declare global temporary table session.#tmp as (
select *, rownumber() over() rn 
from ...
) definition only with replace on commit preserve rows not logged;

insert into session.#tmp 
select *, rownumber() over() rn 
from ...;

select * 
from syscat.columns 
where tabschema='...' and tabname='...'

declare global temporary table session.#tmp(
id int generated always as identity, v varchar( 10 )
) with replace on commit preserve rows not logged;

select id, v
from new table(
insert into session.#tmp (v) 
values ('a'), ('b'), ('c')
) t;