写了一个冗余的版本,但为什么报错呢,不理解。。。select device_id,university,count(question_id) question_cnt,sum(res) right_question_cnt from (select u.device_id,u.university,qp.question_id, qp.result,IF(qp.result='right',1,0)) as res from user_profile u left join question_practice_detail qp on device_id where month(qp.d...