OrderBy子句无效

Question

这是我的查询导致上述错误。我觉得这是顺序之一，但是哪一个？

select cast(max(DateAndTime) - min(DateAndTime) as time) as DownTime
from (select pt.*,
         sum(case when datediff(second, prevdt, DateAndTime) <= 1 then 0 else 1 end) over 
             (order by DateAndTime) as grp
  from (select pt.*, lag(DateAndTime) over (order by DateAndTime) as prevdt
        from IncomingProductTracker pt
        where Line1AFaultStatus = 1 and
              DateAndTime > '2014-04-07 8:00:00' and
              DateAndTime < '2014-04-07 17:00:00'
       ) pt
 ) pt
group by grp
order by 1;