How to call mysql stored functions

[eluser]Unknown[/eluser]
I find answer:

$sql = "select summ(?, ?) as result";
$query = $this->db->query($sql, array( 4, 5));
$result = $query->row()->result;

I want to write some php file that will be contain all my database function.
I dont know how it better to do. Please give me advice...

May be create helper, or my be use models...