feature:[MySQL].178.rank scores.

Author: xrksudy

Diff for: README.md

@@ -39,6 +39,7 @@ LeetCode
 | --- | ----------------------------------------------------------------------------------------------------------------------------------- | ---------- | ---------------------------------------------------------------------- |
 | 175 | [Combine Two Tables](https://leetcode.com/problems/combine-two-tables/)                                                             | Easy       | [MySQL](./database/175.combine-two-tables.sql)                         |
 | 176 | [Second Highest Salary](https://leetcode.com/problems/second-highest-salary/description/)                                           | Easy       | [MySQL](./database/176.second-highest-salary.sql)                      |
+| 178 | [Rank Scores](https://leetcode.com/problems/rank-scores/description/)                                                               | Medium     | [MySQL](./database/178.rank-scores.sql)                                |
 | 180 | [Consecutive Numbers](https://leetcode.com/problems/consecutive-numbers/description/)                                               | Medium     | [MySQL](./database/180.consecutive-numbers.sql)                        |
 | 181 | [Employees Earning More Than Their Managers](https://leetcode.com/problems/employees-earning-more-than-their-managers/description/) | Easy       | [MySQL](./database/181.employees-earning-more-than-their-managers.sql) |
 | 182 | [Duplicate Emails](https://leetcode.com/problems/duplicate-emails/description/)                                                     | Easy       | [MySQL](./database/182.duplicate-emails.sql)                           |

Diff for: database/178.rank-scores.sql

@@ -0,0 +1,68 @@
+--
+-- @lc app=leetcode id=178 lang=mysql
+--
+-- [178] Rank Scores
+--
+-- https://leetcode.com/problems/rank-scores/description/
+--
+-- database
+-- Medium (44.63%)
+-- Likes:    758
+-- Dislikes: 139
+-- Total Accepted:    114.3K
+-- Total Submissions: 248.7K
+-- Testcase Example:  '{"headers": {"Scores": ["Id", "Score"]}, "rows": {"Scores": [[1, 3.50], [2, 3.65], [3, 4.00], [4, 3.85], [5, 4.00], [6, 3.65]]}}'
+--
+-- Write a SQL query to rank scores. If there is a tie between two scores, both
+-- should have the same ranking. Note that after a tie, the next ranking number
+-- should be the next consecutive integer value. In other words, there should
+-- be no "holes" between ranks.
+-- 
+-- 
+-- +----+-------+
+-- | Id | Score |
+-- +----+-------+
+-- | 1  | 3.50  |
+-- | 2  | 3.65  |
+-- | 3  | 4.00  |
+-- | 4  | 3.85  |
+-- | 5  | 4.00  |
+-- | 6  | 3.65  |
+-- +----+-------+
+-- 
+-- 
+-- For example, given the above Scores table, your query should generate the
+-- following report (order by highest score):
+-- 
+-- 
+-- +-------+---------+
+-- | score | Rank    |
+-- +-------+---------+
+-- | 4.00  | 1       |
+-- | 4.00  | 1       |
+-- | 3.85  | 2       |
+-- | 3.65  | 3       |
+-- | 3.65  | 3       |
+-- | 3.50  | 4       |
+-- +-------+---------+
+-- 
+-- 
+-- Important Note: For MySQL solutions, to escape reserved words used as column
+-- names, you can use an apostrophe before and after the keyword. For example
+-- `Rank`.
+-- 
+--
+
+-- @lc code=start
+-- Write your MySQL query statement below
+
+SELECT
+  Score,
+  (SELECT count(distinct Score)
+  FROM Scores
+  WHERE Score >= s.Score)
+`Rank`
+FROM Scores s
+ORDER BY Score desc
+
+-- @lc code=end