题解 | 每类视频近一个月的转发量/率

select 
  tag,
  sum(if_retweet) as cnt,
  round(avg(if_retweet),3) as retweet_rate
from 
  tb_user_video_log as t1
join 
  tb_video_info as t2
on 
  t1.video_id=t2.video_id
where
  t1.start_time>=date_add((select max(start_time) from tb_user_video_log),interval -30 day)
group by 
  tag
order by 
  retweet_rate desc;