178. 分数排名

## 编写一个 SQL 查询来实现分数排名。 。     
     示例：
    如果两个分数相同，则两个分数排名（Rank）相同。请注意，平分后的下一个名次应该是下一个连续的整数值。换句话说，名次之间不应该有“间隔”。
    
    +----+-------+
    | Id | Score |
    +----+-------+
    | 1  | 3.50  |
    | 2  | 3.65  |
    | 3  | 4.00  |
    | 4  | 3.85  |
    | 5  | 4.00  |
    | 6  | 3.65  |
    +----+-------+
    例如，根据上述给定的 Scores 表，你的查询应该返回（按分数从高到低排列）：
    
    +-------+------+
    | Score | Rank |
    +-------+------+
    | 4.00  | 1    |
    | 4.00  | 1    |
    | 3.85  | 2    |
    | 3.65  | 3    |
    | 3.65  | 3    |
    | 3.50  | 4    |
    +-------+------+
    
`解题思路`

1 distinct count

       select a.Score,
       (select count(distinct Score) from Scores as b where b.Score>=a.Score) as Rank
       from Scores as a order by a.Score desc;
     
2   dense_rank

        `select score, 
                dense_rank() over(order by Score desc) as Rank
         from Scores;`