Darek,

I don't think it should a problem. Here is a ddl that works:

create table my_table (
   id char(32) not null primary key,
   num integer not null,
   code varchar(2) not null,
   name varchar(60) not null,
   gen generated always as (id concat char(num) concat code)
);

Probably you should modify the code to remove white characters from the
generated value (I suggest to write SQL function to do this).

I think I know what your problem is. If you have data in your table,
you cannot just alter the table to add a generated column. Here is what
you should do:

set integrity for my_table off;
alter table my_table
 add column  gen generated always as (id concat char(num) concat code)
;
set integrity for my_table immediate checked force generated;

One important remark. If your my_table is in reference with other
tables (primary, foreign  keys) the first statement wil also move the
tables into "integrity off" state. So, in the last statement you must
put all the table names, and (this is important) as a one SQL
instruction, eg.

set integrity for my_table, fk_my_table, fk2_my table immediate checked
force generated;

Radosnych Swiat, Alleluja

-- Artur Wronski

Generated columns are a performance feature just like MQTs and
replicated tables.
There are two main reasons for them:
1. Improve performance of where clauses with expressions in them.
2. Improve performance of queries with expensive expressions.

Functionally dependent columns are discouraged because they can become
inconsistent. Generated columns are designed from teh ground up to
remain consistent.
So, all you pay is storage.

So, while they may not belong into the first schema design they have
their rightful place in reality.

Cheers
Serge