Re: Making Vars outer-join aware

On Thu, Aug 25, 2022 at 5:18 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Richard Guo <guofenglinux(at)gmail(dot)com> writes:
> > Do we need to also
> > generate two SpecialJoinInfos for the B/C join in the first order, with
> > and without the A/B join in its min_lefthand?
>
> No, the SpecialJoinInfos would stay as they are now. It's already the
> case that the first join's min_righthand would contain only B, and
> the second one's min_righthand would contain only C.

I'm not sure if I understand it correctly. If we are given the first
order from the parser, the SpecialJoinInfo for the B/C join would have
min_lefthand as containing both B and the A/B join. And this
SpecialJoinInfo would make the B/C join be invalid, which is not what we
want. Currently the patch resolves this by explicitly running
remove_unneeded_nulling_relids, and the A/B join would be removed from
B/C join's min_lefthand, if Pbc is strict for B.

Do we still need this kind of fixup if we are to keep just one form of
SpecialJoinInfo and two forms of RestrictInfos?

Thanks
Richard