Added Rank Scores

Author: ignacio-chiazzo

LeetcodeProblems/Databases/Rank_Scores.sql

@@ -0,0 +1,56 @@
+/* 
+Rank Scores
+https://leetcode.com/problems/rank-scores/
+
+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`.
+*/
+
+-- Solution 1
+SELECT Scores.Score, t3.Rank
+FROM Scores JOIN (
+    select Score, (@inc := @inc + 1) as "Rank"
+    FROM (
+        SELECT Score as Score
+        FROM Scores
+        GROUP BY Score
+        ORDER BY Score DESC
+    ) AS t1 CROSS JOIN  (SELECT @inc := 0 ) as t2
+) as t3 ON Scores.Score = t3.Score
+ORDER BY t3.Rank ASC
+
+
+-- Solution 2
+-- Set two variables, one to keep the previous Score and other to keep the current Rank
+SELECT Score,
+    @curr := CASE WHEN @previous = (@previous := Score) THEN 
+        CAST(@curr AS SIGNED INTEGER)
+        ELSE 
+        CAST(@curr + 1 AS SIGNED INTEGER)
+    END AS "Rank"
+FROM Scores, (SELECT @curr := 0, @previous := -1) as t1
+ORDER BY SCORE DESC
+

README.md

@@ -81,6 +81,7 @@ To run a specific problem in your console, go to the file test, add the call to
 ### Databases
 | Problems | Level | Link |
 |-|-|-|
+| [Rank Scores](/LeetcodeProblems/Databases/Rank_Scores.sql) | Medium | https://leetcode.com/problems/rank-scores/ |
 | [Consecutive Numbers](/LeetcodeProblems/Databases/Consecutive_Numbers.sql) | Medium | https://leetcode.com/problems/consecutive-numbers |
 | [Department Highest Salary](/LeetcodeProblems/Databases/Department_Highest_Salary.sql) | Medium | https://leetcode.com/problems/department-highest-salary |
 | [Exchange Seats](/LeetcodeProblems/Databases/Exchange_Seats.sql) | Medium | https://leetcode.com/problems/exchange-seats |