orders-update.php

<?php
    if (session_id() == "" || !isset($_SESSION)) {
        session_start();
    }

    include "config.php";

    if (isset($_SESSION["cart"])) {
        $total = 0;

        foreach ($_SESSION["cart"] as $F_ID => $quantity) {
            $result = $mysqli->query("SELECT * FROM FOOD WHERE id = " . $F_ID);

            if ($result) {
                if ($obj = $result->fetch_object()) {
                    $cost = $obj->price * $quantity;

                    $user = $_SESSION["username"];

                    $query = $mysqli->query(
                        "INSERT INTO orders (product_code, product_name, product_desc, price, units, total, email) VALUES('$obj->product_code', '$obj->product_name', '$obj->product_desc', $obj->price, $quantity, $cost, '$user')"
                    );

                    if ($query) {
                        $newqty = $obj->qty - $quantity;
                        if (
                            $mysqli->query(
                                "UPDATE products SET qty = " .
                                    $newqty .
                                    " WHERE id = " .
                                    $F_ID
                                )
                            ) {
                        }
                    }
                }
            }
        }
    }
    header("location:bill.php");
?>