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。
用union,直接考虑三种情况:
# Write your MySQL query statement below
select p.id,p.student from(
select id+1 as id,student from seat where id%2=1 and id!=(select count(*) from seat)
union select id-1 as id,student from seat where id%2=0
union select id,student from seat where id%2=1 and id=(select count(*)from seat)
)p order by id