public function groupBy(string $sql, array $params = []) : self
    {
        $this->qiterator = null;
        $this->group = [ $sql, $params ];
        return $this;
    }
public function groupBy(string $sql, array $params = []) : self
    {
        $this->qiterator = null;
        $this->group = [ $sql, $params ];
        return $this;
    }
public function groupBy ( string $ sql , array $ params = [ ] ) : self { $ this -> qiterator = null ; $ this -> group = [ $ sql , $ params ] ; return $ this ; }
Apply advanced grouping
@param  string $sql    SQL statement to use in the GROUP BY clause
@param  array  $params optional params for the statement (defaults to an empty array)
@return $this
Apply advanced grouping