Re: HashJoin w/option to unique-ify inner rel

Robert Haas <robertmhaas@gmail.com> writes:
> Upon further review, it appears that a big part of this problem is
> that cost_hashjoin() doesn't understand that it needs cost semi-joins
> differently from inner or left joins.

Yeah, I have a note to look into that before 8.4 final.  The same is
true for nestloops: stopping after hitting one match to the current
outer can make a big difference, and that's not reflected in costsize.c
yet.  I'm not sure whether cost_mergejoin needs to care.
        regards, tom lane