Horton

Re: Inconsistent Behavior of GROUP BY ROLLUP in v17 vs master

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: 邱宇航 <iamqyh@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2025-09-23T07:38:14Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix test case from 40c242830

  2. Fix pushdown of degenerate HAVING clauses

  3. Allow pushdown of HAVING clauses with grouping sets

  4. Mark expressions nullable by grouping sets

On Tue, 23 Sept 2025 at 15:49, 邱宇航 <iamqyh@gmail.com> wrote:
> I've noticed that two GROUP BY ROLLUP queries behave differently in v17
> compared to master and REL_18_STABLE. The issue can be reproduced by
> following SQL:
>
> After some git bisect work, I traced the root cause:
> - The first issue was introduced by commit f5050f79 (Mark expressions
> nullable by grouping sets).
> - The second issue stems from commit 67a54b9e (Allow pushdown of HAVING
> clauses with grouping sets).

If you check the release notes and the commit message for f5050f795
you'll see that it does mention that wrong results could be returned.

What wasn't mentioned was that this wasn't fixed in prior versions.
The reason being is that the fix required changing the query tree
representation, which we can't change in the back branches due to
incompatibility with stored rules in existing databases. So, a change
in query results for certain queries here is expected.

David