题解 | #分别满足两个活动的人#

select *
from
#每次试卷得分都能到85分的人
(select uid,'activity1'
from exam_record
where year(submit_time)=2021 
group by uid
having sum(score)/count(uid)>=85
union all
#至少有一次用了一半时间就完成高难度试卷且分数大于80的人
select distinct uid,'activity2'
from exam_record
     join examination_info using(exam_id)
where difficulty='hard' and year(submit_time)=2021 and timestampdiff(SECOND,start_time,submit_time)<=duration*30 and score > 80 ) data1
order by uid