题解 | #统计复旦用户8月练题情况#

select u.device_id, u.university, COUNT(qpd.question_id) question_cnt, count( case when qpd.result = 'right' then 1 else null end) right_questoin_cnt FROM user_profile as u left JOIN question_practice_detail as qpd on u.device_id = qpd.device_id where u.university = '复旦大学' and (month(qpd.date) = 08 or month(qpd.date) is null) group by u.device_id

整体思路就是直接干 不知道为什么后面一定要补一个month(qpd.date) is null 才能筛选出来 为0 的答案