题解 | #每类试卷得分前3名#

SELECT
    tid,
    uid,
    ranking
FROM (
    SELECT
        tid,
        uid,
        RANK() OVER(PARTITION BY tid ORDER BY max_score DESC, min_score DESC, uid DESC) AS ranking
    FROM (
        SELECT
            ei.tag AS tid,
            er.uid AS uid,
            min(er.score) AS min_score,
            max(er.score) AS max_score
        FROM examination_info ei JOIN exam_record er 
                ON ei.exam_id = er.exam_id
        GROUP BY ei.tag, er.uid
    ) T
) TT
WHERE TT.ranking <= 3
ORDER BY tid, ranking

1. 第一个子查询（内层），求出每个科目、每个用户的最小/最大分数，用于后期排名
2. 第二个子查询（中层），按题目要求算出排名
3. 外层查询，显示前三名的信息