题解 | 分别满足两个活动的人

SELECT DISTINCT uid, 'activity1' AS activity
FROM exam_record
WHERE YEAR(submit_time) = 2021
AND score >= 85

UNION ALL 

SELECT DISTINCT er.uid, 'activity2' AS activity
FROM exam_record AS er 
LEFT OUTER JOIN examination_info AS ei
ON er.exam_id = ei.exam_id
WHERE YEAR(er.submit_time) = 2021
AND ei.difficulty = 'hard'
AND TIMESTAMPDIFF(minute, er.start_time, er.submit_time) < (ei.duration / 2)
AND er.score >= 80

ORDER BY uid;