select tag,sum(if_retweet) retweet_cut,round(sum(if_retweet)/count(*),3) retweet_rate from tb_user_video_log uvl,tb_video_info vi where uvl.video_id=vi.video_id and datediff(date((select max(start_time)from tb_user_video_log)),date(start_time))<=29 group by tag order by retweet_rate desc 感觉很奇怪的,怎...