31 23:00:00.000' and ModelIc='XXX' and TestType=3 group by Sn) as AA 
                     inner join 
　　　　　　　　　　　　(Select AutoID,SN,StartTime From dbo.FTMaster WITH(NOLock) 　　
　　　　　　　　　　　　 Where StartTime >='2014-01-01 00:00:00.000' and StartTime <'2014-12-31 23:00:00.000' and ModelIc='XXX' and TestType=3 ) As BB 
　　　　　　　　　　　　 on AA.SN=BB.SN And AA.StartTime=BB.StartTime 
                    group by BB.SN
                ) t where t.AutoId=M.AutoId 
            )