如何写统计用户登录系统时间的sql?

我现在的数据是这样的，userid表示用户登录系统的代码，time表示登录登出系统的时间，status，1表示登录，2表示登出；
userid time status
user001 2011-06-10 14:57:24.000 1
user001 2011-06-10 15:03:41.000 2
user001 2011-06-10 16:50:00.000 1
user001 2011-06-10 17:03:40.000 2
user001 2011-06-10 17:20:40.000 1
user002 2011-06-10 10:01:20.000 1
user002 2011-06-10 10:20:24.000 1
user002 2011-06-10 10:40:40.000 2
user002 2011-06-10 13:50:00.000 1
user002 2011-06-10 15:03:40.000 2 
我想要的结果是：
用户代码 登录时间区间  
user001 2011-06-10 14:57:24.000--2011-06-10 15:03:41.000 6 minutes  
user001 2011-06-10 16:50:00.000--2011-06-10 17:03:40.000 13 minutes
user001 2011-06-10 17:20:40.000 0 minutes
user002 2011-06-10 10:01:20.000--2011-06-10 10:40:40.000 39 minutes  
user002 2011-06-10 10:20:24.000-- 0 minutes
user002 2011-06-10 13:50:00.000--2011-06-10 15:03:40.000 73minutes  

我的目的是统计每个用户登录系统的时间的汇总。

SQL code

select a.userid,a.time,b.time,datediff(mi,,a.time,b.time)
from tb a left join ,tb b 
on a.userid=b.userid and b.status=2
and b.time=(select top 1 time from tb c 
            where c.userid=a.userid and c.status=2
            and c.time>a.time order by c.time)
where a.status=1 

SQL code

declare @t table(iId int identity(1,1),[userid] varchar(20), [time] datetime, [status] int)
Insert @t([userid], [time], [status])
select 'user001', '2011-06-10 14:57:24.000', 1 Union All
select 'user001', '2011-06-10 15:03:41.000', 2 Union All
select 'user001', '2011-06-10 16:50:00.000', 1 Union All
select 'user001', '2011-06-10 17:03:40.000', 2 Union All
select 'user001', '2011-06-10 17:20:40.000', 1 Union All
select 'user002', '2011-06-10 10:01:20.000', 1 Union All
select 'user002', '2011-06-10 10:20:24.000', 1 Union All
select 'user002', '2011-06-10 10:40:40.000', 2 Union All
select 'user002', '2011-06-10 13:50:00.000', 1 Union All
select 'user002', '2011-06-10 15:03:40.000', 2  


select *, ISNULL(DATEDIFF(MINUTE, [time], EndDate), 0) iMINUTE from (
select *, (select top 1 [time] from @t where A.userid=userid and [status] = 2 and A.iId<=iId order by iId) EndDate from @t A where [status] = 1
) A


iId         userid               time                    status      EndDate                 iMINUTE
----------- -------------------- ----------------------- ----------- ----------------------- -----------
1           user001              2011-06-10 14:57:24.000 1           2011-06-10 15:03:41.000 6
3           user001              2011-06-10 16:50:00.000 1           2011-06-10 17:03:40.000 13
5           user001              2011-06-10 17:20:40.000 1           NULL                    0
6           user002              2011-06-10 10:01:20.000 1           2011-06-10 10:40:40.000 39
7           user002              2011-06-10 10:20:24.000 1           2011-06-10 10:40:40.000 20
9           user002              2011-06-10 13:50:00.000 1           2011-06-10 15:03:40.000 73

(6 行受影响)

这个有那么点漏洞，就是有进无出的不能判断出来