相关疑难解决方法(0)

我正在使用count并group by获得每天注册的订阅者数量:

  SELECT created_at, COUNT(email)  
    FROM subscriptions 
GROUP BY created at;

结果:

created_at  count
-----------------
04-04-2011  100
05-04-2011   50
06-04-2011   50
07-04-2011  300

我想每天获得累计订阅者总数.我怎么得到这个？

created_at  count
-----------------
04-04-2011  100
05-04-2011  150
06-04-2011  200
07-04-2011  500