protected function _extractColumnsFromSelectQuery()
    {
        $_query = $this->getSelectQuery();
        $_matches = array();

        $_pattern = '#.*(SELECT)(.*)(FROM|LEFT|JOIN)#ims';
        preg_match($_pattern, $_query, $_matches);

        $_columnsList = explode(',', $_matches[2]);

        array_walk($_columnsList, function (&$value, $index) {
            $value = trim($value);
        });

        return $_columnsList;
    }