Checking result of $db->query_write

[rudgej]

What is the recommended way of checking the outcome of a "$db->query_write"?

I want to either update a record with a defined id number, or insert a record if the id number doesn't exist. I thought that I would be able to do an update transaction first, check if there is an error, and only then do an insert transaction if needed.

All suggestions as to the best way to do this gratefully received.