public function findAllBySku($sku)
    {

        // prepare the params
        $params = array(MemberNames::SKU => $sku);

        // initialize the array for the category product relations
        $categoryProducts = array();

        // load and return the product category relation for the passed product SKU
        $this->categoryProductsBySkuStmt->execute($params);

        // prepare the result by using the category ID as key
        foreach ($this->categoryProductsBySkuStmt->fetchAll(\PDO::FETCH_ASSOC) as $categoryProduct) {
            $categoryProducts[$categoryProduct[MemberNames::CATEGORY_ID]] = $categoryProduct;
        }

        // return the category product relations
        return $categoryProducts;
    }