Exchange Seats 27-10-22

link -------- https://www.codingninjas.com/codestudio/problems/exchange-seats_2119336?topList=top-100-sql-problems&leftPanelTab=0


Problem Statement

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.


----------------- solution ----------------------------------------


select chk as id , student from 
                (select student, case when id % 2 = 0 then id -1
                when id % 2 = 1  and id = counts then id
                when id % 2 = 1 then id+1
                end as chk
            from seat,(select count(*) as counts from seat) as cnt
) as x
order by 1