题解 | #牛客每个人最近的登录日期(四)#

之前没有加user_id结果错误，运行没有问题，觉得case when语句没有用到user_id就省略了，这个因为Mysql还是比较松，正确的做法是group by 后面的列，select后面要有该列
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
    )
from login
group by date
order by date;