题解 | #每类试卷得分前3名#

select * from(
    select
    tag as tid,
    uid,
    ROW_NUMBER()OVER(PARTITION BY tag ORDER BY max(score) desc,min(score) desc,uid desc) ranking
from
    examination_info
    join exam_record using (exam_id)
    group by tid,uid) as newform
where newform.ranking <= 3

本题难度是比较大的，必须取row_number()over()来计算每行的排列顺序，用partion by tag来根据标签进行排序,由于是有group by 关键词所以排序规则只能选择uid或者tag，或者min(）max(）函数去取值。