INSERT INTO exam_record(uid, exam_id, start_time, submit_time, score)

VALUES (1001,9001,'2021-09-01 22:11:12','2021-09-01 23:01:12',90),

(1002,9002,'2021-09-04 07:01:02',null,null);

INSERT INTO exam_record

VALUES (null,1001,9001,'2021-09-01 22:11:12','2021-09-01 22:11:12' + INTERVAL 50 minute,90),

(null,1002,9002,'2021-09-04 07:01:02',null,null);

INSERT INTO exam_record_before_2021(uid,exam_id,start_time,submit_time,score) -- VALUE用于填具体值，无具体值不用加

SELECT uid,exam_id,start_time,submit_time,score FROM exam_record

WHERE submit_time < '2021-01-01 00:00:00'

REPLACE INTO examination_info

VALUES(null,9003,'SQL','hard',90,'2021-01-01 00:00:00');

UPDATE examination_info SET tag='Python' WHERE tag='PYTHON'

UPDATE exam_record

SET submit_time='2099-01-01 00:00:00', score=0

WHERE submit_time IS NULL AND start_time<'2021-09-01 00:00:00'

DELETE FROM exam_record

WHERE timestampdiff(minute,start_time,submit_time)<5 AND score<60

DELETE FROM exam_record

WHERE submit_time IS NULL OR TIMESTAMPDIFF(minute,start_time,submit_time)<5

ORDER BY start_time LIMIT 3

TRUNCATE exam_record