-- 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 one's seat.

-- # Write your MySQL query statement below

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