Re: how could a foreign key ever be NULL?

On Mon, 2001-12-17 at 11:38, Terrence Brannon wrote:
> The Momjian book states:
>
> A single-column foreign key is either NULL or matches a primary key
>
> But the problem I have with this statement is that a primary key
> cannot be null or duplicate. And since the foreign key references
> a value that is neither null or duplicate, how could it ever be
> NULL?

If the foreign key is NULL, it doesn't reference anything.  If this is
not a valid condition, the column should be declared as NOT NULL.

--
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
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