Horton

Re: COPY TO: provide hint when WHERE clause is used

Atsushi Torikoshi <torikoshia.tech@gmail.com>

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From: Atsushi Torikoshi <torikoshia.tech@gmail.com>
To: Jim Jones <jim.jones@uni-muenster.de>
Cc: torikoshia <torikoshia@oss.nttdata.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-08-31T22:58:21Z
Lists: pgsql-hackers

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  1. Add HINT for COPY TO when WHERE clause is used.

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On Sun, Aug 31, 2025 at 3:14 AM Jim Jones <jim.jones@uni-muenster.de> wrote:
>
> Hi
>
> On 19.08.25 03:35, torikoshia wrote:
> > Considering what the user was trying to do, it might be helpful to
> > provide a similar hint in this case as well.
> > I’ve attached a patch that adds such a hint.
> >
> > What do you think?
> >
>
> +1
>
> I tested the patch and the error message now has the intended HINT ...
>
> postgres=# COPY t1 TO STDOUT WHERE i > 5;
> ERROR:  WHERE clause not allowed with COPY TO
> LINE 1: COPY t1 TO STDOUT WHERE i > 5;
>                           ^
> HINT:  Try the COPY (SELECT ... WHERE ...) TO variant.
>
> ... which aligns with the HINT from COPY TO from views
>
> postgres=# COPY v1 TO STDOUT;
> ERROR:  cannot copy from view "v1"
> HINT:  Try the COPY (SELECT ...) TO variant.

Thanks for your review!

Updated the patch to pass regression tests.