IMHO you should use another table instead of an array.
Forget about reasonable speed when using IN sub-queries, you'll get a
sequential scan of the sub-query for every row in the master select. I've
heard the EXISTS operator provides far better performance.
In 7.1, there's a very nice solution: use the sub-query in the FROM clause
and make joins to it. Should be MUCH faster.
> But this causes an error because the array field just returns a string
> instead of seperated values. Is there a way to make arrays return sort
> of "real arrays" or something usable in a subselect in reasonable speed?