select a.id,a.time as Intime, b.Time as OutTime, 
    datediff(ss/*以秒记*/,a.time,b.time) as LT 
from tb a cross apply 
  (select top (1)* from tb b where a.ID = b.ID and b.time > a.time 
     and b.device = 2 order by b.time desc)p 
where a.device = 1

------解决方案--------------------
SQL code
WITH test (id,TIME,device)
 AS 
 (
 SELECT 1,'2012-09-23 12:10:01',1
 UNION ALL 
 SELECT 1,'2012-09-24 12:10:01',2 --模拟跨天
 UNION ALL 
 SELECT 2,'2012-09-23 12:10:01',1
 UNION ALL 
 SELECT 2,'2012-09-23 14:10:01',2 --模拟当天
 )
 --SELECT * FROM test 
 
 SELECT id,InTime=MAX(CASE WHEN device=1 THEN TIME END ),OutTime=MAX(CASE WHEN device=2 THEN TIME END ),
 CASE WHEN DATEPART(DAY,MAX(CASE WHEN device=1 THEN TIME END ))=DATEPART(DAY,MAX(CASE WHEN device=2 THEN TIME END )) 
 THEN CONVERT(VARCHAR(10),DATEDIFF (hh,MAX(CASE WHEN device=1 THEN TIME END ),MAX(CASE WHEN device=2 THEN TIME END)))+'小时'
 + CONVERT(VARCHAR(10),DATEDIFF (mi,DATEPART(mi,MAX(CASE WHEN device=1 THEN TIME END )),DATEPART(mi,MAX(CASE WHEN device=2 THEN TIME END))))
 +'分'+CONVERT(VARCHAR(10),DATEDIFF (ss,DATEPART(ss,MAX(CASE WHEN device=1 THEN TIME END )),DATEPART(ss,MAX(CASE WHEN device=2 THEN TIME END))))+'秒' 
 
 ELSE  CONVERT(VARCHAR(10),DATEDIFF (hh,MAX(CASE WHEN device=1 THEN TIME END ),MAX(CASE WHEN device=2 THEN TIME END)))+'小时'
 + CONVERT(VARCHAR(10),DATEDIFF (mi,DATEPART(mi,MAX(CASE WHEN device=1 THEN TIME END )),DATEPART(mi,MAX(CASE WHEN device=2 THEN TIME END))))
 +'分'+CONVERT(VARCHAR(10),DATEDIFF (ss,DATEPART(ss,MAX(CASE WHEN device=1 THEN TIME END )),DATEPART(ss,MAX(CASE WHEN device=2 THEN TIME END))))+'秒'
 END 
 FROM test 
 GROUP BY id
 
 /*
 ----------- ------------------- ------------------- --------------------------------------
 1           2012-09-23 12:10:01 2012-09-24 12:10:01 24小时0分0秒
 2           2012-09-23 12:10:01 2012-09-23 14:10:01 2小时0分0秒
 警告: 聚合或其他 SET 操作消除了 Null 值。
 
 (2 行受影响)
 */

------解决方案--------------------
SQL code

select #a.id ,b.Intime,b.OutTime,
datediff(s,b.OutTime,b.Intime) as LT 
from #a cross join(
select case when device=1 then max(time) end as Intime,
case when device=2 then min(time) end as  OutTime from #a group by device) as b