From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Compare collations before merging UNION operations.
Date: Tue, 19 Nov 2024 23:26:42 +0000
Message-ID: <E1tDXcI-002cpF-CK@gemulon.postgresql.org> (raw)
Compare collations before merging UNION operations.
In the dim past we figured it was okay to ignore collations
when combining UNION set-operation nodes into a single N-way
UNION operation. I believe that was fine at the time, but
it stopped being fine when we added nondeterministic collations:
the semantics of distinct-ness are affected by those. v17 made
it even less fine by allowing per-child sorting operations to
be merged via MergeAppend, although I think we accidentally
avoided any live bug from that.
Add a check that collations match before deciding that two
UNION nodes are equivalent. I also failed to resist the
temptation to comment plan_union_children() a little better.
Back-patch to all supported branches (v13 now), since they
all have nondeterministic collations.
Discussion: https://postgr.es/m/3605568.1731970579@sss.pgh.pa.us
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/a43d7a8c7cce00e3fcf330e201a3a94f97097e64
Modified Files
--------------
src/backend/optimizer/prep/prepunion.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Compare collations before merging UNION operations.
In-Reply-To: <E1tDXcI-002cpF-CK@gemulon.postgresql.org>
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