题解 | #牛客每个人最近的登录日期(四)#

方法一：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;
方法二:
from直接带着表查询记得指定select a.date from （select...） as a，不然会报错【Every derived table must have its own alias】 ;
rank在mysql中是关键字，不能直接命名，改为t_rank；
： select a.date , sum( case when t_rank =1 then 1 else 0 end) from (select date,
row_number()  over(partition by user_id order by date) as t_rank from login ) as a group by date order by date;