text: -- Delete existing tables
  DROP TABLE IF EXISTS employees;
  DROP TABLE IF EXISTS roles;
  DROP TABLE IF EXISTS departments;
  
  -- Create a 'department' table
  CREATE TABLE department (
      id INTEGER AUTO_INCREMENT PRIMARY KEY,
      dept_name VARCHAR(50) NOT NULL
  );
  
  -- Create a 'role' table
  CREATE TABLE role (
      id INTEGER AUTO_INCREMENT PRIMARY KEY,
      title VARCHAR(30) NOT NULL,
      salary DECIMAL(10,2) NOT NULL,
      department_id INTEGER,
      FOREIGN KEY (department_id) REFERENCES department(id) ON DELETE SET NULL
  );
  
  -- Create an 'employee' table
  CREATE TABLE employee (
      id INTEGER AUTO_INCREMENT PRIMARY KEY,
      first_name VARCHAR(30) NOT NULL,
      last_name VARCHAR(30) NOT NULL,
      role_id INTEGER,
      FOREIGN KEY (role_id) REFERENCES role(id) ON DELETE SET NULL,
      manager_id INTEGER,
      FOREIGN KEY (manager_id) REFERENCES employee(id) ON DELETE SET NULL
  );