怎么在dcat后台自定义数据排序

$grid->column('success_count','收益')
                    ->display(function() {
                        $success_count = UserApply::where('user_id', $this->id)
                                        ->where('status', 2)
                                        ->sum('applyNum');

                        return number_format($success_count,2);

                    })->sortable();

要怎么写才能在后台按这个排序呢？现在只能显示出来，排序会报错

select * from `users` order by `success_count` desc limit 20 offset 220