Ouzo\Db\ModelQueryBuilder::groupBy PHP Method

    public function groupBy($groupBy)
    {
        if ($this->_selectModel) {
            throw new DbException("Cannot use group by without specifying columns.\n" . "e.g. Model::select('column, count(*)')->groupBy('column')->fetchAll();");
        }
        $this->_query->groupBy = $groupBy;
        return $this;
    }