protected function expression(string $identifier): string
    {
        return preg_replace_callback('/([a-z][0-9_a-z\.]*\(?)/i', function ($match) {
            $identifier = $match[1];

            //Function name
            if ($this->hasExpressions($identifier)) {
                return $identifier;
            }

            return $this->quote($identifier);
        }, $identifier);
    }