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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
..
backend Prevent join removal from removing the query's result relation. 2023-02-20 15:18:32 -05:00
bin Translation updates 2023-02-06 12:15:49 +01:00
common Change some errdetail() to errdetail_internal() 2022-09-28 17:14:53 +02:00
fe_utils Use correct connection for cancellation in frontend's parallel slots 2022-08-27 15:22:07 +09:00
include Fix handling of SCRAM-SHA-256's channel binding with RSA-PSS certificates 2023-02-15 10:12:31 +09:00
interfaces Fix handling of SCRAM-SHA-256's channel binding with RSA-PSS certificates 2023-02-15 10:12:31 +09:00
makefiles Refactor DLSUFFIX handling 2022-03-25 08:56:02 +01:00
pl perl: Hide warnings inside perl.h when using gcc compatible compiler 2023-01-02 15:49:33 -08:00
port Re-allow building on Microsoft Visual Studio 2013. 2022-11-10 10:23:49 -05:00
template On NetBSD, force dynamic symbol resolution at postmaster start. 2022-08-30 17:28:55 -04:00
test Prevent join removal from removing the query's result relation. 2023-02-20 15:18:32 -05:00
timezone Update time zone data files to tzdata release 2022g. 2023-01-31 17:37:06 -05:00
tools Fix handling of SCRAM-SHA-256's channel binding with RSA-PSS certificates 2023-02-15 10:12:31 +09:00
tutorial Doc: sync src/tutorial/basics.source with SGML documentation. 2022-11-19 13:09:14 -05:00
.gitignore
DEVELOPERS
Makefile Remove the option to build thread_test.c outside configure. 2020-10-21 12:08:48 -04:00
Makefile.global.in Prevent port collisions between concurrent TAP tests 2022-11-22 10:51:13 -05:00
Makefile.shlib AIX: Fix missing libpq symbols by respecting SHLIB_EXPORTS. 2021-09-06 11:27:59 -07:00
nls-global.mk Improve frontend error logging style. 2022-04-08 14:55:14 -04:00