with t1 as ( select user_id,course_id,in_datetime dt ,1 as uv from attend_tb union select user_id,course_id,out_datetime dt,-1 as uv from attend_tb ), t2 as ( select * ,sum(uv) over(partition by course_id order by dt ) num from t1 ), t3 as( select course_id,max(num) max_num from t2 group by course_i...