select   b.tag,   concat(     round(       avg(         case           when timestampdiff(second, start_time, end_time) ...

select     university,     difficult_level,     sum(date) / count(u.device_id) avg_answer_cnt   from     (       select         *       from        &n...

select     university,     difficult_level,     sum(date) / count(university)   from     user_profile a,     (       select         device_id,         coun...

select     university,     sum(date) / count(a.device_id)   from     user_profile a,     (       select         device_id,         COUNT(question_id) date   &nb...

select gender,  university,  COUNT(id) user_num,  avg(active_days_within_30) avg_active_day,  avg(question_cnt) avg_question_cnt from user_profile group by university, gender;