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

On Wed, Apr 2, 2025 at 11:20 PM Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
> >
> > if (!RelationIsPopulated(rel))
> > ereport(ERROR,
> > errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
> > errmsg("cannot copy from unpopulated
> > materialized view \"%s\"",
> > RelationGetRelationName(rel)),
> > errhint("Use the REFRESH MATERIALIZED VIEW
> > command to populate the materialized view first."));
>
> I think it's better to use the same hint message as the one output by
> "COPY (SELECT * FROM <unpopulated matview>) TO",
> specifically: "Use the REFRESH MATERIALIZED VIEW command," for consistency.
>
ok.

>
> >> The copy.sgml documentation should clarify that COPY TO can
> >> be used with a materialized view only if it is populated.
> >>
> > "COPY TO can be used only with plain tables, not views, and does not
> > copy rows from child tables or child partitions"
> > i changed it to
> > "COPY TO can be used with plain tables and materialized views, not
> > regular views, and does not copy rows from child tables or child
> > partitions"
>
> It would be clearer to specify that "COPY TO" applies to *populated*
> materialized views rather than just "materialized views"?
>
>
> > Another alternative wording I came up with:
> > "COPY TO can only be used with plain tables and materialized views,
> > not regular views. It also does not copy rows from child tables or
> > child partitions."
>
> If we split the first description into two as you suggested,
> I'm tempted to propose the following improvements to enhance
> the overall descriptions:
>
> -------------
> "COPY TO" can be used with plain tables and populated materialized views. For example, "COPY table TO" copies the same rows as "SELECT * FROM ONLY table." However, it doesn't directly support other relation types, such as partitioned tables, inheritance child tables, or views. To copy all rows from these relations, use "COPY (SELECT * FROM table) TO."
> -------------
>

your wording makes sense to me.
I try to ensure that the changing part in copy.sgml the line width
is less than 80 characters.
but I also want to make sure "<>" "</>" within the same line.
so after the change it becomes:

<para>
<command>COPY TO</command> can be used with plain
tables and populated materialized views.
For example,
<literal>COPY <replaceable class="parameter">table</replaceable>
TO</literal>
copies the same rows as
<literal>SELECT * FROM ONLY <replaceable
class="parameter">table</replaceable></literal>.
However it doesn't directly support other relation types,
such as partitioned tables, inheritance child tables, or views.

> The tests seem to have been placed under the category "COPY FROM ... DEFAULT",
> which feels a bit misaligned. How about adding them to the end of copy.sql instead?
>
ok.