On Mon, May 11, 2020 at 4:22 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > If the parent is RTI 1, and the children are RTIs 2..6, what
> > varno/varattno will we use in RTI 1's tlist to represent a column that
> > exists in both RTI 2 and RTI 3 but not in RTI 1, 4, 5, or 6?
>
> Fair question. We don't have any problem representing the column
> as it exists in any one of those children, but we lack a notation
> for the "union" or whatever you want to call it, except in the case
> where the parent relation has a corresponding column. Still, this
> doesn't seem that hard to fix. My inclination would be to invent
> dummy parent-rel columns (possibly with negative attnums? not sure if
> that'd be easier or harder than adding them in the positive direction)
> to represent such "union" columns.
Ah, that makes sense. If we can invent dummy columns on the parent
rel, then most of what I was worrying about no longer seems very
worrying.
I'm not sure what's involved in inventing such dummy columns, though.
--
Robert Haas
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