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Subject: Re: Emitting JSON to file using COPY TO
From: "Daniel Verite" <daniel@manitou-mail.org>
To: "Andrew Dunstan" <andrew@dunslane.net>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>,
 Jian He
 <jian.universality@gmail.com>,
 Joe Conway <mail@joeconway.com>,
 Junwang Zhao
 <zhjwpku@gmail.com>,
 Florents Tselai
 <florents.tselai@gmail.com>,
 Andrey M. Borodin <x4mmm@yandex-team.ru>,
 Dean Rasheed
 <dean.a.rasheed@gmail.com>,
 Davin Shearer <davin@apache.org>,
 PostgreSQL development <pgsql-hackers@postgresql.org>
In-Reply-To: <964a3377-d957-4a06-ad02-8228aefa65fc@dunslane.net>
Date: Wed, 18 Mar 2026 15:37:23 +0100
Message-Id: <fc61429f-76a1-4385-a2bd-999967da306f@manitou-mail.org>
Archived-At: <https://www.postgresql.org/message-id/fc61429f-76a1-4385-a2bd-999967da306f%40manitou-mail.org>
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	Andrew Dunstan wrote:

> Here's a v30 set that I hope fixes these issues.

Currently there's no difference in output between the null
json value and the SQL null.

postgres=3D# create table tbl  (j jsonb);
CREATE TABLE

postgres=3D# insert into tbl values('null');
INSERT 0 1

postgres=3D# insert into tbl values(null);
INSERT 0 1

postgres=3D# table tbl;
  j=20=20=20
------
 null
=20
(2 rows)

postgres=3D# copy tbl to stdout with (format json);
{"j":null}
{"j":null}

If we had to reload this file, we could not determine which
kind of null we had even though they are different at the SQL
level:

postgres=3D# select null::jsonb is distinct from 'null'::jsonb;
 ?column?=20
----------
 t

Does it have to be that way or are there valid distinct outputs
that  we could use to avoid this ambiguity?


Best regards,
--=20
Daniel V=E9rit=E9=20
https://postgresql.verite.pro/