select device_id,university,        count(question_id) as question_cnt,              sum(if(result='right',1,0)) as right_question_cnt FROM (select a.device_id,university,question_id,result,date from user_profile a left ...

感觉越刷越自卑了，不是各种大佬就是各种名校毕业😭

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';