pgsql: Fix Memoize to work with partitionwise joining.

Fix Memoize to work with partitionwise joining.

A couple of places weren't up to speed for this.  By sheer good
luck, we didn't fail but just selected a non-memoized join plan,
at least in the test case we have.  Nonetheless, it's a bug,
and I'm not quite sure that it couldn't have worse consequences
in other examples.  So back-patch to v14 where Memoize came in.

Richard Guo

Discussion: https://postgr.es/m/CAMbWs48GkNom272sfp0-WeD6_0HSR19BJ4H1c9ZKSfbVnJsvRg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d69d01ba9d8d774487032459ebb83d2086715f01

Modified Files
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src/backend/optimizer/path/joinpath.c |  3 ++-
src/backend/optimizer/util/pathnode.c |  1 +
src/include/nodes/pathnodes.h         |  4 ++--
src/test/regress/expected/memoize.out | 39 +++++++++++++++++++++++++++++++++++
src/test/regress/sql/memoize.sql      | 19 +++++++++++++++++
5 files changed, 63 insertions(+), 3 deletions(-)