public static function renderValue(SQL\Set $item)
    {
        $value = $item->getValue();
        $content = $item->getContent();

        if ($value instanceof SQL\SQL) {
            return $value->getContent();
        } elseif ($value instanceof Query\Select) {
            return Compiler::braced(Select::render($value));
        } elseif ($item instanceof SQL\SetMultiple and is_string($content)) {
            return self::renderMultiple($value, $content, $item->getKey());
        } else {
            return '?';
        }
    }