Re: Index Skip Scan

On Wed, 11 Mar 2020 at 01:38, Dmitry Dolgov <9erthalion6@gmail.com> wrote:
>
> > >On Tue, Mar 10, 2020 at 09:29:32AM +1300, David Rowley wrote:
> > There's also some weird looking assumptions that an EquivalenceMember
> > can only be a Var in create_distinct_paths(). I think you're only
> > saved from crashing there because a ProjectionPath will be created
> > atop of the IndexPath to evaluate expressions, in which case you're
> > not seeing the IndexPath.  This results in the optimisation not
> > working in cases like:
>
> I've read it as "an assumption that an EquivalenceMember can only be a
> Var" results in "the optimisation not working in cases like this". But
> you've meant that ignoring a ProjectionPath with an IndexPath inside
> results in this optimisation not working, right? If so, then everything
> is clear, and my apologies, maybe I need to finally fix my sleep
> schedule :)

Yes, I was complaining that a ProjectionPath breaks the optimisation
and I don't believe there's any reason that it should.

I believe the way to make that work correctly requires paying
attention to the Path's uniquekeys rather than what type of path it
is.