sorry to post a new thread but something happened to the other one and i can't reply to it.
On DaPi's advice i used a query like this...
select id,
cast ( multiset( select user_id
from caw_tabsaccess
where caw_tabsaccess.tab_id = caw_tabs.id and caw_tabsaccess.user_id IS NOT null
group by user_id ) as ONEDNUMBERARRAY ) USER_ID
from caw_tabs;