Method getAllCategoriesByProduct

public static function getAllCategoriesByProduct($productId)
{
    $db = Factory::getDBO();
    // Select stored categories for this ID
    $query = 'SELECT a.category_id' . ' FROM #__phocacart_product_categories AS a' . ' WHERE a.product_id = ' . (int) $productId . ' ORDER BY a.product_id';
    $db->setQuery($query);
    $storedArray = $db->loadColumn();
    return $storedArray;
}