Simon Riggs <simon@2ndquadrant.com> writes:
> What I would add is that I've seen cases where the extra joins do NOT
> hurt performance, so the extra CPU used to remove the join hurts more
> than the benefit of removing it. Yes, we tried it.
Interesting. The concern I had was more about the cost imposed on every
query to detect self-joins and try to prove them useless, even in queries
where no benefit ensues. It's possible that we can get that down to the
point where it's negligible; but this says that even the successful-proof
case has to be very cheap.
regards, tom lane