From: Tom Lane <tgl@sss.pgh.pa.us>
To: bajinsheng@u.nus.edu
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18222: Unexpected Error--Cannot delete from scalar
In-reply-to: <18222-de86a89e6ed68f3d@postgresql.org>
References: <18222-de86a89e6ed68f3d@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Mon, 04 Dec 2023 05:56:09 +0000"
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Date: Mon, 04 Dec 2023 09:15:46 -0500
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PG Bug reporting form <noreply@postgresql.org> writes:
> SELECT ('1'-to_hex(2))::BOOLEAN; -- ERROR:  cannot delete from scalar

> This error looks strange to me as I do not understand what this error
> means.

Just out of curiosity, what did you expect that to do?

to_hex() produces type text, and there's no "text - text" operator.
What's evidently happening is that the parser finds "jsonb - text"
(i.e., jsonb_delete) as the only potentially applicable operator.
It successfully coerces '1' to a scalar jsonb value, but then
jsonb_delete() spits up because it's expecting an array.

I'm not sure that it was such a great idea to define '-' as having
this meaning for jsonb, but it's been there awhile now so probably
too late to change.

			regards, tom lane