此结构中的表
teachersstudentscoursesenrollmentsgrades
表结构（SQL）
MySQL 方言的 DDL。在编辑器中打开可获得可编辑的可视化 ER 图，或直接将 SQL 复制到你的项目中。
CREATE TABLE teachers (
id INT PRIMARY KEY AUTO_INCREMENT,
full_name VARCHAR(120) NOT NULL,
email VARCHAR(254) UNIQUE,
hired_at DATE
);
CREATE TABLE students (
id INT PRIMARY KEY AUTO_INCREMENT,
full_name VARCHAR(120) NOT NULL,
email VARCHAR(254) UNIQUE,
enrolled_at DATE
);
CREATE TABLE courses (
id INT PRIMARY KEY AUTO_INCREMENT,
teacher_id INT,
title VARCHAR(200) NOT NULL,
code VARCHAR(20) NOT NULL UNIQUE,
credits INT NOT NULL DEFAULT 3,
FOREIGN KEY (teacher_id) REFERENCES teachers(id)
);
CREATE TABLE enrollments (
id INT PRIMARY KEY AUTO_INCREMENT,
student_id INT NOT NULL,
course_id INT NOT NULL,
enrolled_on DATE NOT NULL,
FOREIGN KEY (student_id) REFERENCES students(id),
FOREIGN KEY (course_id) REFERENCES courses(id)
);
CREATE TABLE grades (
id INT PRIMARY KEY AUTO_INCREMENT,
enrollment_id INT NOT NULL,
letter VARCHAR(2),
score DECIMAL(5,2),
graded_at DATE,
FOREIGN KEY (enrollment_id) REFERENCES enrollments(id)
);