protected function translateExists()
    {
        $translator = new static;

        // translate the subselect
        list($subQuery, $subQueryParameters) = $translator->translate($this->attr('select'));

        // merge the parameters
        foreach($subQueryParameters as $parameter)
        {
            $this->addParameter($parameter);
        }

        return 'select exists(' . $subQuery .') as `exists`';
    }