mysql 计算排名

 

出每个人的排名

SELECT a1.Name, a1.Sales, COUNT(a2.Sales) Sales_Rank 
FROM Total_Sales a1, Total_Sales a2 
WHERE a1.Sales <= a2.Sales OR (a1.Sales=a2.Sales AND a1.Name = a2.Name) 
GROUP BY a1.Name, a1.Sales 
ORDER BY a1.Sales DESC, a1.Name DESC;

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LeetCode上的计算排名：

https://leetcode.com/problems/rank-scores/description/

结果：

方案一：

SELECT
  Score,
  @rank := @rank + (@prev <> (@prev := Score)) Rank
FROM
  Scores,
  (SELECT @rank := 0, @prev := -1) init
ORDER BY Score desc

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解析:方案一中,用了一种简化的判断方式,即 @prev <> (@prev := Score)，
先将 变量 @prev 赋一个值 score,然后 将赋值前和赋值后进行比较，如果赋值前和赋值后相等，则返回0，@rank变量 +0，如果赋值前和赋值后不相等,那么返回1，@rank +1,即分数相同，那么排名也一样。

方案二：

SELECT
  Score,
  (SELECT count(distinct Score) FROM Scores WHERE Score >= s.Score) Rank
FROM Scores s
ORDER BY Score desc

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方案三：

SELECT
  Score,
  (SELECT count(*) FROM (SELECT distinct Score s FROM Scores) tmp WHERE s >= Score) Rank
FROM Scores
ORDER BY Score desc

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方案四：

SELECT s.Score, count(distinct t.score) Rank
FROM Scores s JOIN Scores t ON s.Score <= t.score
GROUP BY s.Id
ORDER BY s.Score desc

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