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

Jim Jones <jim.jones@uni-muenster.de>

From: Jim Jones <jim.jones@uni-muenster.de>

To: torikoshia <torikoshia@oss.nttdata.com>, pgsql-hackers@lists.postgresql.org

Date: 2025-08-30T18:14:29Z

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Add HINT for COPY TO when WHERE clause is used.
- 229911c4bf9a 19 (unreleased) landed

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.

Best, Jim