solve problem Rank Score

Author: P-ppc

README.md

@@ -332,4 +332,5 @@ All solutions will be accepted!
 |197|[Rising Temperature](https://leetcode-cn.com/problems/rising-temperature/description/)|[mysql](./database/RisingTemperature)|Easy|
 |181|[Employees Earning More Than Their Managers](https://leetcode-cn.com/problems/employees-earning-more-than-their-managers/description/)|[mysql](./database/EmployeesEarningMoreThanTheirManagers)|Easy|
 |176|[Second Highest Salary](https://leetcode-cn.com/problems/second-highest-salary/description/)|[mysql](./database/SecondHighestSalary)|Easy|
-|626|[Exchange Seats](https://leetcode-cn.com/problems/exchange-seats/description/)|[mysql](./database/ExchangeSeats)|Medium|
+|626|[Exchange Seats](https://leetcode-cn.com/problems/exchange-seats/description/)|[mysql](./database/ExchangeSeats)|Medium|
+|178|[Rank Scores](https://leetcode-cn.com/problems/rank-scores/description/)|[mysql](./database/RankScore)|Medium|

database/RankScore/README.md

@@ -0,0 +1,2 @@
+# Rank Score
+We can solve this problem by sub-query

database/RankScore/solution.sql

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+# Write your MySQL query statement below
+select s.Score, 
+    (select count(distinct Score) from Scores where Score >= s.Score) as Rank 
+from Scores as s order by Score desc