How to look at a pet focus, see what pets are associated with it
 

I have been told that the way pet focii work is that it summons an alternate pet if the pet focus is worn at the time, but no idea how to look for which focii are pet related, let alone how to join tables to see what pets are connected.

Basically I'm looking to understand how this works better, and what type of query I should be running to get a good list of what is going on. Any help greatly appreciated.