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.
# Write your MySQL query statement below
SELECT
s.id,
s.student
FROM
(
SELECT
id - 1 AS id,
student
FROM
seat
WHERE
(id % 2 = 0)
UNION
SELECT
(CASE WHEN (cnt%2=1) AND id=cnt THEN id ELSE id + 1 END) AS id,
student
FROM
seat,
(select count(*) as cnt from seat) as seatcnt
WHERE
(id % 2 = 1)
) s
GROUP BY
s.id ASC