select t.course_id, course_name, max(num) as max_num from( select a1.course_id, count(distinct a2.user_id) as num from attend_tb a1 join attend_tb a2 on a1.course_id = a2.course_id and a1.out_datetime > a2.in_datetime and a1.out_datetime <= a2.out_datetime group by 1, a1.user_id)t join course...