A dynamic column cannot be NULL, so using a JSON null (a different kind of
null) to express "dynamic column exists but cannot be represented as
requested" should work. The ORM would then have the names and positions in
the structure of all the BINARY dynamic columns. With that it can send a
SELECT with one or more COLUMN_GET(dyncol_blob, "name" AS BINARY)
expressions. I could live with that.
Hmm. May be a dynamic column cannot be NULL now, but this is not a
conceptual limitation, there is no logical reason why it coldn't be.
So I'd rather keep JSON null for that. What I mean was that the whole
COLUMN_GET should fail and return NULL, just as any function does when
it gets invalid input:
MariaDB [test]> select uncompress("foobar"), 1/0, sqrt(-2);
+----------------------+------+----------+
| uncompress("foobar") | 1/0 | sqrt(-2) |
+----------------------+------+----------+
| NULL | NULL | NULL |
+----------------------+------+----------+
(it can also throw a warning, like uncompress does).
