2008-03-23 10:10:15.000
2008-03-23 10:12:17.000
2008-03-23 10:12:33.000
2008-03-23 10:13:37.000
2008-03-23 10:42:39.000
2008-03-23 10:42:41.000
2008-03-23 10:43:42.000
2008-03-23 10:44:38.000
2008-03-23 11:00:05.000
2008-03-23 11:01:19.000
2008-03-23 11:01:36.000
2008-03-23 11:02:11.000
2008-03-23 11:23:22.000
2008-03-23 11:45:06.000
要求：
以上时间段是一个例子，我的要求是，整个数据库按时间字段排序，然后判断出时间间隔大于20分钟的时间段，
例如：
2008-03-23 10:13:37.000     
2008-03-23 10:42:39.000   

2008-03-23 11:02:11.000
2008-03-23 11:23:22.000
2008-03-23 11:45:06.000

DATEDIFF(minute,LastVisitTime,getdate())>20这个函数虽然符合一点要求，但是不行，他取得是当前时间，
我要判断的是上一条记录和下一条记录的时间间隔大于20分钟的！

请帮忙看下！谢谢！

create table tb(时间 datetime)
insert into tb values('2008-03-23 10:10:15.000')
insert into tb values('2008-03-23 10:12:17.000')
insert into tb values('2008-03-23 10:12:33.000')
insert into tb values('2008-03-23 10:13:37.000')
insert into tb values('2008-03-23 10:42:39.000')
insert into tb values('2008-03-23 10:42:41.000')
insert into tb values('2008-03-23 10:43:42.000')
insert into tb values('2008-03-23 10:44:38.000')
insert into tb values('2008-03-23 11:00:05.000')
insert into tb values('2008-03-23 11:01:19.000')
insert into tb values('2008-03-23 11:01:36.000')
insert into tb values('2008-03-23 11:02:11.000')
insert into tb values('2008-03-23 11:23:22.000')
insert into tb values('2008-03-23 11:45:06.000')
go

select m.时间 开始时间 , n.时间 结束时间 from
(select 时间 , px = (select count(*) from tb where 时间 < t.时间) + 1 from tb t) m,
(select 时间 , px = (select count(*) from tb where 时间 < t.时间) + 1 from tb t) n
where m.px = n.px - 1 and datediff(mi , m.时间 , n.时间) > 20

这个语句虽然可以达到我得要求！但是还有一点问题！

create table tb(时间 datetime，编号)
insert into tb values('2008-03-23 10:10:15.000',1)  
insert into tb values('2008-03-23 10:12:17.000',1)  
insert into tb values('2008-03-23 10:12:33.000',1)  
insert into tb values('2008-03-23 10:13:37.000',1)  
insert into tb values('2008-03-23 10:42:39.000',1)  
insert into tb values('2008-03-23 10:42:41.000',1)  
insert into tb values('2008-03-23 10:43:42.000',1)  
insert into tb values('2008-03-23 10:44:38.000',1)  
insert into tb values('2008-03-23 11:00:05.000',1)  
insert into tb values('2008-03-23 11:01:19.000',2)  
insert into tb values('2008-03-23 11:01:36.000',2)  
insert into tb values('2008-03-23 11:02:11.000',2)  
insert into tb values('2008-03-23 11:23:22.000',2)  
insert into tb values('2008-03-23 11:45:06.000',2)  

我想先查出编号为“1”的所有数据，然后按照这个再行筛选！
谢谢！