A subselect can only return 1 field. Your example should be rewritten

SELECT fkood, amnr
FROM koosseis k
WHERE not exists
(select 1 from isik i where i.fkood=k.fkood and i.amnr=k.amnr)

Set

--- In firebird-support@yahoogroups.com, Raigo wrote:
> How is made subselect query with more than one fields?
> For example:
>
> SELECT fkood, amnr
> FROM koosseis
> WHERE (fkood,amnr) NOT IN (SELECT fkood,amnr FROM isik)
>
> gives me error "Token unknown line 3 char 13".