Why USE KEYS error shown when using DB name

SQL++
,
5

When I remove the constants and use a subquery like below, it times out.

SELECT v.type d, ARRAY_AGG({"v":v})[1:5] l                                                                                            
FROM `my-db` v
WHERE v.type IN (select distinct type from `my-db`)
GROUP BY v.type
;

I am guessing its an indexing issue? Have a new post on this here.