function aggregation($function){
        $join  = $this->createJoins(implode(",", $this->conditions) . ",$function");
        $query = "SELECT $function FROM $this->table" . implode($join);
        if($this->where){
            $query .= " WHERE " . implode($this->where);
        }

        foreach($this->query($query, $this->parameters)->fetch() as $return){
            return $return;
        }
    }