On Sat, Oct 12, 2019 at 04:39:56PM +0200, Ivan Voras wrote: > With seqscan disabled, I get this plan on 9.6: > Bitmap Heap Scan on friend (cost=8.42..19.01 rows=14 width=8) ... > I expected to get an index-only scan in this situation, as that would be a > very common query. Is there a way to actually make this sort of query > resolvable with an index-only scan? Maybe a different table structure would > help?
It would have to scan the entire index to find the cases where user2_id=42 but user1_id is not constrained. Technically User1_id would be constrained to be less than 42, but I don't think the planner will take that into account.
