题解 | #筛选限定昵称成就值活跃日期的用户#

select uid,nick_name,achievement
from user_info
where nick_name like "牛客%号" and achievement between 1200 and 2500
and uid in (
        select uid
        from (
            select uid, start_time as 'act_time'        from exam_record
            union all
            select uid, submit_time as 'act_time'       from practice_record
        ) as a
        group by uid
        having date_format(max(act_time), '%Y%m')='202109'
    )

这道题的重点是需要在练习和答题中找到最近一次活跃在九月的。