php oop get sibling method object

Hi guys, I am new to php oop, 

I am trying get an object of sibling method inside a class, seems not working.

here is how i do it.

class Upload extends Base_controller{

 private function sql () {
    $get = Upload::all();
 }
  public function get_index() {
    dd($this->sql()->get);
  }
}