-- Курсы
CREATE TABLE courses (
    course_id SERIAL PRIMARY KEY,
    course_name VARCHAR(255) NOT NULL,
    description TEXT,
    start_date DATE,
    end_date DATE
);

-- Студенты
CREATE TABLE students (
    student_id SERIAL PRIMARY KEY,
    first_name VARCHAR(255) NOT NULL,
    last_name VARCHAR(255) NOT NULL,
    email VARCHAR(255) UNIQUE NOT NULL,
    date_of_birth DATE
);

-- Уроки
CREATE TABLE lessons (
    lesson_id SERIAL PRIMARY KEY,
    lesson_name VARCHAR(255) NOT NULL,
    content TEXT,
    video_url VARCHAR(255),
    lesson_order INT
);

-- m2m students to courses
CREATE TABLE student_courses (
    student_id INT REFERENCES students(student_id),
    course_id INT REFERENCES courses(course_id),
    enrollment_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (student_id, course_id)
);