Re: PRIMARY KEY on a *group* of columns imply that each column is NOT

On Tue, Apr 26, 2005 at 03:48:44PM -0500,
 Scott Marlowe <smarlowe@g2switchworks.com> wrote
 a message of 26 lines which said:

> Here's a quote from the SQL1992 spec that's VERY clear:

Yes, PostgreSQL is right and implement the standard. Now, what's the
rationale for the standard? I understand it for a single column but,
for several columns, it should be still possible to have different
tuples, such as (3, NULL) and (5, NULL) for instance.