Re: BUG #19418: SQL/JSON JSON_VALUE() does not conform to ISO/IEC 9075-2:2023(E) 6.34 <JSON value constructor>

On Tue, Mar 3, 2026 at 11:42 AM jian he <jian.universality@gmail.com> wrote:
> On Thu, Feb 26, 2026 at 10:20 PM Vik Fearing <vik@postgresfriends.org> wrote:
> > > Try this:
> > >
> > >    select json_array(select 1 where false);
> > >
> > > It produces NULL, not []
> >
> >
> > I can confirm that postgres violates the standard here.
> >
> > --
>
> Since the subject title mentioned JSON_VALUE.
>
> SELECT JSON_VALUE(((select NULL where false)), '$');
> SELECT JSON_QUERY(((select NULL where false)), '$');
> SELECT JSON_EXISTS(((select NULL where false)), '$');
>
> Should the above produce []?

AFAIK about the standard, no. The empty-set -> '[]' rule is specific
to JSON_ARRAY(<query>), whose job is to collect rows into an array.
JSON_VALUE, JSON_QUERY, and JSON_EXISTS return a scalar, a JSON value,
and a boolean, respectively, not array-shaped values, so there's no
empty-array concept to invoke; empty-input behavior is governed by ON
EMPTY / ON ERROR.

-- 
Thanks, Amit Langote