Re: RFC: Restructuring pg_aggregate

> -----Original Message-----
> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> Sent: 12 April 2002 03:54
> To: Bruce Momjian
> Cc: Hiroshi Inoue; Christopher Kings-Lynne;
> pgsql-hackers(at)postgresql(dot)org
> Subject: Re: RFC: Restructuring pg_aggregate
>
>
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > I think that is why Tom was suggesting making all the column values
> > NULL and removing the pg_attribute row for the column.
>
> That was not my suggestion.
>
> > With a NULL value, it
> > doesn't take up any room in the tuple, and with the pg_attribute
> > column gone, no one will see that row. The only problem is
> the gap in
> > attno numbering. How big a problem is that?
>
> You can't do it that way unless you're intending to rewrite
> all rows of the relation before committing the ALTER; which
> would be the worst of both worlds. The pg_attribute row
> *must* be retained to show the datatype of the former column,
> so that we can correctly skip over it in tuples where the
> column isn't yet nulled out.
>
> Hiroshi did this by renumbering the attnum; I propose leaving
> attnum alone and instead adding an attisdropped flag. That
> would avoid creating a gap in the column numbers, but either
> way is likely to affect some applications that inspect pg_attribute.

Applications like pgAdmin that inspect pg_attribute are being seriously
hacked to incorporate schema support anyway for 7.3. Personnally I'd be glad
to spend some time re-coding to allow for this, just to not have to answer
the numerous 'how do I drop a column' emails I get reguarly.

Regards, Dave.