text: CREATE TABLE students (
    id            INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1),
    first_name    VARCHAR(30),
    last_name     VARCHAR(50),
    PRIMARY KEY (id)
  );
  
  CREATE TABLE classes (
    code          VARCHAR(15) NOT NULL,
    title         VARCHAR(30),
    description   VARCHAR(250),
    PRIMARY KEY (code)
  );
  
  CREATE TABLE students_classes (
    student_id    INTEGER,
    class_code    VARCHAR(15),
    PRIMARY KEY (student_id, class_code),
    CONSTRAINT student_fk  FOREIGN KEY (student_id) REFERENCES students (id) ON DELETE CASCADE,
    CONSTRAINT classes_fk  FOREIGN KEY (class_code) REFERENCES classes (code) ON DELETE CASCADE
  );