README_EN.md

626. Exchange Seats

中文文档

Description

Table: Seat

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| name        | varchar |
+-------------+---------+
id is the primary key column for this table.
Each row of this table indicates the name and the ID of a student.
id is a continuous increment.

 

Write an SQL query 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.

The query result format is in the following example.

 

Example 1:

Input: 
Seat table:
+----+---------+
| id | student |
+----+---------+
| 1  | Abbot   |
| 2  | Doris   |
| 3  | Emerson |
| 4  | Green   |
| 5  | Jeames  |
+----+---------+
Output: 
+----+---------+
| id | student |
+----+---------+
| 1  | Doris   |
| 2  | Abbot   |
| 3  | Green   |
| 4  | Emerson |
| 5  | Jeames  |
+----+---------+
Explanation: 
Note that if the number of students is odd, there is no need to change the last one's seat.

Solutions

SQL

SELECT
	s1.id,
	COALESCE ( s2.student, s1.student ) AS student
FROM
	seat s1
	LEFT JOIN seat s2 ON ( s1.id + 1 ) ^ 1 - 1 = s2.id
ORDER BY
	s1.id;

SELECT
    id + (
        CASE
            WHEN id % 2 = 1 AND id != (SELECT MAX(id) FROM seat) THEN 1
			WHEN id % 2 = 0 THEN -1
			ELSE 0
		END
    ) AS id,
    student
FROM
    seat
ORDER BY
	id;