text: DROP TABLE IF EXISTS employee;
  DROP TABLE IF EXISTS role;
  DROP TABLE IF EXISTS department;
  CREATE TABLE department (
    id INTEGER NOT NULL AUTO_INCREMENT,
    name VARCHAR(30) NOT NULL,
    PRIMARY KEY (id)
  );
  CREATE TABLE role (
    id INTEGER NOT NULL AUTO_INCREMENT,
    title VARCHAR(30) NOT NULL,
    salary decimal NOT NULL,
    department_id INTEGER NOT NULL,
    PRIMARY KEY (id),
    CONSTRAINT fk_department FOREIGN KEY (department_id) REFERENCES department(id)
    /*ON DELETE SET NULL*/
  );
  CREATE TABLE employee (
    id INTEGER NOT NULL AUTO_INCREMENT,
    first_name VARCHAR(30) NOT NULL,
    last_name VARCHAR(30) NOT NULL,
    role_id integer,
    manager_id integer,
    PRIMARY KEY (id),
    CONSTRAINT fk_role FOREIGN KEY (role_id) REFERENCES role(id) ON DELETE
    SET NULL,
      CONSTRAINT fk_manager FOREIGN KEY (manager_id) REFERENCES employee(id)
      /*ON DELETE SET NULL*/
  );