SQL Query: Exchange Seats Problem

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:

• Step1) We get the even id set of student
• Step2) we get the odd id set of student
• Step3) get the even id with odd student name
• step4) get the odd id with even student name
• step5) union and sort step3 and step4

;with even as 
(select * from seat s1 where s1.id%2 = 0)
,odd as 
(select * from seat s2 where s2.id%2 = 1)
,comb as 
(
select e.id, COALESCE(o.student,e.student) as student 
 from even e left join odd o
	on e.id = o.id +1
union all
select o.id, COALESCE(e.student,o.student) as student 
    from odd o left join even e
		on o.id + 1 = e.id
)

select * from comb order by id asc

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