题解 | #牛客直播各科目出勤率#

select b.course_id,course_name,
    round(count(distinct(case when timestampdiff(minute,in_datetime,out_datetime)>=10 then b.user_id else null end ))*100/count(distinct (case when if_sign = 1 then b.user_id else null end)),2)  as attend_rate
from course_tb c 
right join behavior_tb b
on c.course_id=b.course_id
left join attend_tb a 
on b.user_id=a.user_id and b.course_id=a.course_id
group by b.course_id,course_name
order by b.course_id