每个日期新登录的用户 如下就是抓出最小的那个日期
select user_id,min(date) date
from login
group by user_id

然后呢 再按照date的group by 和count 就可以得到 个数
可是 答案只对了一半 因为没登录的用户数据是0
所还得抓出Login的Date 进行左连接 然后 用ifnull 设为0

select a.date,ifnull(count(b.user_id),0) as new
from
(
select distinct date from login
) a
left join (
select user_id,min(date) date
from login
group by user_id
) b
on a.date=b.date
group by a.date
order by a.date