Exchange Seats

Desicription

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?

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+---------+---------+
| id | student |
+---------+---------+
| 1 | Abbot |
| 2 | Doris |
| 3 | Emerson |
| 4 | Green |
| 5 | Jeames |
+---------+---------+

For the sample input, the output is:

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+---------+---------+
| 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

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select
if(id = (select count(*) from seat), if(id % 2 = 0, id - 1, id), if(id % 2 = 0, id - 1, id + 1)) as id, student from seat order by id;