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From: Richard Guo <guofenglinux@gmail.com>
Date: Fri, 8 May 2026 17:35:27 +0900
Message-ID: <CAMbWs4-yH6nsC4na99rWeXzA+sLXvJdtcevgkQDEU6RwJNbFKQ@mail.gmail.com>
Subject: Re: BUG #19418: SQL/JSON JSON_VALUE() does not conform to ISO/IEC
 9075-2:2023(E) 6.34 <JSON value constructor>
To: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Cc: Melanie Plageman <melanieplageman@gmail.com>, Nathan Bossart <nathandbossart@gmail.com>, 
	Tom Lane <tgl@sss.pgh.pa.us>, Amit Langote <amitlangote09@gmail.com>, 
	Vik Fearing <vik@postgresfriends.org>, lukas.eder@gmail.com, 
	pgsql-bugs@lists.postgresql.org, rmt@lists.postgresql.org, 
	=?UTF-8?Q?=C3=81lvaro_Herrera?= <alvherre@kurilemu.de>, 
	Heikki Linnakangas <hlinnaka@iki.fi>
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On Thu, May 7, 2026 at 11:45=E2=80=AFPM Ayush Tiwari
<ayushtiwari.slg01@gmail.com> wrote:
> The non-empty query form enforces the RETURNING typmod:
>
>   SELECT JSON_ARRAY(SELECT 1 RETURNING varchar(1));
>   ERROR:  value too long for type character varying(1)
>
> but the empty query form returns a value that does not fit the declared t=
ype:
>
>   SELECT JSON_ARRAY(SELECT 1 WHERE false RETURNING varchar(1));
>    json_array
>   ------------
>    []
>   (1 row)

Nice catch.  The empty-array Const was built with typmod -1, and the
type input function was invoked with typmod -1, so any RETURNING
length restriction was silently bypassed.

I've pushed a fix that builds Const and calls the input function with
the typmod of the non-empty COALESCE argument.

- Richard