大师 你这个没必要用子查询嵌套呀, 一个查询就搞定了。 优化了下: select e_r.uid as uid, round(avg(ifnull(score,0)),0) as new_score, round(avg(if(submit_time is not null, timestampdiff(minute, start_time, submit_time), duration)),1) as cost_time from exam_record e_r join examination_info e_i on e_r.exam_id = e_i.exam_id join user_info u_i on e_r.uid = u_i.uid where level = 0 and difficulty = 'hard' group by uid
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