题解 | #分别满足两个活动的人#

SELECT uid, 'activity1' AS activity
FROM examination_info JOIN exam_record USING (exam_id)
GROUP BY uid
HAVING MIN(score) >= 85
UNION ALL
SELECT uid, 'activity2' AS activity
FROM examination_info JOIN exam_record USING (exam_id)
WHERE TIMESTAMPDIFF(SECOND,start_time,submit_time) <= (duration / 2 * 60)
  AND difficulty = 'hard'
GROUP BY uid
HAVING MIN(score) >= 80
ORDER BY uid