text: DROP DATABASE IF EXISTS employees;
  CREATE DATABASE employees;
  
  USE employees;
  
  DROP TABLE IF EXISTS department;
  CREATE TABLE department (
      id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
      name VARCHAR(30)
  );
  
  DROP TABLE IF EXISTS role;
  CREATE TABLE role (
      id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
      title VARCHAR(30),
      salary DECIMAL NOT NULL,
      department_id INT,
      FOREIGN KEY(department_id)
      REFERENCES department(id)
      ON DELETE SET NULL
  );
  
  DROP TABLE IF EXISTS employee;
  CREATE TABLE employee (
      id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
      first_name VARCHAR(30),
      last_name VARCHAR(30),
      role_id INT,
  	manager_id INT,
      FOREIGN KEY(role_id)
      REFERENCES role(id)
      ON DELETE CASCADE,
  	FOREIGN KEY(manager_id)
      REFERENCES employee(id)
      ON DELETE SET NULL
  );