Horton

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

Fujii Masao <masao.fujii@gmail.com>

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From: Fujii Masao <masao.fujii@gmail.com>
To: Atsushi Torikoshi <torikoshia.tech@gmail.com>
Cc: Jim Jones <jim.jones@uni-muenster.de>, torikoshia <torikoshia@oss.nttdata.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-09-01T09:09:38Z
Lists: pgsql-hackers

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

On Mon, Sep 1, 2025 at 7:58 AM Atsushi Torikoshi
<torikoshia.tech@gmail.com> wrote:
>
>
>
> 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

+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.

The patch looks good to me. Barring any objections, I'm thinking to
commit the patch.

Regards,

-- 
Fujii Masao