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

On Mon, Mar 31, 2025 at 11:27 PM Fujii Masao
<masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
>
> Regarding the patch, here are some review comments:
>
> + errmsg("cannot copy from materialized view when the materialized view is not populated"),
>
> How about including the object name for consistency with
> other error messages in BeginCopyTo(), like this?
>
> errmsg("cannot copy from unpopulated materialized view \"%s\"",
> RelationGetRelationName(rel)),
>
>
> + errhint("Use the REFRESH MATERIALIZED VIEW command populate the materialized view first."));
>
> There seems to be a missing "to" just after "command".
> Should it be "Use the REFRESH MATERIALIZED VIEW command to
> populate the materialized view first."? Or we could simplify
> the hint to match what SELECT on an unpopulated materialized
> view logs: "Use the REFRESH MATERIALIZED VIEW command.".
>
based on your suggestion, i changed it to:

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."));

>
> 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"

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."

>
> Wouldn't it be beneficial to add a regression test to check
> whether COPY matview TO works as expected?
sure.