$stmt = $pdo->query("SELECT * FROM Product WHERE id=". $productid);
        $row = $stmt->fetch(PDO::FETCH_ASSOC);
        $itemData = array(
            'id' => $row['id'],
            'name' => $row['name'],
            'unitprice' => $row['unitprice'],
            'quantity' => 1
        );

SELECT size FROM ProductDetails where id=".$productid);

$itemData = array(
                'id' => $row['id'],
                'name' => $row['name'],
                'size' => $row['size'],
                'unitprice' => $row['unitprice'],
                'quantity' => 1
            );