public function orderBy($column, $type = 'asc')
    {
        if (! is_null($this->order)) {
            return $this;
        }

        if (!in_array($type, ['asc', 'desc'])) {
            $type = 'asc';
        }

        $this->order = 'order by `'.$column.'` '.$type;

        return $this;
    }