力扣——换座位（数据库的题

Posted 2021-02-07 jaypark

小美是一所中学的信息科技老师，她有一张 seat 座位表，平时用来储存学生名字和与他们相对应的座位 id。

其中纵列的 id 是连续递增的

小美想改变相邻俩学生的座位。

你能不能帮她写一个 SQL query 来输出小美想要的结果呢？

 

示例：

+---------+---------+
|    id   | student |
+---------+---------+
|    1    | Abbot   |
|    2    | Doris   |
|    3    | Emerson |
|    4    | Green   |
|    5    | Jeames  |
+---------+---------+

假如数据输入的是上表，则输出结果如下：

+---------+---------+
|    id   | student |
+---------+---------+
|    1    | Doris   |
|    2    | Abbot   |
|    3    | Green   |
|    4    | Emerson |
|    5    | Jeames  |
+---------+---------+

注意：

如果学生人数是奇数，则不需要改变最后一个同学的座位。

 

# Write your mysql query statement below
SELECT * FROM(
    SELECT id-1 AS id,student FROM seat WHERE id%2=0
    UNION
    SELECT id+1 AS id,student FROM seat WHERE id%2=1 AND (id+1) <= (SELECT COUNT(*) FROM seat)
    UNION
    SELECT id AS id,student FROM seat WHERE id%2=1 AND (id+1) > (SELECT COUNT(*) FROM seat)
) AS T1
ORDER BY id ASC