题解 | #牛客直播各科目出勤率#

select 
t3.course_id as course_id
,m.course_name as course_name
,round(t3.attend_rate*100,2) as attend_rate
from(select 
t1.course_id,t2.nnt/t1.amt as attend_rate
from 
(select 
course_id
,sum(if_sign) as amt
from behavior_tb
group by course_id) t1
left join 
(select 
course_id
,count(distinct user_id) as nnt
from attend_tb
where timestampdiff(minute,in_datetime,out_datetime)>=10
group by course_id 
)t2
on t1.course_id=t2.course_id) as t3
left join course_tb m
on t3.course_id=m.course_id
group by t3.course_id,m.course_name;

这个分数没办法一起写出来的话，就分子分母分开写