7天内活跃用户统计如何写

7天内活跃用户统计怎么写
7天内访问2次以上的用户，就算活跃用户，该怎么统计。

比方说
        ID         用户        TIME                         活跃用户
                1             aa                    2014.1.1
                 2           bb                     2014.1.1                    0
               3              aa                   2014.1.2                       
                4              bb                 2014.1.2 
               5               cc                   2014.1.2                      2
                6             aa                   2014.1.3
               7               cc                  2014.1.3                         2
               8               aa                  2014.1.4                          1
               9               aa                  2014.1.7
               10              cc                 2014.1.7
                11             dd                2014.1.7                         2
                12             
类似这样的统计数

       
------解决方案--------------------
7天是以哪一天为周期的其实，换成每周OK？
------解决方案--------------------
select username,次数
from
(
select username,COUNT(1) as 次数
from test
where DATEDIFF(day,time1,GETDATE())<=7
group by username
) as temp
where temp.次数>=2