INSERT INTO exam_record_before_2021
SELECT NULL,uid, exam_id, start_time, submit_time, score
FROM exam_record
WHERE submit_time < '2021-01-01 00:00:00';
insert into exam_record_before_2021 select null,uid,exam_id,start_time,submit_time,score from exam_record where submit_time < '2021-01-01 00:00:00'