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