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David Rowley 4297a35196 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 23:47:37 +13:00
config Don't put library-supplied -L/-I switches before user-supplied ones. 2025-07-29 15:17:41 -04:00
contrib Fix bogus ctid requirement for dummy-root partitioned targets 2026-01-23 10:23:18 +09:00
doc doc: Mention pg_get_partition_constraintdef() 2026-01-22 16:35:50 +09:00
src Fix possible issue of a WindowFunc being in the wrong WindowClause 2026-01-26 23:47:37 +13:00
.abi-compliance-history Update .abi-compliance-history for PrepareToInvalidateCacheTuple(). 2025-12-17 09:48:56 -08:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:03:27 -04:00
.cirrus.tasks.yml Fix typo 2026-01-07 15:49:00 +01:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:33:50 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add .editorconfig 2019-12-18 09:13:13 +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 10:31:52 +02:00
.gitignore Update top-level .gitignore. 2022-12-04 15:23:00 -05:00
aclocal.m4 autoconf: Move export_dynamic determination to configure 2022-12-06 18:55:28 -08:00
configure Stamp 16.11. 2025-11-10 16:55:22 -05:00
configure.ac Stamp 16.11. 2025-11-10 16:55:22 -05:00
COPYRIGHT Update copyright for 2026 2026-01-01 13:24:10 -05:00
GNUmakefile.in Integrate pg_bsd_indent into our build/test infrastructure. 2023-02-12 12:22:21 -05:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Dynamically find correct installation docs in Makefile. 2022-01-19 14:48:25 +01:00
meson.build Add check for large files in meson.build 2025-11-12 09:02:35 +09:00
meson_options.txt meson: Attach colon to keyword argument 2023-06-29 12:53:41 +02:00
README Canonicalize some URLs 2020-02-10 20:47:50 +01:00
README.git Canonicalize some URLs 2020-02-10 20:47:50 +01:00

README 

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.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download/

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

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