题解 | #牛客直播各科目出勤率#

分为两个表去求解该题目，分别求出出勤人数和报名人数

坑点：计算同一用户在同一个科目总的直播时长>10分钟

(select course_id,course_name,count(user_id) u1 from
(select user_id,course_id,course_name,sum(timestampdiff(minute,in_datetime,out_datetime)) sumtime
from attend_tb 
join course_tb  using(course_id)
group by user_id,course_id,course_name having sumtime>10)t0
group by course_id,course_name)t
join
(select course_id,course_name,sum(if_sign) s1 from course_tb
join behavior_tb using(course_id)
group by course_id,course_name)t1
using(course_id)
order by course_id