Upload 131

Author: ggeerraarrdd

README.md

@@ -163,6 +163,7 @@ The problems and both submitted and site solutions are documented in individual
 | 128   | [Last Person to Fit in the Bus](https://leetcode.com/problems/last-person-to-fit-in-the-bus/description/)                                                     | [Solution](solutions/128_last_person_to_fit_in_the_bus.md)                            | LeetCode    | Medium       | `ORDER BY turn RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW`   |
 | 129   | [Count Salary Categories](https://leetcode.com/problems/count-salary-categories/description/)                                                                 | [Solution](solutions/129_count_salary_categories.md)                                  | LeetCode    | Medium       | `IFNULL`                                                            |
 | 130   | [Employees Whose Manager Left the Company](https://leetcode.com/problems/employees-whose-manager-left-the-company/description/)                               | [Solution](solutions/130_employees_whose_manager_left_the_company.md)                 | LeetCode    | Easy         |                                                                     |
+| 131   | [Exchange Seats](https://leetcode.com/problems/exchange-seats/description/)                                                                                   | [Solution](solutions/131_exchange_seats.md)                                           | LeetCode    | Medium       | `CASE` w/ `LAG` w/ `COALESCE`                                       |
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 ## Author(s)

solutions/131_exchange_seats.md

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+# SQL Everyday \#131
+
+## Exchange Seats
+
+Site: LeetCode\
+Difficulty per Site: Medium
+
+## Problem
+
+Write a solution to swap the seat id of every two consecutive students. If the number of students is odd, the id of the last student is not swapped.
+
+Return the result table ordered by `id` in *ascending* order. [[Full Description](https://leetcode.com/problems/exchange-seats/description/)]
+
+## Submitted Solution
+
+```sql
+-- Submitted Solution
+SELECT 
+    id
+    ,CASE WHEN id % 2 = 0 THEN LAG(student) OVER (ORDER BY id) 
+          ELSE COALESCE(LEAD(student) OVER (ORDER BY id), student)
+          END AS student
+FROM Seat
+;
+```
+
+## Site Solution
+
+```sql
+-- LeetCode Solution 
+-- TBD
+```
+
+## Notes
+
+TBD
+
+## NB
+
+`CASE` w/ `LAG` w/ `COALESCE`
+
+Go to [Table of Contents](/README.md#contents)\
+Go to [Overview](/README.md)