如何在雄辩的orm中结合sum（）和group by语句？

I want to produce record who retrieve data sales in specified date range with 2 parameter input $date_from and $date_to so I am trying to combine some SQL function to do that:

public function print_report(Request $request) {
    $from = "2018-04-03";
    $to = "2018-04-17";
    $data = AppSalesDetail::select('app_sales_detail.*','app_sales.*')
        ->leftJoin('app_sales','app_sales.app_sales_id','=','app_sales_detail.app_sales_id')    
        ->whereBetween('sale_date', array($from, $to))
        ->groupBy("app_sales_detail.app_sales_id")  
        ->sum('app_sales_detail.sub_total')
        ->get();
}

Before I add ->sum('app_sales_detail.sub_total') inside the query everything works fine as my expect but happen this error after I insert that function

Call to a member function groupBy() on string

please give me advice to solve that.

The sum() method only returns one row, you have to add it to select().
You also can't select all the columns:

$data = AppSalesDetail::select('app_sales_detail.app_sales_id')
    ->selectRaw('SUM(sub_total) sub_total')
    ->leftJoin('app_sales','app_sales.app_sales_id','=','app_sales_detail.app_sales_id')    
    ->whereBetween('sale_date', array($from, $to))
    ->groupBy("app_sales_detail.app_sales_id")  
    ->get();