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
http://www.nowcoder.com/practice/bdd30e83d47043c99def6d9671bb6dbf
select x.course_id, course_name,count(distinct user_id) from attend_tb x join course_tb y using(course_id) where time(in_datetime)<='19:00:00' and time(out_datetime)>='19:00:00' group by 1,2 order by 1
