From: Tom Lane <tgl@sss.pgh.pa.us>
To: "David G. Johnston" <david.g.johnston@gmail.com>
cc: exe-dealer <exe-dealer@yandex.ru>,
        "pgsql-bugs@lists.postgresql.org" <pgsql-bugs@lists.postgresql.org>
Subject: Re: jsonb subscript operator returns null when key is fetched from
 table
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Comments: In-reply-to "David G. Johnston" <david.g.johnston@gmail.com>
	message dated "Mon, 12 Dec 2022 11:51:19 -0700"
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Date: Mon, 12 Dec 2022 14:09:21 -0500
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"David G. Johnston" <david.g.johnston@gmail.com> writes:
> Someone more experienced than I will need to actually do the debugging work
> though; hoping this reply will be seen by one of them.

Meh.  Somebody was cavalier about detoasting the subscript:

            jbvp = getKeyJsonValueFromContainer(container,
                                                VARDATA(path[i]),
                                                VARSIZE(path[i]) - VARHDRSZ,
                                                NULL);

Neither VARDATA nor VARSIZE are valid to apply to an arbitrary datum.
Apparently, nobody has ever tested this with a subscript value fetched
straight from disk :-(.  The given example accidentally works with
a NOT MATERIALIZED CTE because the whole thing gets stepwise folded
to constants.  Likewise, the expression with || accidentally works
because concatenation always yields a non-toasted result.

			regards, tom lane