On Sun, 2002-09-01 at 13:28, Neil Conway wrote:
> Rod Taylor <rbt@zort.ca> writes:
>
> > On Sun, 2002-09-01 at 04:00, Neil Conway wrote:
> > > This patch fixes a minor inaccuracy in the documentation: NOT NULL
> > > is not synonymous with CHECK (xxx IS NOT NULL) -- for example,
> > > consider ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL',
> > > not a check constraint.
> >
> > Yeah, but they're still synonymous.
>
> How so? Their behavior is clearly different (note the case above, as
> well as any other situation in which the system attempts to determine
> if a column allows a NULL value).
>
> Since they are not interchangeable, they can't be synonyms.
The case you brought up is more of a bug or mis-implementation of alter
table / add primary key. I guess you're right. They're not, but they
should be.