要求很少，只需要判断用户的序号是否是第一个，用排名函数就可以
牛客每个人最近的登录日期(四)
https://www.nowcoder.com/practice/e524dc7450234395aa21c75303a42b0a
select date,sum(case when rk = 1 then 1 else 0 end)
from
(
select
date,
row_number() over (partition by user_id) as rk
from
login
) as t1
group by date
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