leetcode Database3

一、Rank Scores

Write a SQL query to rank scores. If there is a tie between two scores, both should have the same ranking. Note that after a tie, the next ranking number should be the next consecutive integer value. In other words, there should be no "holes" between ranks.

+----+-------+
| Id | Score |
+----+-------+
| 1  | 3.50  |
| 2  | 3.65  |
| 3  | 4.00  |
| 4  | 3.85  |
| 5  | 4.00  |
| 6  | 3.65  |
+----+-------+

For example, given the above Scores table, your query should generate the following report (order by highest score):+-------+------+

| Score | Rank |
+-------+------+
| 4.00  | 1    |
| 4.00  | 1    |
| 3.85  | 2    |
| 3.65  | 3    |
| 3.65  | 3    |
| 3.50  | 4    |
+-------+------+
分析：题意为 编写SQL对分数进行排序。如果两个分数相等，其排名应相同。注意在排名相等的分数之后，下一个排名的数值应该连续。换言之，排名之间不应该有“洞”（跳跃）。
思路：使用mysql的自定义变量。

# Write your MySQL query statement below
select Score,Rank from 
(
SELECT Score,
       CASE
           WHEN @dummy <=> Score THEN @Rank := @Rank 
           ELSE @Rank := @Rank +1
    END AS Rank,@dummy := Score as dummy
FROM
  (SELECT @Rank := 0,@dummy := NULL) r,
     Scores
ORDER BY Score DESC
) AS C

或者：

# Write your MySQL query statement below
SELECT Scores.Score, COUNT(Ranking.Score) AS RANK
  FROM Scores
     , (
       SELECT DISTINCT Score
         FROM Scores
       ) Ranking
 WHERE Scores.Score <= Ranking.Score
 GROUP BY Scores.Id, Scores.Score
 ORDER BY Scores.Score DESC;