Sql query in php not returning the value

I am implementing a shopping website for food items. I have a cart for each of my visitor and in the cart, the details of their food items are fed. I have a field called Food_Name in my 'cart' table and I have another table called 'food' where I have Food_Name,Food_Id among other details.

am trying to retrieve the food id by using Food_Name in my cart table and performing a query to get the corresponding food id in my food table. However, I am not getting any result for my food item. The query however works when I hardcode the value of one of my food name for e.g 'Vegetable Gratin' in the place of $foodCommand

Here is part of the code

                $retrieveCart="SELECT * FROM cart WHERE cartNo='$cartNo'";
                $res3=$conn->query($retrieveCart);

                while($rowresult=$res3->fetch(PDO::FETCH_ASSOC))
                {

                    $foodCommand=$rowresult['Food_Name'];

                    echo $foodCommand; //I get the correct food name

                    $retrievefid = "SELECT Food_Id FROM food WHERE Food_Name='$foodCommand'";
                    echo $retrievefid;

                    echo "</br>";

                    $foodresult = $conn->query($retrievefid);
                    $roww= $foodresult->fetch(PDO::FETCH_ASSOC);
                    $fid = $roww['Food_Id'];
                    echo "fid is ".$fid;            
                    $qty=$rowresult['qty'];
                    $fprice=$rowresult['Food_Price'];

                    $odetails="INSERT INTO 
                            visitor_order_details(Food_Id,OV_Id,O_Qty,`Price_Paid(Rs)`) 
                    VALUES('$fid','$vid','$qty','$fprice')";

                        $conn->exec($odetails);

                }//endwhile