Re: in BeginCopyTo make materialized view using COPY TO instead of COPY (query).

On Sat, Mar 29, 2025 at 9:06 AM Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:

>
> On 2025-03-29 Sa 10:40 AM, David G. Johnston wrote:
>
> On Saturday, March 29, 2025, Kirill Reshke <reshkekirill(at)gmail(dot)com> wrote:
>
>> On Sat, 29 Mar 2025 at 09:47, jian he <jian(dot)universality(at)gmail(dot)com>
>> wrote:
>> >
>> > will use {table_beginscan, table_scan_getnextslot, table_endscan}
>> > to output the data.
>> > but views don't have storage, table_beginscan mechanism won't work.
>> >
>> > so i don't think this is possible for view.
>>
>> Well... So you are saying that let us have inconsistent features
>> because of how things are implemented in core... I don't sure I'm
>> buying that, but whatever, let's hear some other voices from the
>> community. My argument is that while we are working on it, perhaps we
>> should revise certain implementation specifics along the way. However,
>> this is merely my opinion on the matter.
>>
>
> At present copy {table} to only exists to support pg_dump. It is not
> marketed as a general purpose export facility.
>
>
> *ahem*
>
>
> What is your evidence for that proposition? If this were true we would not
> support CSV mode, which pg_dump does not use. It might have limitations,
> but its use goes far beyond just pg_dump, both in theory and practice.
>
>
>
>
"copy {subquery} to" is a general-purpose exporter that makes use of those
additional features. Sure, they also work for the narrowed case of "copy
{relation/table} to" but I make my claim on the very fact that {relation}
cannot be stuff like foreign tables or partitioned tables, which pg_dump
has no need to target.

David J.