Re: Wrong results with grouping sets

On Mon, Sep 25, 2023 at 3:11 PM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:

> I think the root cause is that when we generate distinct_pathkeys, we
> failed to realize that Var 'b' might be nullable by the grouping sets,
> so it's no longer always equal to Var 'a'. It's not correct to deem
> that the PathKey for 'b' is redundant and thus remove it from the
> pathkeys list.
>
> We have the same issue when generating sort_pathkeys. As a result, we
> may have the final output in the wrong order. There were several
> reports about this issue before, such as [1][2].
>
> To fix this issue, I'm thinking that we mark the grouping expressions
> nullable by grouping sets with a dummy RTE for grouping sets, something
> like attached.
>

Hi Tom, I'm wondering if you've got a chance to look into this issue.
What do you think about the fix?

Thanks
Richard