select login.date,ifnull(n1.new_num,0)
from login left join
(select a.t_date,count(user_id) as new_num
from
(select min(date) as t_date,user_id from login group by user_id) as a
group by t_date) as n1
on login.date=n1.t_date
group by login.date order by login.date

这道题其实最开始自己没想出来有点可惜 因为已经只差一个表格的合并了 教训就是如果当我们这边需要一列的全部信息时 就去找那个表有 然后合并就好了
ifnull的使用：https://www.yiibai.com/mysql/ifnull.html