题解 | #牛客每个人最近的登录日期(四)#

select date,
sum(case when (user_id,date) in (select user_id,min(date) from login group by user_id) then 1 else 0 end) as new
from login
group by date
order by date

按照日期分类，case when的使用，去选择用户ID和最新登陆日期