code: public function groupBy($col, /*# bool */ $rawMode = false)
      {
          if (is_array($col)) {
              foreach ($col as $c) {
                  $this->groupBy($c, $rawMode);
              }
          } else {
              $this->clause_groupby[] = [
                  $rawMode ?: $this->isRaw($col), $col
              ];
          }
          return $this;
      }
docs: {@inheritDoc}