题解 | #分别满足两个活动的人#

select distinct uid,
'activity2' as activity
from examination_info
join exam_record
using(exam_id)
# 内连接两个表
where year(start_time)='2021' and difficulty='hard' and score>80
and timestampdiff(minute,start_time,submit_time)<30 
# 选出第二种情况2021年完成困难题目，分数大于80，且用时小雨30分钟
union all
# 合并第二种情况
select distinct uid,
'activity1' as activity
from exam_record
group by uid
having min(score)>=85
# 每个相同uid分组下 纯在分数大于85的提交
order by uid,right(activity,1)
# 根据UID排序