题解 | #统计复旦用户8月练题情况#

SELECT a.device_id, a.university, 
count(b.question_id) as question_cnt,
sum(case when b.result = "right" then 1 else 0 end) 
as right_question_cnt
FROM user_profile as a
left join 
question_practice_detail as b
on a.device_id = b.device_id
WHERE a.university = "复旦大学" AND (MONTH(b.date)=08 or b.date is null)
group by a.device_id;