PostgreSQL: system UID

[Plakhotnik]

I have two table

user: only one field - user_id (UNN) (PK)

and

reffer: two field - reffer_refid (NN) (PFK)
- reffer_userid (NN) (PFK)

for both last field primary foreign key field from first table.

I can't change database structure, but need unique field from last table.
I heard about system uin in all postgres table.

How I can get it?

Please help!

[ultraslacker]

If uniqueness is what you want, why not just use serial datatype?

[Sxooter]

You can get a unique name for a field like so:

select t1.f1 as fielda, t2.f1 as fieldb from table1 t1 join table2 t2 on (t1.k1=t2.k1);