题解 | #每类视频近一个月的转发量/率#

select b.tag as tag,sum(a.if_retweet) as retweet_cut,round(sum(a.if_retweet)/count(a.video_id),3) as retweet_rate
from tb_video_info b right join tb_user_video_log a using(video_id)
##限定时间为此题难点，话说题目表述很让人迷惑
where timestampdiff(day,start_time,(select max(start_time) from tb_user_video_log))<30
group by b.tag
order by retweet_rate desc