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Richard Guo cf74558feb Reduce LEFT JOIN to ANTI JOIN using NOT NULL constraints 
For a LEFT JOIN, if any var from the right-hand side (RHS) is forced
to null by upper-level quals but is known to be non-null for any
matching row, the only way the upper quals can be satisfied is if the
join fails to match, producing a null-extended row.  Thus, we can
treat this left join as an anti-join.

Previously, this transformation was limited to cases where the join's
own quals were strict for the var forced to null by upper qual levels.
This patch extends the logic to check table constraints, leveraging
the NOT NULL attribute information already available thanks to the
infrastructure introduced by e2debb643.  If a forced-null var belongs
to the RHS and is defined as NOT NULL in the schema (and is not
nullable due to lower-level outer joins), we know that the left join
can be reduced to an anti-join.

Note that to ensure the var is not nullable by any lower-level outer
joins within the current subtree, we collect the relids of base rels
that are nullable within each subtree during the first pass of the
reduce-outer-joins process.  This allows us to verify in the second
pass that a NOT NULL var is indeed safe to treat as non-nullable.

Based on a proposal by Nicolas Adenis-Lamarre, but this is not the
original patch.

Suggested-by: Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com>
Author: Tender Wang <tndrwang@gmail.com>
Co-authored-by: Richard Guo <guofenglinux@gmail.com>
Discussion: https://postgr.es/m/CACPGbctKMDP50PpRH09in+oWbHtZdahWSroRstLPOoSDKwoFsw@mail.gmail.com
2026-02-12 15:30:13 +09:00
.github Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md. 2024-07-02 13:03:58 -05:00
config Revert "Change copyObject() to use typeof_unqual" 2026-02-07 10:08:38 +01:00
contrib Further stabilize a postgres_fdw test case. 2026-02-11 11:03:17 -05:00
doc Add password expiration warnings. 2026-02-11 10:36:15 -06:00
src Reduce LEFT JOIN to ANTI JOIN using NOT NULL constraints 2026-02-12 15:30:13 +09:00
.cirrus.star ci: Simplify ci-os-only handling 2025-08-14 12:09:34 -04:00
.cirrus.tasks.yml ci: Configure g++ with 32-bit for 32-bit build 2026-01-09 08:58:50 +01:00
.cirrus.yml ci: Per-repo configuration for manually trigger tasks 2025-08-14 11:54:03 -04:00
.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 a couple of recent commits to .git-blame-ignore-revs. 2026-01-28 15:56:48 -06:00
.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 Revert "Change copyObject() to use typeof_unqual" 2026-02-07 10:08:38 +01:00
configure.ac Revert "Change copyObject() to use typeof_unqual" 2026-02-07 10:08:38 +01:00
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 Remove AIX support 2024-02-28 15:17:23 +04:00
meson.build meson: host_system value for Solaris is 'sunos' not 'solaris'. 2026-02-07 20:05:52 -05:00
meson_options.txt Update copyright for 2026 2026-01-01 13:24:10 -05:00
README.md Revise the style of a paragraph in README.md. 2024-03-21 10:16:41 -05:00

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/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/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/.