MySQL组织表设计_mysql表的设计
宋利兴__2011/09/13
select[distinct]列名….from表名
注意事项
可以替代列名, 表示所有列, 但是通常我们为了提高代码的可读性, 不使用*
DISTINCT为过滤重复记录
1. 表的设计
1.1. 单独的实体
public class User{
private int id;
private String name;
private int age;
}
user
id
name
age
1
张三
18
2
李四
20
3
王五
19
1.2. 一对多、多对一
foreign key
public class Employee {
private int id;
private String name;
private Department department;
}
public class Department {
private int id;
private String name;
private Set employees;
}
一对多
多对一
department employee
id
name
1
开发部
2
市场部
id
name
department_id
1
张三
1
2
李四
1
3
王五
2
多的一方设置外键
create table department(
id int primary key auto_increment,
name varchar(20)
);
create table employee(
id int primary key auto_increment,
name varchar(20),
department_id int,
constraint department_id_fk foreign key(department_id) references department(id)
);
insert into department(name) values('开发部');
insert into department(name) values('市场部');
insert into employee(name, department_id) values('张三',1);
insert into employee(name, department_id) values('李四',1);
insert into employee(name, department_id) values('王五',2);
1.3. 一对一
public class Husband {
private int id;
private String name;
private Wife wife;
}
public class Wife {
private int id;
private String name;
private Husband husband;
}
一对一
foreign key
unique husband wife
id
name
1
张三
2
李四
id
name
husband_id
1
冰冰
2
2
志玲
1
独立外键, 没有依赖关系, 两个表的对象都可以独立存在.
create table husband(
id int primary key auto_increment,
name varchar(20)
);
create table wife(
id int primary key auto_increment,
name varchar(20),
husband_id int,
constraint husband_id_fk foreign key(husband_id) references husband(id)
);
insert into husband(name) values('张三');
insert into husband(name) values('李四');
insert into wife(name, husband_id) values('冰冰',2);
insert into wife(name, husband_id) values('志玲',1);
public class Person {
private int id;
private String name;
private IdCard idCard;
}
public class IdCard {
private int id;
private String num;
private Person person;
}
一对一
foreign key
person idcard
id
name
1
张三
2
李四
id
num
2
110123199009091234
1
120123200001011234
主键即外键, 分为主表和从表, 从表依赖于主表, 从表中的对象不能单独存在.
注意从表的主键, 不能自动增长.
create table person (
id int primary key auto_increment,
name varchar(20)
);
create table idcard (
id int primary key,
num varchar(20),
constraint id_fk foreign key(id) references person(id)
);
insert into person(name) values('张三');
insert into person(name) values('李四');
insert into idcard(id,num) values(2,'110123199009091234');
insert into idcard(num,id) values('110123199009091234', 1);
1.4. 多对多
public class Student {
private int id;
private String name;
private Set teachers;
}
public class Teacher {
private int id;
private String name;
private Set students;
}
多对多
foreign key
foreign key
student student_teacher teacher
id
name
1
张三
2
李四
3
王五
student_id
teacher_id
1
1
2
1
2
2
3
2
id
name
1
张孝祥
2
黎活明
用一张关系表保存多对多的关系, 有两列分别引用两张表的主键, 并且这两列组合起来成为联合主键
create table student (
id int primary key auto_increment,
name varchar(20)
);
create table teacher (
id int primary key auto_increment,
name varchar(20)
);
create table student_teacher(
student_id int,
teacher_id int,
primary key(student_id, teacher_id),
constraint student_id_fk foreign key(student_id) references student(id),
constraint teacher_id_fk foreign key(teacher_id) references teacher(id)
);
insert into student(name) values('张三');
insert into student(name) values('李四');
insert into student(name) values('王五');
insert into teacher(name) values('zxx');
insert into teacher(name) values('lhm');
insert into student_teacher values(1,1);
insert into student_teacher values(2,1);
insert into student_teacher values(2,2);
insert into student_teacher values(3,2);