external table

I am currently writing my own database apps in foxpro/dos (since 1980).
pg seems to be a good way to move on, but I see a couple of problems.

All of the application programs seem to be c based. Learning c for
business apps is a problem.

Currently I use a lookup database for many kinds of applications that I
create for my company. It seems that the sql database arrangement is to
have 1 database with multiple related tables inside. I do not want to
have to keep current multiple look-up tables (cities, counties, police
depts, their phone numbers, etc.) in separate databases. Can I use, say
a database with billing tables (transacions, etc.) and refer to an
external lookup table? I might store a "G" in the city field, which
would refer to "San Francisco", etc.

tia,
John