题解 | 统计每个学校的答过题的用户的平均答题数

# select u.university,
# round(count(q.question_id)/count(distinct(q.device_id)),4) as avg_answer_cnt
# from user_profile as u, question_practice_detail as q
# where u.device_id = q.device_id
# group by u.university;


select university,
round(count(q.question_id)/count(distinct(q.device_id)),4) as avg_answer_cnt
from user_profile u join question_practice_detail q on u.device_id = q.device_id
group by u.university;