题解 | #统计复旦用户8月练题情况#

sum(if(qpd.result = 'right', 1, 0) as right_question_cnt)

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