Re: Emitting JSON to file using COPY TO

On Fri, Jan 19, 2024 at 4:10 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> if (opts_out->json_mode && is_from)
> ereport(ERROR, ...);
>
> if (!opts_out->json_mode && opts_out->force_array)
> ereport(ERROR, ...);
>
> Also these checks can be moved close to other checks at the end of
> ProcessCopyOptions().
>
> ---
> @@ -3395,6 +3395,10 @@ copy_opt_item:
>                 {
>                     $$ = makeDefElem("format", (Node *) makeString("csv"), @1);
>                 }
> +           | JSON
> +               {
> +                   $$ = makeDefElem("format", (Node *) makeString("json"), @1);
> +               }
>             | HEADER_P
>                 {
>                     $$ = makeDefElem("header", (Node *) makeBoolean(true), @1);
> @@ -3427,6 +3431,10 @@ copy_opt_item:
>                 {
>                     $$ = makeDefElem("encoding", (Node *) makeString($2), @1);
>                 }
> +           | FORCE ARRAY
> +               {
> +                   $$ = makeDefElem("force_array", (Node *)
> makeBoolean(true), @1);
> +               }
>         ;
>
> I believe we don't need to support new options in old-style syntax.
>
you are right about the force_array case.
we don't need to add force_array related changes in gram.y.


On Wed, Jan 31, 2024 at 9:26 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2024-Jan-23, jian he wrote:
>
> > > +           | FORMAT_LA copy_generic_opt_arg
> > > +               {
> > > +                   $$ = makeDefElem("format", $2, @1);
> > > +               }
> > >         ;
> > >
> > > I think it's not necessary. "format" option is already handled in
> > > copy_generic_opt_elem.
> >
> > test it, I found out this part is necessary.
> > because a query with WITH like `copy (select 1)  to stdout with
> > (format json, force_array false); ` will fail.
>
> Right, because "FORMAT JSON" is turned into FORMAT_LA JSON by parser.c
> (see base_yylex there).  I'm not really sure but I think it might be
> better to make it "| FORMAT_LA JSON" instead of invoking the whole
> copy_generic_opt_arg syntax.  Not because of performance, but just
> because it's much clearer what's going on.
>
I am not sure what alternative you are referring to.
I've rebased the patch, made some cosmetic changes.
Now I think it's pretty neat.
you can, based on it, make your change, then I may understand the
alternative you are referring to.