对成绩进行排序，名次是连续的的，可出现同名次
sql语句分析理解：
**1.**复制一张表得到b,去，a表中的一个分数进行与b的全部分数进行比较，找出b中大于等于的分数个数，然后去除重复的分数，统计剩余的个数：
(select count(distinct b.Score) from Scores b where b.Score >= a.Score) as “Rank”
**2.**按分数的降序排列，选择Scorce和统计的排名打印出来：
select a.Score as Score,
(select count(distinct b.Score) from Scores b where b.Score >= a.Score) as “Rank”
**3.**最终的结题程序：
select a.Score as Score,
(select count(distinct b.Score) from Scores b where b.Score >= a.Score) as “Rank”
from Scores a
order by a.Score DESC