Hi Joost,
Try joining and comparing the order table with/to an aggregated orderline
table, something like this:
select order_id, order_price, sum_price, order_price - sum_price as diff
from order, (select parent_order_id, sum(orderline_price) as sum_price
from orderline group by parent_order_id) as foo
where order_id = parent_order_id
and order_price != sum_price
This should prove to be as efficient as it gets ;)
--
Best,
Frank.