protected function buildInsertSet(
        /*# string */ $prefix,
        array $settings
    )/*# : string */ {
        if (empty($this->set_data)) {
            return '';
        }

        $cols = [];
        foreach (array_keys($this->set_col) as $col) {
            $cols[] = $this->quote($col, $settings);
        }
        return $settings['seperator'] . '(' . join(', ', $cols) . ')';
    }