src/RocknRoot/StrayFw/Database/Postgres/Query/Select.php
public function groupBy($groupBy)
    {
        if (is_array($groupBy) === true) {
            $this->groupBy = implode(', ', $groupBy);
        } else {
            $this->groupBy = $groupBy;
        }

        return $this;
    }
public function groupBy($groupBy)
    {
        if (is_array($groupBy) === true) {
            $this->groupBy = implode(', ', $groupBy);
        } else {
            $this->groupBy = $groupBy;
        }

        return $this;
    }
Set group by clause.

@param  array|string $groupBy group by clause
@return Select       this