Re: Clause accidentally pushed down ( Possible bug in Making Vars outer-join aware)

Agreed that we need to actually change the individual Vars/PHVs because
I find that with my patch it's not easy to fake the quals deduced from
ECs as there is no 'current JoinTreeItem' there.  I'm not sure that
there is nullingrels mis-match issue though, because when forming an
outer join's target list we've ensured that the output Vars are always
marked according to the syntactic tree structure.

 

So IIUC the idea is that if we are given the first form of identity 3,
we update all upper C Vars so that they are marked with both OJ relids.
It seems that this may have nullingrels mis-match issue because of how
we form outer join's target list.  Consider

  A leftjoin B on (Pab) leftjoin C on (Pbc) inner join D on (Pcd)

At first C Vars in Pcd is marked only with B/C join.  Then we detect
that A/B join commutes with B/C join so we update C Vars in Pcd as being
marked with B/C join and A/B join.  However C Vars in the target list of
joinrel A/B/C would be marked only with B/C join as that is consistent
with the syntactic tree structure.  So when we process the joinqual Pcd
for C/D join in setrefs.c, I think we would have assertion failures
about nullingrels mismatch.  (This is just my imagination.  I haven't
implemented the codes to verify it.)

Thanks
Richard