Problem
Table: Seat
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| id | int |
| student | varchar |
+-------------+---------+
id is the primary key column for this table.
Each row of this table indicates the name and the ID of a student.
id is a continuous increment.
Write an SQL query to swap the seat id of every two consecutive students. If the number of students is odd, the id of the last student is not swapped.
Return the result table ordered by id in ascending order.
The query result format is in the following example.
Example 1:
Input:
Seat table:
+----+---------+
| id | student |
+----+---------+
| 1 | Abbot |
| 2 | Doris |
| 3 | Emerson |
| 4 | Green |
| 5 | Jeames |
+----+---------+
Output:
+----+---------+
| id | student |
+----+---------+
| 1 | Doris |
| 2 | Abbot |
| 3 | Green |
| 4 | Emerson |
| 5 | Jeames |
+----+---------+
Explanation:
Note that if the number of students is odd, there is no need to change the last one's seat.
Solution
# Write your MySQL query statement below
select
id,
case when id % 2 = 1 and lead(student) over (order by id) is null then student
when id % 2 = 1 then lead(student) over (order by id)
else lag(student) over (order by id)
end as student
from seat
order by id asc
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).