1.有用户互动的最近一个月的互动数据

2.每类视频的转发量和转发率（保留3位小数）

3.转发率降序排序

select
tag,
sum(if_retweet) retweet_cut,
round(sum(if_retweet) / count(*),3)  retweet_rate
from tb_user_video_log a
left join tb_video_info b
on a.video_id=b.video_id
where datediff(date((select max(start_time)from tb_user_video_log)),date(start_time))<=29
group by tag
order by retweet_rate desc