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David Rowley fcd58c6d96 Fix COUNT's logic for window run condition support 
9d9c02ccd added code to allow the executor to stop early when processing
WindowAgg nodes where a monotonic window function starts producing
values that result in a pushed-down qual no longer matching, and will
never match again due to the window function's monotonic properties.

That commit requires a SupportRequestWFuncMonotonic to exist on the
window function and for it to detect when the function is monotonic.  For
COUNT(ANY) and COUNT(*), the support function failed to consider some
cases where the WindowClause used EXCLUDE to exclude certain rows from
being aggregated.  Some WindowClause definitions mean we aggregate rows
that come after the current row, and when processing those rows later,
if we EXCLUDE certain rows, the monotonic property can be broken.
Wrongly treating the COUNT(*) or COUNT(ANY) aggregate as monotonic could
lead to rows being filtered that should not be filtered from the result
set.

Another issue was that the support function for the COUNT aggregate
mistakenly thought that a WindowClause without an ORDER BY meant that
the results would be both monotonically increasing and decreasing, but
that's only true when in RANGE mode, where all rows are peers.

It is possible to support various cases that do have an EXCLUDE clause,
but getting the logic correct for the exact set of cases that are valid
is quite complex and would likely better be left for a future project.

Here, we mostly disable run condition pushdown when there is an EXCLUDE
clause unless the clause is for EXCLUDE CURRENT ROW, uses COUNT(*)
(rather than COUNT(ANY)), and the window aggregate has no FILTER clause.

Bug: #19533
Reported-by: Qifan Liu <imchifan@163.com>
Author: Chengpeng Yan <chengpeng_yan@outlook.com>
Author: David Rowley <dgrowleyml@gmail.com>
Reviewed-by: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Discussion: https://postgr.es/m/19533-413a1014e5d0e766@postgresql.org
Backpatch-through: 15
2026-07-07 23:58:29 +12:00
.github ci: Improve ccache handling 2026-06-08 15:26:47 -04:00
config Update config.guess and config.sub 2026-04-09 11:26:14 +02:00
contrib postgres_fdw: Report ANALYZE to pgstats after importing statistics. 2026-07-07 18:40:00 +09:00
doc Update GROUP BY ALL comments about window functions 2026-07-07 08:46:41 +02:00
src Fix COUNT's logic for window run condition support 2026-07-07 23:58:29 +12:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Update .editorconfig and .gitattributes for postgresql.conf.sample. 2025-11-18 10:28:36 -06:00
.git-blame-ignore-revs Add previous 2 commits to .git-blame-ignore-revs. 2026-06-29 15:33:52 -04:00
.gitattributes Update .editorconfig and .gitattributes for postgresql.conf.sample. 2025-11-18 10:28:36 -06:00
.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 19beta1. 2026-06-01 16:02:13 -04:00
configure.ac Stamp 19beta1. 2026-06-01 16:02:13 -04:00
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_19_STABLE to its new status as a stable branch 2026-06-29 16:39:23 -04:00
meson.build Stamp 19beta1. 2026-06-01 16:02:13 -04:00
meson_options.txt Revert "Add built-in fuzzing harnesses for security testing." 2026-04-10 09:53:58 -04:00
README.md Adapt REL_19_STABLE to its new status as a stable branch 2026-06-29 16:39:23 -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/19/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/19/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/.