Re: [HACKERS] Re: NULL & NOT NULL

"Thomas G. Lockhart" <lockhart@alumni.caltech.edu> writes:
>>>>>> create table authors (
>>>>>> zip             char(5)         null
>>>>>> );

> Sheesh. After that long song and dance about why we can't implement
> this, it turns out that it works fine. We had been trying to implement a
> slightly different syntax, "WITH NULL", which conflicted with the
> SQL92-defined data type declaration "TIMESTAMP WITH TIME ZONE".

> The "Practical SQL Handbook"-compatible form will be available in the
> next full release of Postgres. Thanks.

Now that we have the syntax problem straightened out: I'm still confused
about the semantics.  Does a "NULL" constraint say that the field
*must* be null, or only that it *can* be null (in which case NULL is
just a noise word, since that's the default condition)?  I had assumed
the former, but Bruce seemed to think the latter...
        regards, tom lane