sql code, when and where?

[kedikatt]

Newb question. Some info and concepts are just hard to find in search.

I wish to execute some sql ( or php code if someone would like to show it) to subtract an integer value that is entered in the record from a field in another table.
I can write the sql code to do the subtraction, but I do not have a clue how to implement it in Xataface. This is my first foray into this application.

If there is a basic example of triggering such things please point me there.

[kedikatt]

ADobkin replied to another question of mine which also helps a lot with this, with this documentation link.
http://www.xataface.com/documentation/tutorial/getting_started/delegate_classes

[ADobkin]

Also take a look at these two pages in the wiki:

http://xataface.com/wiki/Grafted_fields

http://xataface.com/wiki/fieldname__default

Alan