mysql 修改多对多关系表

CREATE TABLE students (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(100)
);

CREATE TABLE courses (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(100)
);

CREATE TABLE student_courses (
    student_id INT,
    course_id INT,
    PRIMARY KEY (student_id, course_id),
    FOREIGN KEY (student_id) REFERENCES students(id),
    FOREIGN KEY (course_id) REFERENCES courses(id)
);

DELETE FROM student_courses WHERE student_id = 1 AND course_id = 101;

INSERT INTO student_courses (student_id, course_id) VALUES (1, 102);

ALTER TABLE student_courses
ADD CONSTRAINT fk_student
FOREIGN KEY (student_id) REFERENCES students(id)
ON DELETE CASCADE;

ALTER TABLE student_courses
ADD CONSTRAINT fk_course
FOREIGN KEY (course_id) REFERENCES courses(id)
ON DELETE CASCADE;

CREATE INDEX idx_student_courses ON student_courses(student_id, course_id);