题解 | #牛客直播开始时各直播间在线人数#
牛客直播开始时各直播间在线人数
https://www.nowcoder.com/practice/bdd30e83d47043c99def6d9671bb6dbf
select course_id, course_name, sum(case when time(in_datetime)<'19:00:00' and time(out_datetime)>'19:00:59' then 1 when time(in_datetime) between '19:00:00' and '19:00:59' then 1 else 0 end) as online_num from course_tb join attend_tb using(course_id) group by course_id,course_name order by course_id