题解 | 每天登陆最早的用户的内容喜好

select 
log_day, user_id, hobby
from (
    select 
    date(l.log_time) as log_day, l.log_time, l.user_id, u.hobby,
    row_number() over(partition by date(l.log_time) order by l.log_time asc) as rk
    from login_tb as l
    left join user_action_tb as u
    on l.user_id=u.user_id
) as r1

where rk=1

1. 联合查询全数据
2. 利用窗口函数对日子进行排名
3. 提取子查询，过滤第一名数据