Re: BUG #19861: Self-join elimination drops a VOLATILE predicate and changes the query result

Tender Wang <tndrwang(at)gmail(dot)com> 于2026年11月11日周三 10:23写道：
>
> Hi,
>
> PG Bug reporting form <noreply(at)postgresql(dot)org> 于2026年11月11日周三 09:54写道：
> >
> > This occurs when self-join elimination is enabled for a primary-key
> > self-join with alias-specific calls to the same VOLATILE predicate.
> >
>
> After one relation is removed, SJE rewrites its Vars to reference the
> remaining relation.
> In this case, that turns
>
> is_odd_call(a.id)
> is_odd_call(b.id)
>
> into two structurally identical expressions referencing the same relation.
> fixup_selfjoin_quals() then treats the second expression as a
> duplicate and removes it.
> That is not valid for volatile expressions, since the two occurrences
> represent separately observable evaluations.
>
> The attached patch conservatively disables SJE when the query jointree
> contains volatile functions.
>

Checking in remove_useless_self_joins() seems too strict; it can skip
some self joins that have no volatile functions in quals.
I moved the check into remove_self_joins_one_group() as attached v2.

--
Thanks,
Tender Wang