题解 | 最受欢迎的top3课程

select p.cid,
count(*) pv,
round(sum(timestampdiff(minute,start_time,end_time)),3) time_len
from course_info_tb c right join play_record_tb p on c.cid=p.cid
#where timestampdiff(day,date(start_time),release_date)<=7
where datediff(start_time,release_date)<=7
group by cid
having avg(score)>=3
order by pv desc,time_len desc
limit 3

注意第5行和第6行的区别

要改正的话，应该是where timestampdiff(day,date(start_time),release_date)>=-7

或者where timestampdiff(day,release_date，date(start_time))<=7