Question Definition
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.
Java Solution
select case
when id = (select max(id) from seat) and id % 2 = 1 then id
when id % 2 = 0 then id -1
else id + 1 end as id,
student
from seat
order by id asc
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