My first PL/pgSQL function

I am by no means an expert in PL/SQL but your function seems ok to me;

your currcal is fine (if you used nextval as someone suggested, you'd get
the next value, which is not what you intend, creating user<->groups links.

That said, I ddo not know if doing and insert then asking for curval is
atomic or if you could get a wrong value if someone else creates a user at
theat moment;

To be on the safe side, I always use insert ... returning syntax this way I
know that I am getting the same value as the one inserted.

Just my 0.02EUR

Didier