Horton

Re: Wrong results with grouping sets

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Alena Rybakina <lena.ribackina@yandex.ru>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2023-11-17T03:25:11Z
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. Remove the RTE_GROUP RTE if we drop the groupClause

  2. Mark expressions nullable by grouping sets

  3. Introduce an RTE for the grouping step

On Thu, Nov 16, 2023 at 11:25 PM Alena Rybakina <lena.ribackina@yandex.ru>
wrote:

> I noticed that this query worked correctly in the main branch with the
> inequality operator:
>
> postgres=# select distinct on (a, b) a, b from (values (3, 1), (2, 2)) as
> t (a, b) where a > b group by grouping sets((a, b), (a)); a | b ---+--- 3 |
> 1 3 | (2 rows)
>
> So, I think you are right)
>

Thanks for taking an interest in this patch and verifying it.


> I looked at your patch and noticed a few things:
>
> 1. I think you should add a test with the cube operator, because I noticed
> that the order of the query in the result has also changed:
>

Hmm, I'm not sure if that's necessary.  The wrong result order you saw
here is caused by the same reason explained above: the planner fails to
realize that Var 'a' and 'b' are nullable by the grouping sets, making
them no longer always equal to each other.  This issue should have been
covered in the tests added by v1 patch.

Thanks
Richard