换座位

注意：如果学生人数为奇数，则不需要改变最后一个同学的座位

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