Cover NEST query

SQL++
1

I have a query like

SELECT 
   a.id,
   ARRAY {b.foo} for bItem IN b END 
FROM bucket a
NEST bucket b ON a.id=b.id AND b.type='B'
WHERE a.type='A'

If I use JOIN instead of NEST the query used covering index , But in NEST it fetches b too
How can I change query or add index to cover NEST?

2

NEST query can’t be covered . if need covering use JOIN + GROUP BY+ARRAY_AGG()