题解 | #分别满足两个活动的人#

select
    *
from
    (
        select
            uid,
            'activity1' as activity
        from
            exam_record
        where
            score >= 85
        group by
            uid
        union
        select
            uid,
            'activity2' as activity
        from
            examination_info
            join exam_record using (exam_id)
        where
            TIMESTAMPDIFF (second, start_time, submit_time) < duration * 0.5 * 60
            AND score >= 80
            AND difficulty = 'HARD'
    ) as newform
order by
    uid asc,
    activity asc

本题基本没有难度，就是通过2个子查询将符合条件的uid查找出来，并带上'activity'的标识，并在总循环进行一个排序，因为子循环无法做排序