本题,重点考察计算模式。 有一点很重要-->本题,order by不能应用到本题,会报错。 order by 仅能用到 where后边,否则会报错 select b.university, round(count(a.device_id)/count(distinct(b.device_id)),4) avg_answer_cnt from question_practice_detail a inner join user_profile b on a.device_id = b.device_id group by b.university;