Leetcode - 626. Exchange Seats

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 ones seat.

思路：id为奇数则id +1, id为偶数则id-1，且id总数为奇数时，最大id数不变

使用case when语句：

select case when id % 2 = 1 and id != (select count(id) from seat) then id + 1 when id % 2 = 0 then id - 1 else id end as id, student from seat order by id