Clarification of certain SQLSTATE class

I'm working with some DB2 users, converting them to Pg, and I'm a bit
confused about a certain class of SQLSTATE codes, specifically 02xxx "No
data" (http://www.postgresql.org/docs/9.2/static/errcodes-appendix.html)

As an example: I enable %e in log_line_prefix so I can see the SQLSTATE
values. I run an UPDATE against a non-existent row, and find that my
SQLSTATE value is 00000, indicating success. I understand that this could
be considered a 'success' because the query didn't actually throw an error;
but, based on the spec, I expected to see a SQLSTATE of 02000.

I thought that Pg always generated an appropriate SQLSTATE code, and that
it was just up to $client code to pick up that value, but that doesn't seem
to be the case. Is this part of the SQL standard we don't implement?

Thanks!

gabrielle