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

        $cst = Schema::getComboSetsTable();
        $csgt = Schema::getComboSetGroupsTable();
        $csgit = Schema::getComboSetGroupItemsTable();
        $res = $wpdb->get_var(
            $wpdb->prepare(
                "SELECT COUNT(cs.ID)
                FROM {$cst} cs 
                JOIN {$csgt} cg ON cg.combo_set_id = cs.ID
                JOIN {$csgit} gi ON gi.group_id = cg.ID
                WHERE gi.welitem_sku_meta_id = %d",
                (int)$skuMetaId
            )
        );
        if ($res === null) {
            return Master::getErrorStore()->getErrorResponse(ErrorStore::INTERNAL_SERVER_ERROR);
        }

        return (bool)(int)$res;
    }