Laravel elokwentna kolumna suma
Product::where('id',$id)->sum('quantity');
hmt
Product::where('id',$id)->sum('quantity');Auth::user()->products->sum('price');
$balance = DB::table('data')->where('user_id' '=' $id)->sum('balance');Auth::user()->products->sum('price');
// And on your App/User.php you need someting like this:
public function products(){
return Products::where('id_buyer', Auth::user()->id)->get();
}