题解 | 每类视频近一个月的转发量/率

select 
    tag,
    sum(if_retweet) retweet_cnt,
    round(sum(if_retweet)/count(tu.video_id),3) retweet_rate
from tb_user_video_log tu 
join tb_video_info tv
  on tu.video_id = tv.video_id
where datediff((select max(start_time) from tb_user_video_log ),tu.start_time) < 30
group by tag
order by retweet_rate desc