Re: About #13489, array dimensions and CREATE TABLE ... LIKE

On Mon, 2023-11-20 at 21:13 -0500, Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > On Mon, Nov 20, 2023 at 09:04:21PM -0500, Tom Lane wrote:
> > > Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > > > An alternate approach would
> > > > be to remove pg_attribute.attndims so we don't even try to preserve
> > > > dimensionality.
>
> > > I could get behind that, perhaps. It looks like we're not using the
> > > field in any meaningful way, and we could simplify TupleDescInitEntry
> > > and perhaps some other APIs.
>
> > So should I work on that patch or do you want to try? I think we should
> > do something.
>
> Let's wait for some other opinions, first ...

Looking at the code, I get the impression that we wouldn't lose anything
without "pg_attribute.attndims", so +1 for removing it.

This would call for some documentation. We should remove most of the
documentation about the non-existing difference between declaring a column
"integer[]", "integer[][]" or "integer[3][3]" and just describe the first
variant in detail, perhaps mentioning that the other notations are
accepted for backward compatibility.

I also think that it would be helpful to emphasize that while dimensionality
does not matter to a column definition, it matters for individual array values.
Perhaps it would make sense to recommend a check constraint if one wants
to make sure that an array column should contain only a certain kind of array.

Yours,
Laurenz Albe