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

On Tue, Sep 23, 2025 at 07:38:14PM +1200, David Rowley wrote:
> 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.

Uh, by design, items mentioned in the major release notes have _not_
been fixed in previous minor versions.  Not sure if we can make that
clearer to users.  I did write a blog about this:

    https://momjian.us/main/blogs/pgblog/2022.html#June_13_2022

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Do not let urgent matters crowd out time for investment in the future.