题解 | #筛选限定昵称成就值活跃日期的用户#

select
    ui.uid,
    nick_name,
    achievement
from
    user_info ui
    left join exam_record er on ui.uid = er.uid
    left join practice_record pr on ui.uid = pr.uid
where
    nick_name like '牛客%号'
    and achievement between 1200 and 2500
group by ui.uid
having
    (max(pr.submit_time) is not null and max(er.start_time) is not null and date_format(if(max(pr.submit_time)<=max(er.start_time),max(er.start_time),max(pr.submit_time)),'%Y%m')='202109')
    or
    (max(pr.submit_time) is not null and max(er.start_time) is null and date_format(max(pr.submit_time),'%Y%m')='202109')
    or
    (max(pr.submit_time) is  null and max(er.start_time) is not null and date_format(max(er.start_time),'%Y%m')='202109')

踩坑了，max(null)返回none，max(null)<=max(1)也返回none