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David Rowley ccde5be686 Fix possible issue of a WindowFunc being in the wrong WindowClause 
ed1a88dda made it so WindowClauses can be merged when all window
functions belonging to the WindowClause can equally well use some
other WindowClause without any behavioral changes.  When that
optimization applies, the WindowFunc's "winref" gets adjusted to
reference the new WindowClause.

That commit does not work well with the deduplication logic in
find_window_functions(), which only added the WindowFunc to the list
when there wasn't already an identical WindowFunc in the list.  That
deduplication logic meant that the duplicate WindowFunc wouldn't get the
"winref" changed when optimize_window_clauses() was able to swap the
WindowFunc to another WindowClause.  This could lead to the following
error in the unlikely event that the deduplication code did something and
the duplicate WindowFunc happened to be moved into another WindowClause.

ERROR:  WindowFunc with winref 2 assigned to WindowAgg with winref 1

As it turns out, the deduplication logic in find_window_functions() is
pretty bogus.  It might have done something when added, as that code
predates b8d7f053c, which changed how projections work.  As it turns
out, at least now we *will* evaluate the duplicate WindowFuncs.  All
that the deduplication code seems to do today is assist in
underestimating the WindowAggPath costs due to not counting the
evaluation costs of duplicate WindowFuncs.

Ideally the fix would be to remove the deduplication code, but that
could result in changes to the plan costs, as duplicate WindowFuncs
would then be costed.  Instead, let's play it safe and shift the
deduplication code so it runs after the other processing in
optimize_window_clauses().

Backpatch only as far as v16 as there doesn't seem to be any other harm
done by the WindowFunc deduplication code before then.  This issue was
fixed in master by 7027dd499.

Reported-by: Meng Zhang <mza117jc@gmail.com>
Author: Meng Zhang <mza117jc@gmail.com>
Author: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAErYLFAuxmW0UVdgrz7iiuNrxGQnFK_OP9hBD5CUzRgjrVrz=Q@mail.gmail.com
Backpatch-through: 16
2026-01-26 23:46:23 +13:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Don't put library-supplied -L/-I switches before user-supplied ones. 2025-07-29 15:17:40 -04:00
contrib Fix bogus ctid requirement for dummy-root partitioned targets 2026-01-23 10:23:26 +09:00
doc doc: Mention pg_get_partition_constraintdef() 2026-01-22 16:35:40 +09:00
src Fix possible issue of a WindowFunc being in the wrong WindowClause 2026-01-26 23:46:23 +13:00
.abi-compliance-history Update .abi-compliance-history for CacheInvalidateHeapTupleInplace(). 2025-12-16 10:01:28 -08:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:53 -04:00
.cirrus.tasks.yml Fix typo 2026-01-07 15:48:45 +01:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:33:44 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add script to keep .editorconfig in sync with .gitattributes 2025-02-01 10:09:45 +01:00
.git-blame-ignore-revs Add previous commit to .git-blame-ignore-revs. 2025-10-21 10:02:19 -05:00
.gitattributes Fix git whitespace warning 2025-08-15 10:32:22 +02:00
.gitignore Update top-level .gitignore. 2022-12-04 15:23:00 -05:00
.mailmap Add a Git .mailmap file 2024-11-05 13:56:02 +01:00
aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
configure Stamp 18.1. 2025-11-10 16:52:06 -05:00
configure.ac Stamp 18.1. 2025-11-10 16:52:06 -05:00
COPYRIGHT Update copyright for 2026 2026-01-01 13:24:10 -05:00
GNUmakefile.in Allow selecting the git revision to be packaged by "make dist". 2024-05-03 11:08:50 -04:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Adapt REL_18_STABLE to its new status as a stable branch 2025-06-29 23:00:00 -04:00
meson.build Fix macro name for io_uring_queue_init_mem check. 2025-12-31 11:18:17 -08:00
meson_options.txt Add support for basic NUMA awareness 2025-04-07 23:08:17 +02:00
README.md Adapt REL_18_STABLE to its new status as a stable branch 2025-06-29 23:00:00 -04:00

README.md

PostgreSQL Database Management System

This directory contains the source code distribution of the PostgreSQL database management system.

PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.

Copyright and license information can be found in the file COPYRIGHT.

General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/18/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/18/installation.html.

The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.