Question

626. Exchange Seats

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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.
id is a continuous increment.

 

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

# 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

# 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

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

Solution 4

# 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;