MySQL数据库——多表查询（1）-多表关系（一对多、多对对多、一对一）、多表查询概述（概念、笛卡尔积、分类）

create table 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 student (name,no)
    values ('黛绮丝','2000100101'),('谢逊','2000100102'),('殷天正','2000100103'),('韦一笑','2000100104');
 
create table 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 course (name)
    values ('Java'),('PHP'),('MySQL'),('Hadoop');
 
create table student_course(
    id int auto_increment primary key  comment '主键',
    studentid int not null comment '学生ID',
    courseid int not null  comment '课程ID',
    constraint fk_courseid foreign key (courseid) references  course (id),
    constraint fk_student foreign key  (studentid) references  student (id)
)comment '学生课程中间表';
insert into student_course (studentid, courseid)
    values (1,1),(1,2),(1,3),(2,2),(2,3),(3,4);

1. creacreate table tb_user(
    id int auto_increment primary key  comment '主键ID',
    name varchar(10) comment '姓名',
    age int comment '年龄',
    gender char(1) comment '1:男,2:女',
    phone char(11) comment '手机号'
)comment '用户基本信息表';
 
create table tb_user_edu(
    id int auto_increment primary key comment '主键ID',
    degree varchar(20) comment'学历',
    major varchar(50) comment '专业',
    primaryschool varchar(50) comment '小学',
    middleschool varchar(50) comment '中学',
    university varchar(50) comment '大学',
    userid int unique comment '用户ID',
    constraint fk_userid foreign key (userid) references tb_user (id)
)comment '用户教育信息表';
 
insert into tb_user(id, name, age, gender, phone)
    values (null, '黄渤' ,45, '1', '1800001111'),
           (null, '冰冰' ,35, '2' , '1800002222'),
           (null, '码云',55, '1', '1800008888'),
           (null, '李彦宏' ,50, '1', '1800009999');
 
insert into tb_user_edu (id, degree, major, primaryschool, middleschool, university, userid)
    values (null,'本科','舞蹈','静安区第一小学', '静安区第-中学', '北京舞蹈学院',1),
           (null, '硕士','表演','朝阳区第小学','朝阳区第一中学', '北京电影学院' ,2),
           (null,'本科','英语','杭州市第小学','杭州市第一中学','杭州师范大学',3),
           (null, '本科','应用数学','阳泉第一小学','阳泉区第一中学','清华大学',4);

select * from emp,dept;

select * from emp,dept where emp.dept_id = dept.id;