Re: [SQL] how to change the type

OK, I'm kind of interested now in how the variable length attributes are
actually stored on disk, that you are able to increase them, but not
decrease?

I would have thought the other way around?

Chris

> -----Original Message-----
> From: Stephan Szabo [mailto:sszabo(at)megazone23(dot)bigpanda(dot)com]
> Sent: Friday, 7 December 2001 10:05 AM
> To: Christopher Kings-Lynne
> Cc: tinar; pgsql-sql(at)postgresql(dot)org
> Subject: RE: [SQL] how to chane the type
>
>
>
> On Fri, 7 Dec 2001, Christopher Kings-Lynne wrote:
>
> > What's the essential problem with changing column types in
> postgres? Is it
> > similar to the DROP COLUMN problem?
> >
> > If the answer is that the table format only has allocated
> enough space per
> > row for the existing type, then how is it possible that
> Stephen's hack below
> > will not break things?
>
> The hack below only works to change the max length of variable length
> attributes and only upward. I'd be very wary of trying to change the real
> type of a value except between ones that are bitwise compatible (like I
> think varchar and text are technically, but I'm not sure).
>
> > > The best way is to recreate the table and rename
> > > them around. If you *REALLY* don't want to do
> > > that and have a recent backup (yes, I'm serious),
> > > you can muck with pg_attribute and change
> > > atttypmod for the attribute in question
> > > (from 14 to 34).
>