题解 | #每类视频近一个月的转发量/率#

1 本题的思路难点就是slq怎么处理近三十天，关于时间函数的熟悉程度
date_sub(,) 
datediff()

整体答案如下：

select 
b.tag,
sum(if_retweet),
cast(sum(a.if_retweet) / count(a.uid) as decimal(10,3)) as retweet_rate
from tb_user_video_log a
left join tb_video_info b
on a.video_id=b.video_id
where date_sub(date((select max(start_time) from tb_user_video_log)) , interval 30 day)  < date(a.start_time)
group by b.tag
order by retweet_rate desc