题解 | #统计复旦用户8月练题情况#

select u.device_id,university,sum(case when result is not null then 1 else 0 end),
sum(case result when 'right' then 1 else 0 end)
from user_profile u
left join question_practice_detail q
on u.device_id=q.device_id
where university='复旦大学'
and (MONTH(date)=8 or date is null)
group by u.device_id