mysql如何实现多对多关系建模

CREATE TABLE student (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL
);
<p>CREATE TABLE course (
id INT PRIMARY KEY AUTO_INCREMENT,
title VARCHAR(100) NOT NULL
);</p><p>CREATE TABLE student_course (
student_id INT,
course_id INT,
PRIMARY KEY (student_id, course_id),
FOREIGN KEY (student_id) REFERENCES student(id) ON DELETE CASCADE,
FOREIGN KEY (course_id) REFERENCES course(id) ON DELETE CASCADE
);</p>

-- 带附加信息的中间表
CREATE TABLE student_course (
  student_id INT,
  course_id INT,
  enroll_time DATETIME DEFAULT CURRENT_TIMESTAMP,
  grade DECIMAL(3,1),
  PRIMARY KEY (student_id, course_id),
  FOREIGN KEY (student_id) REFERENCES student(id) ON DELETE CASCADE,
  FOREIGN KEY (course_id) REFERENCES course(id) ON DELETE CASCADE
);

SELECT c.title 
FROM course c
JOIN student_course sc ON c.id = sc.course_id
WHERE sc.student_id = 1;

SELECT s.name
FROM student s
JOIN student_course sc ON s.id = sc.student_id
WHERE sc.course_id = 101;

-- 学生1选修课程101
INSERT INTO student_course (student_id, course_id) VALUES (1, 101);

-- 取消学生1对课程101的选修
DELETE FROM student_course WHERE student_id = 1 AND course_id = 101;