[URGENT] How to generata a unique string id

From: "Manuel Dur�n Aguete" <mdaguete@alsernet.es>

I need to generate a unique four letters string (p.e
AAAA,AAAB) for any tuple I insert into a table, any idea ? How can I do
this ?

Create a sequence foo_seq and then set your field

create table example (
id default myfunc(nextval(foo_seq)),
a text,
b int4
);

Define myfunc to convert the integer into a character string (take the value
mod 26, append to string, divide value by 26, repeat)

- Richard Huxton