Re: When can joins be avoided?

Stefan Fehrenbach <stefan.fehrenbach@gmail.com> writes:
> I'm interested in the rules that Postgres uses to avoid joins. Are
> these documented somewhere? If I had to look at the source code, where
> would I start?

src/backend/optimizer/plan/analyzejoins.c

> They don't seem to match my intuition about which joins
> could be avoided.

I believe only left joins to single tables can be elided ATM.
It's too hard to prove uniqueness of the join key in more-
complicated cases.

            regards, tom lane