mySQL排名（並提取）

Question

下週末我們將舉行一場半決賽和決賽的三項比賽。只有最好的15名參賽者才能參加半決賽。總決賽只有最佳6人蔘賽。

的資格你從0到100的得分爲每個資格

我期待找到一種方法來選擇半決賽的參賽選手。這應該是基於（qualification1的等級）*（qualification2的等級）*（qualification3的排名）

，所以我需要的東西，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 

當然，但這不是有效的MySQL。

此外，如果壽參賽選手具有相同的比分，他們應該都包含在半決賽即使這超過了最大的15

決賽這個問題，我們要選擇最好的6的半決賽比分。如果分數是一樣的，我們希望在資格選擇..

Answer 1

選項1：使用的Postgres，支持窗口函數（即RANK（）和DENSE_RANK（））

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

選項2：使用自聯接：具有分數X的用戶的排名是（1+分數小於X的用戶的計數（*））;這很可能是相當緩慢

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 

選項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 

編輯

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;