leetcode（178） 分数排名

方法一：
分情况，再连接：

# Write your MySQL query statement below
SELECT S1.Score,
(
    SELECT COUNT(DISTINCT S2.Score)
    FROM Scores S2
    WHERE S2.Score>=S1.Score
)AS Rank
FROM Scores S1
ORDER BY Score DESC
;

方法二：
自连接：

# Write your MySQL query statement below
SELECT S1.Score, 
       COUNT(DISTINCT S2.Score) AS Rank 
FROM Scores S1,Scores S2
WHERE S2.Score>=S1.Score
GROUP BY S1.Id
ORDER BY S1.Score DESC
;