Ps:
sed 分组 （） \1
[root@2f3f5bf6b134 ~]# echo "172.16.153.56" |sed -r 's/([0-9]+).([0-9]+).([0-9]+).56/\1.\3.\2.65/g'
172.153.16.65

多表查询

查询汤师爷所在班的所有学生并且叫他们班级的老师
mysql> select student.name,class.name,teacher.name from student,teacher,class,classteacher where student.class_id=(select student.class_id from student where student.name="汤师爷") and student.class_id=classteacher.class_id and classteacher.teacher_id=teacher.id  and classteacher.class_id=class.id;
+-----------+---------------+--------+
| name      | name          | name   |
+-----------+---------------+--------+
| 六子      | 云计算1901    | 奇哥   |
| 六子      | 云计算1901    | 强哥   |
| 六子      | 云计算1901    | 磊哥   |
| 汤师爷    | 云计算1901    | 奇哥   |
| 汤师爷    | 云计算1901    | 强哥   |
| 汤师爷    | 云计算1901    | 磊哥   |
| 麻匪      | 云计算1901    | 奇哥   |
| 麻匪      | 云计算1901    | 强哥   |
| 麻匪      | 云计算1901    | 磊哥   |
| 黛玉      | 云计算1901    | 奇哥   |
| 黛玉      | 云计算1901    | 强哥   |
| 黛玉      | 云计算1901    | 磊哥   |
+-----------+---------------+--------+

查询黛玉所在班级的老师
mysql> select class.name as "班级",student.name as "学生",teacher.name as "教师" from student,class,teacher,classteacher where student.name="黛玉" and student.class_id=classteacher.class_id and classteacher.teacher_id=teacher.id and classteacher.class_id=class.id;
+---------------+--------+--------+
| 班级          | 学生   | 教师   |
+---------------+--------+--------+
| 云计算1901    | 黛玉   | 奇哥   |
| 云计算1901    | 黛玉   | 强哥   |
| 云计算1901    | 黛玉   | 磊哥   |
| 云计算1902    | 黛玉   | 奇哥   |
| 云计算1902    | 黛玉   | 磊哥   |
+---------------+--------+--------+
5 rows in set (0.01 sec)

连接的关键为外键，
foreign key(class_key) references class(key);
将class表的id字段与该表的class_key相关联。