Re: Reduce "Var IS [NOT] NULL" quals during constant folding

On Wed, 26 Mar 2025 at 19:31, Richard Guo <guofenglinux@gmail.com> wrote:
>
> On Wed, Mar 26, 2025 at 3:06 PM Tender Wang <tndrwang@gmail.com> wrote:
> > The comment about  notnullattnums in struct RangeTblEntry says that:
> > * notnullattnums is zero-based set containing attnums of NOT NULL
> > * columns.
> >
> > But in get_relation_notnullatts():
> > rte->notnullattnums = bms_add_member(rte->notnullattnums,
> >                                                                     i + 1);
> >
> > The notnullattnums seem to be 1-based.
>
> This corresponds to the attribute numbers in Var nodes; you can
> consider zero as representing a whole-row Var.

Yeah, and a negative number is a system attribute, which the Bitmapset
can't represent... The zero-based comment is meant to inform the
reader that they don't need to offset by
FirstLowInvalidHeapAttributeNumber when indexing the Bitmapset. If
there's some confusion about that then maybe the wording could be
improved. I used "zero-based" because I wanted to state what it was
and that was the most brief terminology that I could think of to do
that. The only other way I thought about was to say that "it's not
offset by FirstLowInvalidHeapAttributeNumber", but I thought it was
better to say what it is rather than what it isn't.

I'm open to suggestions if people are confused about this.

David