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From: Daniel Verite <[email protected]>
To: Andrew Dunstan <[email protected]>
Cc: Masahiko Sawada <[email protected]>
Cc: Jian He <[email protected]>
Cc: Joe Conway <[email protected]>
Cc: Junwang Zhao <[email protected]>
Cc: Florents Tselai <[email protected]>
Cc: Andrey M. Borodin <[email protected]>
Cc: Dean Rasheed <[email protected]>
Cc: Davin Shearer <[email protected]>
Cc: PostgreSQL development <[email protected]>
Subject: Re: Emitting JSON to file using COPY TO
Date: Wed, 18 Mar 2026 15:37:23 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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

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

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

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

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

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


Best regards,
-- 
Daniel Vérité 
https://postgresql.verite.pro/

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