code: public function addSelect(string $expression, ...$args): self
  	{
  		if (!is_string($expression)) {
  			throw new InvalidArgumentException('Select expression has to be a string.');
  		}
  		$this->dirty();
  		$this->select[] = $expression;
  		$this->pushArgs('select', $args);
  		return $this;
  	}
docs: Adds expression to SELECT clause.