public function update($sqlQuery = false)
    {
        $field = func_get_args();
        if(func_num_args() == 0) {
            echo 'no data to save'; //no argument
            exit;
        }
        elseif(func_num_args() == 1) {
            if(is_array($field[0])) {
                $data = $field[0]; //single array with all data
            }
            else {
                $data = $field[0]; //sql fraction
            }
        }
        else {
            echo 'invalid data';
            exit;
        }
        $sql = $this->buildQuery('update', $data);
        if($sqlQuery === true) {
            return $this->getQuery();
        }
        $result = $this->executeQuery($sql);
        return $result;
    }