mysql怎么建立关联

CREATE TABLE `user` (
  `id` INT PRIMARY KEY,
  `username` VARCHAR(50) NOT NULL
);

CREATE TABLE `user_detail` (
  `id` INT PRIMARY KEY,
  `user_id` INT UNIQUE NOT NULL,
  `address` VARCHAR(255),
  FOREIGN KEY (`user_id`) REFERENCES `user`(`id`)
);

CREATE TABLE `department` (
  `id` INT PRIMARY KEY,
  `name` VARCHAR(50) NOT NULL
);

CREATE TABLE `employee` (
  `id` INT PRIMARY KEY,
  `name` VARCHAR(50) NOT NULL,
  `department_id` INT,
  FOREIGN KEY (`department_id`) REFERENCES `department`(`id`)
);

CREATE TABLE `student` (
  `id` INT PRIMARY KEY,
  `name` VARCHAR(50) NOT NULL
);

CREATE TABLE `course` (
  `id` INT PRIMARY KEY,
  `name` VARCHAR(50) NOT NULL
);

CREATE TABLE `student_course` (
  `student_id` INT,
  `course_id` INT,
  PRIMARY KEY (`student_id`, `course_id`),
  FOREIGN KEY (`student_id`) REFERENCES `student`(`id`),
  FOREIGN KEY (`course_id`) REFERENCES `course`(`id`)
);