> 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?
Uh, you could have a foreign key row that doesn't match a primary key
row, and is hence NULL, can't you?
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
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