明确题意:请你统计每个科目最大同时在线人数问题分解:计算在线人数变动情况:select course_id,in_datetime dt,1 uv from attend_tb union all select course_id,out_datetime dt,-1 uv from attend_tb关联课程表和上课情况表:join course_tb ct on t1.course_id = ct.course_id计算同时在线人数:sum(uv) over(partition by course_id order by dt,uv desc)按科目分组:group by course_i...