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base repository: postgresql-cfbot/postgresql
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  • 2 commits
  • 3 files changed
  • 2 contributors

Commits on Dec 5, 2025

  1. Fix distinctness check for queries with grouping sets 

    query_is_distinct_for() is intended to determine whether a query never
returns duplicates of the specified columns.  For queries using
grouping sets, if there are no grouping expressions, the query may
contain one or more empty grouping sets.  The goal is to detect
whether there is exactly one empty grouping set, in which case the
query would return a single row and thus be distinct.

The previous logic in query_is_distinct_for() was incomplete because
the check was insufficiently thorough and could return false when it
could have returned true.  It failed to consider cases where the
DISTINCT clause is used on the GROUP BY, in which case duplicate empty
grouping sets are removed, leaving only one.  It also did not
correctly handle all possible structures of GroupingSet nodes that
represent a single empty grouping set.

To fix, add a check for the groupDistinct flag, and expand the query's
groupingSets tree into a flat list, then verify that the expanded list
contains only one element.

No backpatch as this could result in plan changes.

Author: Richard Guo <guofenglinux@gmail.com>
Discussion: https://postgr.es/m/CAMbWs480Z04NtP8-O55uROq2Zego309+h3hhaZhz6ztmgWLEBw@mail.gmail.com
    @guofengrichard
    guofengrichard authored and Commitfest Bot committed Dec 5, 2025
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  2. [CF 6189] v3 - Fix distinctness check for queries with grouping sets 

    This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/6189

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CAMbWs49HrvGcVqX7YBFkU0o9ev_-9Xq=PySUfv-4winKye_6fg@mail.gmail.com
Author(s): Richard Guo
    Commitfest Bot committed Dec 5, 2025
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