text: DROP DATABASE IF EXISTS employees_db;
  CREATE DATABASE employees_db;
  
  USE employees_db;
  
  CREATE TABLE departments (
      id INT AUTO_INCREMENT NOT NULL,
      department_name VARCHAR(30) NOT NULL,
      PRIMARY KEY (id)
  );
  
  CREATE TABLE roles (
      id INT AUTO_INCREMENT NOT NULL,
      title VARCHAR(30) NOT NULL,
      salary DECIMAL NOT NULL,
      department_id INT NOT NULL,
      PRIMARY KEY (id),
      FOREIGN KEY (department_id) REFERENCES departments(id)
  );
  
  CREATE TABLE employees (
      id INT AUTO_INCREMENT NOT NULL,
      first_name VARCHAR(30) NOT NULL,
      last_name VARCHAR(30) NOT NULL,
      role_id INT NOT NULL,
      manager_id INT,
      PRIMARY KEY (id),
      FOREIGN KEY (role_id) REFERENCES roles(id),
      FOREIGN KEY (manager_id) REFERENCES employees(id)
  );