TP链式操作在group的情况下怎么count

        $list['list'] = $this->join('LEFT JOIN dby_domain ON dby_hospital.id = dby_domain.target_id')->where($where)->group('dby_hospital.id')->select();
        $sql = $this->join('LEFT JOIN dby_domain ON dby_hospital.id = dby_domain.target_id')->where($where)->group('dby_hospital.id')->field('count(*)')->buildsql();
        $list['num'] = D()->table("{$sql} as t")->count();
        return $list;