mySQL排名（并提取）

Question

下周末我们将举行一场半决赛和决赛的三项比赛。只有最好的15名参赛者才能参加半决赛。总决赛只有最佳6人参赛。

的资格你从0到100的得分为每个资格

我期待找到一种方法来选择半决赛的参赛选手。这应该是基于（qualification1的等级）*（qualification2的等级）*（qualification3的排名）

，所以我需要的东西，如：

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 

当然，但这不是有效的MySQL。

此外，如果寿参赛选手具有相同的比分，他们应该都包含在半决赛即使这超过了最大的15

决赛这个问题，我们要选择最好的6的半决赛比分。如果分数是一样的，我们希望在资格选择..

Answer 1

选项1：使用的Postgres，支持窗口函数（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：具有分数X的用户的排名是（1+分数小于X的用户的计数（*））;这很可能是相当缓慢

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 

编辑

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;