一、多对多
学生表
create table students (
id int not null primary key auto_increment,
name varchar(45) not null
)engine=innodb default charset=utf8;
课程表
create table courses (
id int not null primary key auto_increment,
name varchar(45) not null
)engine=innodb default charset=utf8;
中间表
create table stu_cour (
id int not null primary key auto_increment
course_id int not null,
stu_id int not null,
constraint cour foreign key(course_id) references courses(id),
constraint stu foreign key(stu_id) references students(id)
)engine=innodb default charset=utf8;
插入数据
insert into students values (0,"小王");
insert into students values (0,"小宋");
insert into students values (0,"小李");
insert into courses values (0,"语文");
insert into courses values (0,"数学");
insert into courses values (0,"英语");
insert into stu_cour values (0,1,1);
insert into stu_cour values (0,1,2);
insert into stu_cour values (0,1,3);
insert into stu_cour values (0,2,1);
insert into stu_cour values (0,2,3);
insert into stu_cour values (0,3,2);
insert into stu_cour values (0,3,3);
查询学生1选了哪些科目
SELECT courses.id,courses.name FROM courses
INNER JOIN stu_cour ON stu_cour.course_id=courses.id
INNER JOIN students ON students.id= 1
and students.id = stu_cour.stu_id;
查询id=2数学被谁选了
SELECT students.name FROM students
INNER JOIN stu_cour ON stu_cour.stu_id =students.id
INNER JOIN courses ON courses.id= 2
and stu_cour.course_id = courses.id;
