I have the following schema:

table keyvaluepairs(k integer, v integer)
index keyvalue_idx on keyvaluepairs(k)

table validkeys(k integer)

For example, when I do a

select v from keyvaluepairs where k = 1

it uses the index keyvalue_idx and is pretty fast.

But when I do a

select v from keyvaluepairs where k in (select k from validkeys)

it stops using the index and does a full scan on keyvaluepairs and is
slow.

I realize I could use a join instead of the nested select which would
fix the problem but I need to use this SQL to create a view and using
a join would prevent the view from being updateable.

I tried to specify the plan

select v from keyvaluepairs
where k in (select k from validkeys)
PLAN (keyvaluepairs INDEX (keyvalue_idx))

but it said "unable to use index "

Any clues as to how to fix this performance issue ?

Thanks.