Re: BUG #13442: ISBN doesn't always roundtrip with text

Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> writes:
>>> I have a table containing ISBNs stored as the isbn type provided by the isn
>>> extension. In certain cases an ISBN in ISBN10 form is considered unequal to
>>> the same ISBN in ISBN13 form.

> So I would say there is no bug as the number are indeed different, or that
> I missed something.

I think this definitely indicates a bug:

regression=# select '9791020902573'::isbn;
isbn
---------------
10-209-0257-4
(1 row)

regression=# select '10-209-0257-4'::isbn;
isbn
---------------
1-02-090257-4
(1 row)

I don't mind if '9791020902573' gets converted to something canonical,
but surely the canonical value ought to reproduce without further change.

Furthermore,

regression=# select '9791020902573'::isbn = '10-209-0257-4'::isbn;
?column?
----------
f
(1 row)

so apparently the canonicalization conversion wasn't right to begin with.

I have no idea which of these forms should be considered valid or
canonical, but surely the two behaviors exhibited above are wrong.

regards, tom lane