题解 | #分别满足两个活动的人#

(select distinct uid,'activity1' as activity from exam_record where score>=85)
union all
(select distinct uid,'activity2' as activity from exam_record join examination_info on examination_info.exam_id=exam_record.exam_id where score>80 and examination_info.difficulty='hard' and timestampdiff(minute,exam_record.start_time,exam_record.submit_time)<30)
order by uid