select uid,'activity1' as activity
from examination_info ei
join exam_record er on ei.exam_id=er.exam_id
where score >= 85
and year(start_time)=2021

union 

select distinct uid,'activity2' as activity
from examination_info ei
join exam_record er on ei.exam_id=er.exam_id
where difficulty ='hard'
and score>80
and timestampdiff(second,start_time,submit_time)/60<=0.5*duration
and year(start_time)=2021

order by uid

分别求a1 和a2，然后union 起来