题解 | 最受欢迎的top3课程

with t1 as(select
uid,
a.cid cid,
timestampdiff(minute,start_time,end_time) time_len,
score
from
course_info_tb a inner join play_record_tb b on a.cid=b.cid
where start_time < date_add(release_date,interval 7 day))

select
cid,
count(*) pv,
sum(time_len) time_len
from
t1
group by cid
having avg(score)>=3
limit 3