分为一对多、一对一、多对多。
一对多
dept_id int unsigned comment '归属部门ID'，在员工表添加代码，就能知道属于哪个部门
-- 员工
create table tb_emp (
id int unsigned primary key auto_increment comment 'ID',
username varchar(20) not null unique comment '用户名',
password varchar(32) default '123456' comment '密码',
name varchar(10) not null comment '姓名',
gender tinyint unsigned not null comment '性别, 说明: 1 男, 2 女',
image varchar(300) comment '图像',
job tinyint unsigned comment '职位, 说明: 1 班主任, 2 讲师, 3 学工主管, 4 教研主管',
entrydate date comment '入职时间',
dept_id int unsigned comment '归属部门ID',
create_time datetime not null comment '创建时间',
update_time datetime not null comment '修改时间'
) comment '员工表';
-- 部门
create table tb_dept (
id int unsigned primary key auto_increment comment 'ID',
name varchar(10) not null unique comment '部门名称',
create_time datetime not null comment '创建时间',
update_time datetime not null comment '修改时间'
) comment '部门表';插入数据
-- 插入部门数据
insert into tb_dept (id, name, create_time, update_time) values
(1, '学工部', now(), now()),
(2, '教研部', now(), now()),
(3, '咨询部', now(), now()),
(4, '就业部', now(), now()),
(5, '人事部', now(), now());
-- 插入员工数据
insert into tb_emp (id, username, password, name, gender, image, job, entrydate, dept_id, create_time, update_time) values
(1, 'jinyong', '123456', '金庸', 1, '1.jpg', 4, '2000-01-01', 2, now(), now()),
(2, 'zhangwuji', '123456', '张无忌', 1, '2.jpg', 2, '2015-01-01', 2, now(), now()),
(3, 'yangxiao', '123456', '杨逍', 1, '3.jpg', 2, '2008-05-01', 2, now(), now()),
(4, 'weiyixiao', '123456', '韦一笑', 1, '4.jpg', 2, '2007-01-01', 2, now(), now()),
(5, 'changyuchun', '123456', '常遇春', 1, '5.jpg', 2, '2012-12-05', 2, now(), now()),
(6, 'xiaozhao', '123456', '小昭', 2, '6.jpg', 3, '2013-09-05', 1, now(), now()),
(7, 'jixiaofu', '123456', '纪晓芙', 2, '7.jpg', 2, '2005-08-01', 1, now(), now()),
(8, 'zhouruiruo', '123456', '周芷若', 2, '8.jpg', 2, '2011-11-09', 1, now(), now()),
(9, 'dingminjun', '123456', '丁敏君', 2, '9.jpg', 3, '2011-03-11', 1, now(), now()),
(10, 'zhaomin', '123456', '赵敏', 2, '10.jpg', 1, '2009-02-01', 1, now(), now()),
(11, 'luzhanke', '123456', '鹿杖客', 1, '11.jpg', 2, '2008-08-18', 1, now(), now()),
(12, 'hebiweng', '123456', '鹤笔翁', 1, '12.jpg', 2, now(), 1, now(), now()),
(13, 'fangdongbai', '123456', '方东白', 1, '13.jpg', 2, '2012-11-01', 2, now(), now()),
(14, 'zhangsanfeng', '123456', '张三丰', 1, '14.jpg', 2, '2002-08-01', 2, now(), now()),
(15, 'yulianzhou', '123456', '俞连舟', 1, '15.jpg', 2, '2011-05-01', 2, now(), now()),
(16, 'songyuanqiao', '123456', '宋远桥', 1, '16.jpg', 2, '2010-01-01', 2, now(), now()),
(17, 'chenyouliang', '123456', '陈友谅', 1, '17.jpg', NULL, '2015-03-21', NULL, now(), now());建立连接：外键约束
上面的方法属于物理外键，在企业中一般禁止使用。
一对一
create table tb_user (
id int unsigned primary key auto_increment comment 'ID',
name varchar(10) not null comment '姓名',
gender tinyint unsigned not null comment '性别, 1 男 2 女',
phone char(11) comment '手机号',
degree varchar(10) comment '学历'
) comment '用户信息表';
insert into tb_user values
(1, '白眉鹰王', 1, '18812340001', '初中'),
(2, '青翼蝠王', 1, '18812340002', '大专'),
(3, '金毛狮王', 1, '18812340003', '本科'),
(3, '白龙马王', 1, '18812340003', '本科');创建一对一的外键，可以加上unique来防止重复。
create table tb_user_card (
id int unsigned primary key auto_increment comment 'ID',
nationality varchar(10) not null comment '民族',
birthday date not null comment '生日',
idcard char(18) not null comment '身份证号',
issued varchar(20) not null comment '签发机关',
expire_begin date not null comment '有效期限-开始',
expire_end date comment '有效期限-结束',
user_id int unsigned not null unique comment '用户ID',
constraint fk_user_id foreign key (user_id) references tb_user(id)
) comment '用户信息表';
insert into tb_user_card values
(1, '汉', '1960-11-06', '110000196011060001', '朝阳区公安局', '2000-06-10', null, 1),
(2, '汉', '1970-11-06', '110000197011060002', '南安区公安局', '2005-06-10', '2025-06-10', 2),
(3, '汉', '1963-11-06', '110000196311060003', '吕平区公安局', '2006-06-10', null, 3),
(4, '回', '1980-11-06', '110000198011060004', '海淀区公安局', '2008-06-10', '2028-06-10', 4);多对多
-- 实体表：学生 与 课程
create table tb_student(
id int auto_increment primary key comment '主键ID',
name varchar(10) comment '姓名',
no varchar(10) comment '学号'
) comment '学生表';
insert into tb_student(name, no) values
('熊猫丝', '2000100101'),
('穆迪', '2000100102'),
('股天正', '2000100103'),
('韦一笑', '2000100104');
create table tb_course(
id int auto_increment primary key comment '主键ID',
name varchar(10) comment '课程名称'
) comment '课程表';
insert into tb_course(name) values
('Java'),
('PHP'),
('MySQL'),
('Hadoop');
create table tb_student_course(
id int auto_increment comment '主键' primary key,
student_id int not null comment '学生ID',
course_id int not null comment '课程ID',
constraint fk_courseid foreign key (course_id) references tb_course (id),
constraint fk_studentid foreign key (student_id) references tb_student (id)
) comment '学生课程中间表';
insert into tb_student_course(student_id, course_id) values
(1, 1), (1, 2), (1, 3), (2, 2), (2, 3), (3, 4);
小结
