public function groupBy($by, bool $escape = null)
	{
		is_bool($escape) || $escape = $this->db->protectIdentifiers;

		if (is_string($by))
		{
			$by = ($escape === true) ? explode(',', $by) : [$by];
		}

		foreach ($by as $val)
		{
			$val = trim($val);

			if ($val !== '')
			{
				$val = [
					'field'  => $val,
					'escape' => $escape,
				];

				$this->QBGroupBy[] = $val;
			}
		}

		return $this;
	}