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
原文地址:https://www.cnblogs.com/JAYPARK/p/10351175.html
时间: 2024-11-02 15:50:08