text: 178Rank Scores  对分数排序，同分排名相同，排名之间不跳跃，1234
  表Scores
  +----+-------+
  | Id | Score |
  +----+-------+
  | 1  | 3.50  |
  | 2  | 3.65  |
  | 3  | 4.00  |
  | 4  | 3.85  |
  | 5  | 4.00  |
  | 6  | 3.65  |
  +----+-------+
  返回
  +-------+------+
  | Score | Rank |
  +-------+------+
  | 4.00  | 1    |
  | 4.00  | 1    |
  | 3.85  | 2    |
  | 3.65  | 3    |
  | 3.65  | 3    |
  | 3.50  | 4    |
  +-------+------+
  
  解法一：表一定要有别名，702ms，先得到包含各个分数的表tmp，再从另外一个表中数>=Score的个数作为排名Rank
  SELECT S2.Score,(    
        SELECT COUNT(*)
        FROM (SELECT DISTINCT S1.Score AS s 
              FROM Scores AS S1) AS tmp
        WHERE s >= S2.Score
      ) AS Rank
  FROM Scores AS S2
  ORDER BY S2.Score DESC
  