写完这段突然感觉自己很牛，，蜜汁自信了，结果下一题又不会做。。

with 
	new_user 
as (  
  select 
  	user_id, date, row_number() over (partition by user_id order by date) as rn 
  from 
  	login
  order by 
  	user_id
)

select 
	date, ifnull(count(distinct case when rn = 1 then user_id else null end),0) as new 
from 
	new_user
group by 
	date