题解 | 最受欢迎的top3课程

关键：计算日期差的函数TIMESTAMPDIFF(minute,start_time,end_time)，datediff(start_time,release_date)。明确两层筛选：1、一周内；2、平均评分大于3

select p.cid cid
,count(p.id) pv
,sum(TIMESTAMPDIFF(minute,start_time,end_time)) time_len
from play_record_tb p
left join course_info_tb c on p.cid=c.cid
where datediff(start_time,release_date) <7
group by p.cid
having avg(score)>=3
order by count(p.id) desc,sum(TIMESTAMPDIFF(minute,start_time,end_time)) desc
limit 3