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?
代码语言：javascript复制 --------- ---------
| id | student |
--------- ---------
| 1 | Abbot |
| 2 | Doris |
| 3 | Emerson |
| 4 | Green |
| 5 | Jeames |
--------- --------- For the sample input, the output is:
代码语言：javascript复制 --------- ---------
| 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
代码语言：javascript复制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;
