Re: Using bitmap index scans-more efficient

Kyle Bateman <kyle(at)actarg(dot)com> writes:
> But I'm assuming that using an interval-encoded project tree, I would
> have to do something like the following to get a progency group:

> select * from ledger l, proj p where p.proj_id = l.proj and p.left >
> 1234 and p.right < 2345;

btree has no idea about the constraint (that I imagine exists) that left
<= right. If you're just doing a simple index on (left, right) then the
above query requires scanning all index entries with left > 1234. It
would probably help to say

select * from ledger l, proj p where p.proj_id = l.proj and
p.left > 1234 and p.left < 2345 and p.right < 2345;

so that you can constrain the range of "left" values scanned.

regards, tom lane