Re: Allowing join removals for more join types

Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> TBH I think that trying to do anything at all for inner joins is probably
>> a bad idea.  The cases where the optimization could succeed are so narrow
>> that it's unlikely to be worth adding cycles to every query to check.

> I agree that we don't want to add too many cycles to trivial queries but
> I don't think it's at all fair to say that FK-check joins are a narrow
> use-case and avoiding that join could be a very nice win.

[ thinks for a bit... ]  OK, I'd been thinking that to avoid a join the
otherwise-unreferenced table would have to have a join column that is both
unique and the referencing side of an FK to the other table's join column.
But after consuming more caffeine I see I got that backwards and it would
need to be the *referenced* side of the FK, which is indeed a whole lot
more plausible case.
        regards, tom lane