题解 | #分别满足两个活动的人#

select uid,'activity1' activity from exam_record er
join examination_info ei
on er.exam_id=ei.exam_id
where uid not in (select uid from exam_record where score<85) and year(start_time)=2021
union
select uid,'activity2' activity from exam_record er
join examination_info ei
on er.exam_id=ei.exam_id
where timestampdiff(second,start_time,submit_time)<=duration*30 and score>80 and difficulty='hard'
and year(start_time)=2021
order by uid;

成绩全部大于等于85，只要uid不在有一个成绩小于85的组中就行

timestampdiff(unit,begin,end)，返回end-begin的结果，单位为unit(如second，minute等)