public static function isComboSet($skuMetaId) {
        global $wpdb;

        $cst = Schema::getComboSetsTable();
        $exists = $wpdb->get_var(
            $wpdb->prepare(
                "SELECT COUNT(ID) FROM {$cst} WHERE sku_meta_id = %d",
                (int)$skuMetaId
            )
        );
        if ($exists === null) {
            return Master::getErrorStore()->getErrorResponse(ErrorStore::INTERNAL_SERVER_ERROR);
        }
        if ((bool)(int)$exists === true) {
            return true;
        }

        return false;
    }