题解 | #每类视频近一个月的转发量/率#

SELECT 
    info.tag,
    SUM(if_retweet) AS retweet_cut,
    ROUND(SUM(if_retweet) / COUNT(start_time), 3) AS retweet_rate
FROM tb_user_video_log lo
LEFT JOIN tb_video_info info ON lo.video_id = info.video_id
WHERE TIMESTAMPDIFF(DAY, start_time, 
(
    SELECT max(start_time)
    FROM tb_user_video_log
)
)<= 29
GROUP BY tag
ORDER BY retweet_rate DESC;