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From: jian he <jian.universality@gmail.com>
Date: Sat, 29 Mar 2025 14:46:37 +0800
Message-ID: 
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Subject: Re: in BeginCopyTo make materialized view using COPY TO instead of
 COPY (query).
To: Kirill Reshke <reshkekirill@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>,
 Tom Lane <tgl@sss.pgh.pa.us>,
	Michael Paquier <michael@paquier.xyz>
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On Thu, Mar 27, 2025 at 3:04=E2=80=AFAM Kirill Reshke <reshkekirill@gmail.c=
om> wrote:
> >
> > hi.
> > patch attached.
> > also cc to Tom,
> > since at that time, you are against the idea of ``COPY matview TO``.
>
> Hi! With this patch it is possible to COPY matview TO, but not regular
> view, which is surprising. Let's fix that?

create view v1 as select 1;
copy v1 to stdout;

if you specifying table name, not query, then
{
        cstate =3D BeginCopyTo(pstate, rel, query, relid,
                             stmt->filename, stmt->is_program,
                             NULL, stmt->attlist, stmt->options);
        *processed =3D DoCopyTo(cstate);    /* copy from database to file *
}
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.