题解 | 每天登陆最早的用户的内容喜好

SELECT 
    e.log_day,
    u.user_id,
    u.hobby
FROM 
(SELECT 
        DATE(log_time) AS log_day,
        MIN(log_time) AS earliest_time
    FROM 
        login_tb
    GROUP BY 
        DATE(log_time)
) e
JOIN 
    login_tb l ON l.log_time = e.earliest_time
JOIN
    user_action_tb u ON u.user_id = l.user_id
ORDER BY 
    e.log_day;

子查询 --先按天找最早登录时间

主查询-再按时间找用户