题解 | #统计复旦用户8月练题情况#

SELECT
    u.device_id,
    u.university,
    count(q.question_id) as question_cnt,
    sum(
        case
            when q.result = 'right' then 1
            else 0
        end
    ) as right_question_cnt
FROM
    user_profile as u
    left JOIN question_practice_detail as q on u.device_id = q.device_id
    and month (q.date) = 8
where
    u.university = '复旦大学'
group by
    u.device_id,
    u.university

原来还有sum case这个操作，

不要漏写了university里的s