pgsql: Remove quals made redundant by reducing outer joins to antijoins

Remove quals made redundant by reducing outer joins to antijoins

When reduce_outer_joins reduces an outer join to an antijoin, any IS
NULL qual on a Var from the antijoin's nullable side is necessarily
true. Previously, such quals were discarded later in
distribute_qual_to_rels, mainly to avoid bogus selectivity estimates.
But that discard was incomplete: the qual remained in the jointree,
while its Vars were not counted in attr_needed. Since commit
2ebf25e7d, join removal edits the jointree and expects it to contain
no other references to a removed rel, so it could remove a rel that
such a discarded qual still references, and then trip an assertion on
the qual's stale Var.

To fix, move this processing to an earlier phase: such quals are now
removed from the jointree by reduce_outer_joins itself. This way
later phases see a consistent query tree, and
check_redundant_nullability_qual is no longer needed, so remove it.

Back-patch to v16, as with commit 2ebf25e7d.

Reported-by: Tender Wang <tndrwang(at)gmail(dot)com>
Author: Richard Guo <guofenglinux(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CAHewXNk8b0TsSy4dL=CO7FXL2W3WBm0BcdP-zwNJePa-Qj4HzA@mail.gmail.com
Backpatch-through: 16

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/763d563eaec82528fdd49c07830a2dae00567778

Modified Files
--------------
src/backend/optimizer/plan/initsplan.c | 61 ---------------------
src/backend/optimizer/prep/prepjointree.c | 89 ++++++++++++++++++++++++++++---
src/backend/optimizer/util/clauses.c | 11 ++--
src/test/regress/expected/join.out | 36 +++++++++++++
src/test/regress/sql/join.sql | 18 +++++++
5 files changed, 143 insertions(+), 72 deletions(-)