text: DROP DATABASE IF EXISTS employee_tracker;
  CREATE DATABASE employee_tracker;
  USE employee_tracker;
  
  CREATE TABLE departments (
    id int NOT NULL AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    PRIMARY KEY (id)
  );
  
  CREATE TABLE roles (
    id int NOT NULL AUTO_INCREMENT,
    title VARCHAR(50) NOT NULL,
    salary DECIMAL NOT NULL,
    department_id INTEGER,
    CONSTRAINT fk_department FOREIGN KEY (department_id) REFERENCES departments(id) ON DELETE SET NULL,
    PRIMARY KEY (id)
  );
  
  CREATE TABLE employees (
    id int NOT NULL AUTO_INCREMENT,
    first_name VARCHAR(30) NOT NULL,
    last_name VARCHAR(30) NOT NULL, 
    manager_id INTEGER UNSIGNED  DEFAULT NULL,
    role_id INTEGER,
    CONSTRAINT fk_role FOREIGN KEY (role_id) REFERENCES roles(id) ON DELETE SET NULL,
    PRIMARY KEY (id)
  );
  