id from a field

I there!! I'm having a problem. I know that it's possible to know the exact
ID of a table or a column using OIDs but, is it possible to know the ID from
a field?. for example I have a table named "identities" with 3 columns:
name,address and age and 3 users in that table:
richard | spain | 22
joe | france | 23
carol | italy | 24

for example, does the field "france" as a unique id that I could save and
get that info only with that id?

thanks a lot Luis