Re: why generated columsn cannot be used in COPY TO?

On Friday, October 6, 2023, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> "David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> >> On 10/6/23 08:45, Ron wrote:
> >>> Nah. "The programmer -- and DBA -- on the Clapham omnibus" quite
> >>> reasonably expects that COPY table_name TO (output)" copies all the
> >>> columns listed in "\d table_name".
>
> > Sure, but it doesn't. Mainly since copy's original design was intended
> to
> > solve the dump/restore problem and it doesn't make sense to specify data
> > for inbound generated data. So while we do have a POLA violation here
> the
> > desirability to now fix it years later is basically zero. And the
> current
> > behavior is at least defensible and consistent. And there is a very easy
> > way to get the desired output making any change that much harder a sell.
>
> Changing the default behavior now is certainly a non-starter.
> I don't really see any backwards-compatibility problem with
> allowing cases that had been errors, though.
>

I wouldn’t vote against it but the current simplicity seems sufficient.
“Copy table doesn’t recognize generated columns, use copy (select) if you
want to include them in the output.”

David J.