select array aggregates

query.sql

-- This will give us a table that has a row for each resource but includes all of the events related to the 
-- resource on the row. Calling array_agg will load all of the data in memory which means that I can do math 
-- on the set really quickly. Also, callers of this query will be able to get all of the data for the invoice 
-- in one shot.

create view invoice as
select
 a.resource_id,
 sum(a.qty) as qty,
 array_agg(hstore(a.*)) as events_collection
from events
group by a.resource_id;

http://www.postgresql.org/docs/9.1/static/functions-aggregate.html

Oh, and you can return an array of hstores :)