Re: BUG #18222: Unexpected Error--Cannot delete from scalar

PG Bug reporting form <noreply(at)postgresql(dot)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