Nette\Database\Table\Selection::aggregation PHP Method

    public function aggregation($function)
    {
        $selection = $this->createSelectionInstance();
        $selection->getSqlBuilder()->importConditions($this->getSqlBuilder());
        $selection->select($function);
        foreach ($selection->fetch() as $val) {
            return $val;
        }
    }

 /**
  * Executes aggregation function.
  *
  * @param $function string select call in "FUNCTION(column)" format
  * @return string
  */
 public function aggregation($function)
 {
     return $this->selection->aggregation($function);
 }