题解 | 统计复旦用户8月练题情况

使用left join方式，注意月份要在on条件下

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