题解 | #分别满足两个活动的人#

select uid,'activity1' as activity 
from exam_record where year(start_time)=2021 group by uid having avg(score) >=85
union all
select uid,'activity2' as activity  from exam_record t join examination_info t1 using(exam_id)
where difficulty = 'hard' and TIMESTAMPDIFF(second,start_time,submit_time) <= t1.duration*30
and score >80 and year(start_time)= 2021
order by uid 

这道题核心的点就是 时间差如何求的

TIMESTAMPDIFF(second/minute,starttime,endtime)

这道题不用使用分钟来求，会忽略道秒的细节，导致出错。