题解 | 统计复旦用户8月练题情况

select 
    up.device_id,
    university,
    count(qpd.question_id) as question_cnt,
    sum(
        case when qpd.result = 'right' then 1
            else 0
        end) as right_question_cnt
from user_profile up
left join question_practice_detail qpd on up.device_id = qpd.device_id and month(qpd.date) = 8
where university = '复旦大学'
group by up.device_id, up.university
order by up.device_id
  

要记得用left join要不然为某个复旦大学用户在 8 月没有练习记录0的值不会显示；