text: DROP DATABASE IF EXISTS management_db;
  CREATE DATABASE management_db;
  
  USE DATABASE management_db;
  
  CREATE TABLE department (
      id INT PRIMARY KEY,
      name VARCHAR(30) 
  );
  
  CREATE TABLE role (
      id INT AUTO_INCREMENT PRIMARY KEY,
      title VARCHAR(30),
      salary DECIMAL,
      department_id INT,
      FOREIGN KEY (department_id)
      REFERENCES department(id)
      ON DELETE SET NULL
  );
  
  CREATE TABLE employee (
      id INT 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 SET NULL,
  
      FOREIGN KEY (manager_id)
      REFERENCES employee(id)
      ON DELETE SET NULL
  );
  
  manager ID: -- will hold reference to another employee that is the manager of the current employee (null if the employee has no manager)