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Tom Lane e6d8639cf2 Prevent join removal from removing the query's result relation. 
This was not something that required consideration before MERGE
was invented; but MERGE builds a join tree that left-joins to the
result relation, meaning that remove_useless_joins will consider
removing it.  That should generally be stopped by the query's use
of output variables from the result relation.  However, if the
result relation is inherited (e.g. a partitioned table) then
we don't add any row identity variables to the query until
expand_inherited_rtentry, which happens after join removal.

This was exposed as of commit 3c569049b, which made it possible
to deduce that a partitioned table could contain at most one row
matching a join key, enabling removal of the not-yet-expanded
result relation.  Ooops.

To fix, let's just teach join_is_removable that the query result
rel is never removable.  It's a cheap enough test in any case,
and it'll save some cycles that we'd otherwise expend in proving
that it's not removable, even in the cases we got right.

Back-patch to v15 where MERGE was added.  Although I think the
case cannot be reached in v15, this seems like cheap insurance.

Per investigation of a report from Alexander Lakhin.

Discussion: https://postgr.es/m/36bee393-b351-16ac-93b2-d46d83637e45@gmail.com
 		2023-02-20 15:18:32 -05:00
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contrib Limit memory usage of pg_walinspect functions. 2023-02-20 11:29:31 -08:00
doc Stop recommending auto-download of DTD files, and indeed disable it. 2023-02-08 17:15:23 -05:00
src Prevent join removal from removing the query's result relation. 2023-02-20 15:18:32 -05:00
.cirrus.yml ci: Use windows VMs instead of windows containers 2023-02-02 21:31:48 -08:00
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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/.