We will use the efficient MySQL approach: INSERT ... ON DUPLICATE KEY UPDATE .
<a href="products.php">Continue Shopping</a> <a href="checkout.php">Proceed to Checkout</a> <?php endif; ?> add-cart.php num
// initialize cart if (!isset($_SESSION['cart'])) $_SESSION['cart'] = []; We will use the efficient MySQL approach: INSERT
: Sends the user back to the product page or the cart view, often using a header redirect or a JSON response if using AJAX. Common Code Structure Proceed to Checkout<