Added Exchange Seats

Author: ignacio-chiazzo

LeetcodeProblems/Databases/Exchange_Seats.sql

@@ -0,0 +1,48 @@
+/*
+Exchange Seats
+https://leetcode.com/problems/exchange-seats/
+
+Mary is a teacher in a middle school and she has a table seat storing students' names and their corresponding seat ids.
+
+The column id is continuous increment.
+
+Mary wants to change seats for the adjacent students.
+Can you write a SQL query to output the result for Mary?
+
++---------+---------+
+|    id   | student |
++---------+---------+
+|    1    | Abbot   |
+|    2    | Doris   |
+|    3    | Emerson |
+|    4    | Green   |
+|    5    | Jeames  |
++---------+---------+
+For the sample input, the output is:
+ 
+
++---------+---------+
+|    id   | student |
++---------+---------+
+|    1    | Doris   |
+|    2    | Abbot   |
+|    3    | Green   |
+|    4    | Emerson |
+|    5    | Jeames  |
++---------+---------+
+Note:
+If the number of students is odd, there is no need to change the last one's seat.
+*/
+
+WITH paresAImpares AS (
+    SELECT (id - 1) AS id, student
+    FROM seat
+    WHERE MOD(id, 2) = 0
+), imparesAPares AS (
+    SELECT (id + 1) as id, student
+    FROM seat
+    WHERE MOD(id, 2) = 1
+)
+
+SELECT id, coalesce(paresAImpares.student, imparesAPares.student, seat.student) AS student
+FROM seat LEFT JOIN paresAImpares USING(id) LEFT JOIN imparesAPares using(id)

README.md

@@ -81,12 +81,12 @@ To run a specific problem in your console, go to the file test, add the call to
 ### Databases
 | Problems | Level | Link |
 |-|-|-|
+| [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 |
+| [Nth Highest Salary](/LeetcodeProblems/Databases/nth_Highest_Salary.sql) | Medium | https://leetcode.com/problems/nth-highest-salary |
 | [Combine Two Tables](/LeetcodeProblems/Databases/Combine_Two_Tables.sql) | Easy   | https://leetcode.com/problems/combine-two-tables |
 | [Second Highest Salary](/LeetcodeProblems/Databases/Second_highest_salary.sql)| Easy   | https://leetcode.com/problems/second-highest-salary |
-| [Nth Highest Salary](/LeetcodeProblems/Databases/nth_Highest_Salary.sql) | Medium | https://leetcode.com/problems/nth-highest-salary |
 | [Customers Who Never Order](/LeetcodeProblems/Databases/Customers_Who_Never_Order.sql)| Easy |  https://leetcode.com/problems/customers-who-never-order |
-| [Department Highest Salary](/LeetcodeProblems/Databases/Department_Highest_Salary.sql) | Medium | https://leetcode.com/problems/department-highest-salary/ |
-
 
 ### UtilsClasses