public function exportExcel(){ 
        Excel::create('訂單統計'.date('Y-m-d H_i_s'), function ($excel) {
            $excel->sheet('order', function ($sheet) {
                
                    $data = Orders::where('type',2)->orderby('id','desc')->get(); //要用get()
                    $sheet->appendRow(['老師姓名','聯絡方式','老師性別']);//這裡是表頭的名稱
                    foreach($data as $o){ //appendRow是匯出一行，要匯出資料表就要迴圈這個
                        $sheet->appendRow([$o->teacher_name,(string)$o->teacher_mobile,$o->teacher_sex]);//進行迴圈
                    }
                

            });
        })->download('csv');
        
    }