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;