problem with subqueries

Hi

Any help appreciated - I have spent 2 days trying to get this query to
work!

I have an orders database and a customer database. 

The orders database has a date field for each order.  

Because I want to obtain a monthly breakdown, I created a view called
monthcustomer as this select:
select orders.ord_date, customer.cname,date_part('month',orders.ord_date) AS "month", date_part('year',orders.ord_date)
AS"year", orders.number_of_items;
 

Each month will have multiple numbers of items, so to get a monthly
breakdown I tried this:
select distinct year,month, (select sum(monthcustomer.number_of_items) from monthcustomer where
monthcustomer.year=m.yearand  monthcustomer.month=m.month) as NumPotsfrom monthcustomer m;
 

This goes off and never comes back - CPU is hitting the top of the
chart! I have to ^C to interrupt it, as it runs for ages (I've left
this run for 10-20 minutes and it is still running).

I have indexes on the columns involved from the original tables.

Any help appreciated.

Pete

PS: Using pgsql 7.2-70 from Suse distribution.