Re: Removing unneeded self joins

Hi, Andrei!

Thank you for your feedback.

On Mon, Feb 24, 2025 at 12:12 AM Andrei Lepikhov <lepihov(at)gmail(dot)com> wrote:
> On 23/2/2025 22:15, Alexander Korotkov wrote:
> > There is my attempt to implement this approach. Getting rid of local
> > variable (and computation of the same value other way) required to
> > change arguments of remove_rel_from_eclass() as well. I'm going to
> > further polish this tomorrow.
> I passed through the patch. It works correctly.
>
> Multiple ifs in a single routine is not ideal.

I would say there is a brachcing anyway. Even if it is inside
adjust_relid_set(). Patch makes it more explicit. Ideal or not, I
don't think it gets worse.

> I have thought about it
> already, and it seems the remove_rel_from_query needs refactoring: when
> I first reused it for self-join removal, we didn't have the 'ojrelid'
> machinery, and it was implemented smoothly.
> Right now, this code contains multiple places where we need to remove
> the outer join relid and separating the removal code for the baserel and
> outer join may simplify the logic and make it safer.
> But the way to do it is not apparent now. May be if we implement a new
> technique of query tree reduction, the approach will become more evident.

Could you, please, elaborate more on what you mean by "new technique
of query tree reduction"?

------
Regards,
Alexander Korotkov
Supabase