题解 | #分别满足两个活动的人#

select uid
     , 'activity1' activity
from exam_record er
         inner join examination_info ei on er.exam_id = ei.exam_id
where year(er.submit_time) = 2021
  and score >= 85
group by uid
union all
select uid
     , 'activity2' activity
from exam_record er
         inner join examination_info ei on er.exam_id = ei.exam_id
where year(er.submit_time) = 2021
  and timestampdiff(minute, start_time, submit_time) < ei.duration / 2
  and score > 80
  and ei.difficulty = 'hard'
group by uid
order by uid;