新手不带IF版本的题解 话说这题好坑,查了好久才发现这question_practice_detail表中的id竟然不是主键还带重复... SELECT res.difficult_level, round(count(qpd.result) / count(res.result), 4) AS correct_rate FROM (SELECT qd.difficult_level, qpd.result, qpd.id, qpd.device_id, qpd.question_id FROM question_practice_detail AS qpd INNER JOIN user_p...