Question

下周末我们将参加一场半决赛和决赛的3项资格赛。只有最好的15名参赛者才能参加半决赛。只有最好的6人参加总决赛。

在资格证书中，每个资格证书的分数从0到100

我正在寻找一种方法来选择半决赛的比赛者。这应该基于（资格等级1）*（资格等级2）*（资格等级3）

所以我需要这样的东西：

select id, name, ((.... as RANK_OF_SCORE_1) * (.. as RANK_OF_SCORE_2) * (... as     RANK_OF_SCORE_3)) as qualification_score from participants order by qualification_score desc limit 15

但当然这不是有效的mySQL。

除了这个问题，如果比赛者得分相同，即使超过15的最高分，他们也应该被列入半决赛。

对于决赛，我们希望选择半决赛中最好的6分。如果2个分数相同，我们希望选择资格..

Answer 1

选项1：使用支持窗口函数的postgres（即RANK（）和DENSE_RANK（））

SELECT user_id, score, rank() over (order by score desc) from scores;
Time : 0.0014 s

选项2：使用自联接：得分为X的用户的等级为（1 +得分小于X的用户的计数（*））;这可能很慢

CREATE TABLE scores( user_id INT PRIMARY KEY, score INT, KEY(score) );
INSERT INTO scores SELECT id, rand()*100 FROM serie LIMIT 1000;

SELECT a.user_id, a.score, 1+count(b.user_id) AS rank 
    FROM scores a 
    LEFT JOIN scores b ON (b.score>a.score) 
    GROUP BY user_id ORDER BY rank;

+---------+-------+------+
| user_id | score | rank |
+---------+-------+------+
|     381 |   100 |    1 |
|     777 |   100 |    1 |
|     586 |   100 |    1 |
|     907 |   100 |    1 |
|     790 |   100 |    1 |
|     253 |    99 |    6 |
|     393 |    99 |    6 |
|     429 |    99 |    6 |
|     376 |    99 |    6 |
|     857 |    99 |    6 |
|     293 |    99 |    6 |
|     156 |    99 |    6 |
|     167 |    98 |   13 |
|     594 |    98 |   13 |
|     690 |    98 |   13 |
|     510 |    98 |   13 |
|     436 |    98 |   13 |
|     671 |    98 |   13 |

time 0.7s

选项3：

SET @rownum = 0;
SELECT a.user_id, a.score, b.r FROM
scores a
JOIN (
    SELECT score, min(r) AS r FROM (
        SELECT user_id, score, @rownum:=@rownum+1 AS r 
        FROM scores ORDER BY score DESC
    ) foo GROUP BY score
) b USING (score)
ORDER BY r;

time : 0.0014 s

修改

SET @rownum1 = 0;
SET @rownum2 = 0;
SET @rownum3 = 0;

SELECT s.*, s1.r, s2.r, s3.r FROM
scores s
JOIN
(
    SELECT score_1, min(r) AS r FROM (
        SELECT score_1, @rownum1:=@rownum1+1 AS r 
        FROM scores ORDER BY score_1 DESC
    ) foo GROUP BY score_1
) s1 USING (score_1) JOIN (
    SELECT score_2, min(r) AS r FROM (
        SELECT score_2, @rownum2:=@rownum2+1 AS r 
        FROM scores ORDER BY score_2 DESC
    ) foo GROUP BY score_2
) s2 USING (score_2) JOIN (
    SELECT score_3, min(r) AS r FROM (
        SELECT score_3, @rownum3:=@rownum3+1 AS r 
        FROM scores ORDER BY score_3 DESC
    ) foo GROUP BY score_3
) s3 USING (score_3)
ORDER BY s1.r * s2.r * s3.r;

mySQL排名（和绘制）

1 个答案: