public function addGroupBy($expression, ...$args): self
	{
		$this->dirty();
		$this->group[] = $expression;
		$this->pushArgs('group', $args);
		return $this;
	}
public function addGroupBy($expression, ...$args): self
	{
		$this->dirty();
		$this->group[] = $expression;
		$this->pushArgs('group', $args);
		return $this;
	}
Adds expression to GROUP BY clause.