如何在SQL数据库中构造两类用户？

CREATE TABLE users (
  user_id INT PRIMARY KEY AUTO_INCREMENT,
  username VARCHAR(50) NOT NULL,
  password VARCHAR(50) NOT NULL,
  email VARCHAR(50) NOT NULL
);

CREATE TABLE roles (
  role_id INT PRIMARY KEY AUTO_INCREMENT,
  role_name VARCHAR(50) NOT NULL
);

CREATE TABLE user_roles (
  user_id INT,
  role_id INT,
  FOREIGN KEY (user_id) REFERENCES users(user_id),
  FOREIGN KEY (role_id) REFERENCES roles(role_id)
);

INSERT INTO users (username, password, email) VALUES ('普通用户', 'password', 'user@example.com');
INSERT INTO users (username, password, email) VALUES ('管理员用户', 'adminpassword', 'admin@example.com');

-- 普通用户角色ID为1，管理员用户角色ID为2
INSERT INTO user_roles (user_id, role_id) VALUES (1, 1);
INSERT INTO user_roles (user_id, role_id) VALUES (2, 2);