selecteer max en min waarden elke x aantal rijen-postgresql

U kunt vaste aantallen rijen samenvoegen met row_number() en rekenen:

select min(date),
       (array_agg(bid order by seqnum asc))[1] as open,
       (array_agg(bid order by seqnum desc))[1] as close,
       min(bid) as min_bid, max(bid) as max_bid
from (select t.*, row_number() over (order by date) as seqnum
      from ticks t
     ) t
group by floor((seqnum - 1) / 500);

Dit gebruikt "hack" om de open . te krijgen en close -- door arrays te gebruiken.