mysql 多表唯一主键

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

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

-- 使用 INSERT IGNORE
INSERT IGNORE INTO student_courses (student_id, course_id) VALUES (1, 1);

-- 使用 ON DUPLICATE KEY UPDATE
INSERT INTO student_courses (student_id, course_id) 
VALUES (1, 1) 
ON DUPLICATE KEY UPDATE student_id = student_id;

CREATE INDEX idx_student_course ON student_courses (student_id, course_id);