updating dup row

Hi all,

how can I update a row with newest id from another table if it exists
somewhere else?

Example:

*table test1*

- id (primary key)
- id_user_bill
- clientid

*table test2*

- item_id
- userid (there are duplicated rows here)
- clientid
- id (primary key)

-- finding the dup records
INSERT INTO test2_results

SELECT

item_id,

userid

count(*) as dup_count,

MAX(id) as recent_id

FROM

test2

GROUP BY

item_id,

userid

HAVING COUNT(*) > 1;

if test1.id_user_bill = test2.id, then
update test1.id_user_bill with test2_results.recent_id

I'm using PG 9.2

Thanks!
Patrick.