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