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From: jian he <jian.universality@gmail.com>
Date: Thu, 7 Mar 2024 12:08:21 +0800
Message-ID: <CACJufxGtetrn34Hwnb9D2if5D_HOPAh235MtEZ1meVYx-BiNtg@mail.gmail.com>
Subject: Re: remaining sql/json patches
To: Andy Fan <zhihuifan1213@163.com>
Cc: Amit Langote <amitlangote09@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, 
	Erik Rijkers <er@xs4all.nl>, Andres Freund <andres@anarazel.de>, Andrew Dunstan <andrew@dunslane.net>, 
	PostgreSQL-development <pgsql-hackers@postgresql.org>, pgsql-hackers@lists.postgresql.org, 
	Peter Eisentraut <peter@eisentraut.org>
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On Tue, Mar 5, 2024 at 12:38=E2=80=AFPM Andy Fan <zhihuifan1213@163.com> wr=
ote:
>
>
> In the commit message of 0001, we have:
>
> """
> Both JSON_VALUE() and JSON_QUERY() functions have options for
> handling EMPTY and ERROR conditions, which can be used to specify
> the behavior when no values are matched and when an error occurs
> during evaluation, respectively.
>
> All of these functions only operate on jsonb values. The workaround
> for now is to cast the argument to jsonb.
> """
>
> which is not clear for me why we introduce JSON_VALUE() function, is it
> for handling EMPTY or ERROR conditions? I think the existing cast
> workaround have a similar capacity?
>

I guess because it's in the standard.
but I don't see individual sql standard Identifier, JSON_VALUE in
sql_features.txt
I do see JSON_QUERY.
mysql also have JSON_VALUE, [1]

EMPTY, ERROR: there is a standard Identifier: T825: SQL/JSON: ON EMPTY
and ON ERROR clauses

[1] https://dev.mysql.com/doc/refman/8.0/en/json-search-functions.html#func=
tion_json-value