protected static function isExpression($field)
    {
        $alias = explode(' as ', $field);
        $field = trim($alias[0]);
        if (preg_match('/\S+\(\S*\)/', $field) === 1) {
            if (isset($alias[1])) {
                return trim($alias[1]);
            }

            return true;
        }

        return false;
    }