yii\sphinx\QueryBuilder::buildGroupBy PHP Method

    public function buildGroupBy($columns, $limit)
    {
        if (empty($columns)) {
            return '';
        }
        if (is_string($limit) && ctype_digit($limit) || is_int($limit) && $limit >= 0) {
            $limitSql = ' ' . $limit;
        } else {
            $limitSql = '';
        }
        return 'GROUP' . $limitSql . ' BY ' . $this->buildColumns($columns);
    }