关于mysqli query的插入语句

 if(mysqli_query($x,"INSERT INTO users(username, password,) VALUES（'"&$username&"', '"&$password&"')")){

 echo "<script>alert('注册成功');window.location.href='users.php';</script>";

 }else{

  echo "<script>alert('注册失败');window.location.href='users.php';</script>";

请大神帮忙看下哪里错了