题解 | #分别满足两个活动的人#

SELECT * from (SELECT uid,'activity2' activity from (
SELECT er.*,ei.tag,ei.difficulty,ei.duration,TIMESTAMPDIFF(second,start_time,submit_time) subtime FROM `exam_record` er join examination_info ei on er.exam_id=ei.exam_id
where score >80 and ei.difficulty='hard'
)t1 
where subtime<=duration*60/2  
union 
SELECT distinct uid,'activity1' activity from exam_record where score>=85 GROUP BY uid HAVING MIN(score)>=85
)t2
ORDER BY uid,activity;

#正确做法：按照分组最小值>80筛选出每一次答题都大于80分的uid
SELECT distinct uid,'activity1' activity from exam_record where score>=85 GROUP BY uid HAVING MIN(score)>=85