Try this....
CREATE SEQUENCE just_a_seq;
Select nextval('just_a_seq') as row_no, * from pg_tables ;
drop SEQUENCE just_a_seq;
>
> row_no | column1 | column2 | ...
> -------+---------+---------+ ...
> 1 | datum11 | datum12 | ...
> 2 | datum21 | datum22 | ...
> ... | ... | ... | ...
>
> I didn't find anything in the docs.
>
> TIA, Zoltan
>