Thanks!
I'll investigate (explain) performance for both versions.
> with QRY as (select C1.country, C1.state, sum(C1.population) > from places C1 > group by 1, 2 > order by 3 DESC > limit 10) > > select * from QRY > union > select 'others' as "country", '' as "state", sum(population) > from places > where not exists (select 1 from QRY where country = QRY.country and state > = QRY.state) >