626. Exchange Seats

Description

Table: Seat

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| student     | varchar |
+-------------+---------+
id is the primary key (unique value) column for this table.
Each row of this table indicates the name and the ID of a student.
The ID sequence always starts from 1 and increments continuously.

 

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.

The 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

Solution 1

MySQL

# Write your MySQL query statement below
SELECT s1.id, COALESCE(s2.student, s1.student) AS student
FROM
    Seat AS s1
    LEFT JOIN Seat AS s2 ON (s1.id + 1) ^ 1 - 1 = s2.id
ORDER BY 1;

Solution 2

MySQL

# Write your MySQL query statement below
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 1;

Solution 3

MySQL

# Write your MySQL query statement below
SELECT
    RANK() OVER (ORDER BY (id - 1) ^ 1) AS id,
    student
FROM Seat;

Solution 4

MySQL

# Write your MySQL query statement below
SELECT
    CASE
        WHEN id & 1 = 0 THEN id - 1
        WHEN ROW_NUMBER() OVER (ORDER BY id) != COUNT(id) OVER () THEN id + 1
        ELSE id
    END AS id,
    student
FROM Seat
ORDER BY 1;

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