Re: DROP COLUMN misbehaviour with multiple inheritance

On 29 Sep 2002, Hannu Krosing wrote:

> On Sun, 2002-09-29 at 19:57, Tom Lane wrote:
> > Hannu Krosing <hannu(at)tm(dot)ee> writes:
> > > I'd propose that ADD ONLY would pull topmost attislocal up (reset it
> > > from the (grand)child) whereas plain ADD would leave attislocal alone.
> >
> > ADD ONLY? There is no such animal as ADD ONLY, and cannot be because
> > it implies making a parent inconsistent with its children.
>
> I meant ADD ONLY to be the exact opposite of DROP ONLY - it adds parent
> column and removes attislocal from children. Simple ADD would _not_
> remove attislocal from children with matching column.

Consistency requires that it be exactly the opposite. When you ADD
ONLY, you want only in the "local" table, so children still have a local
definition; OTOH, when you ADD (recursively) you want all children to
get non-local status.

Suppose
CREATE TABLE p (f1 int);
CREATE TABLE c (f2 int) INHERITS (p);
c.f2.attislocal = true

Now,
ALTER TABLE ONLY p ADD COLUMN f2 int
should leavy c.f2.attislocal alone, while
ALTER TABLE p ADD COLUMN f2 int
should reset it.

This is the opposite of your proposal, and I don't think it exists in
Tom's proposal.

I think this is also consistent with the fact that ONLY requires the
column to exist in all children, while non-ONLY creates it where it
doesn't exist, and merges (resetting attislocal if set -- it could be
inherited from some other parent) where it exists.

--
Alvaro Herrera (<alvherre[(at)]dcc(dot)uchile(dot)cl>)
"Nunca se desea ardientemente lo que solo se desea por razon" (F. Alexandre)