text: DROP TABLE IF EXISTS employees;
  DROP TABLE IF EXISTS roles;
  DROP TABLE IF EXISTS departments;
  
  CREATE TABLE departments (
      id INTEGER AUTO_INCREMENT PRIMARY KEY,
      name VARCHAR(30)
  );
  
  CREATE TABLE roles (
      id INTEGER AUTO_INCREMENT PRIMARY KEY,
      title VARCHAR(30),
      salary DECIMAL,
      department_id INTEGER,
      /* Foreign Key constraint*/
      CONSTRAINT fk_department FOREIGN KEY (department_id) REFERENCES departments(id) ON DELETE SET NULL 
  );
  
  CREATE TABLE employees (
      id INTEGER AUTO_INCREMENT PRIMARY KEY,
      first_name VARCHAR(30) NOT NULL,
      last_name VARCHAR (30) NOT NULL,
      role_id INTEGER,
      CONSTRAINT fk_role FOREIGN KEY (role_id) REFERENCES roles(id) ON DELETE SET NULL,
      manager_id INTEGER 
  );