select a.university, c.difficult_level, round( count(b.question_id) / count(distinct b.device_id), 4 ) as avgNum from user_profile a, question_practice_detail b, question_detail c where a.device_id = b.device_id and b.question_id = c.question_id and a.university = '山东大学' group by a.university, c.dif...