RE: quick FK question

From: Sweetser, Joe <>
Date: Tue, 15 Dec 2009 14:31:59 -0700
Message-ID: <89FD2C8D7D551D4598EF20C7E42FEB450521D2E9_at_earthquake.ICAT.COM>

Perfect. Such an easy explanation once it is presented clearly.

Much appreciated,

-----Original Message-----
From: Stephane Faroult [] Sent: Tuesday, December 15, 2009 2:30 PM To: Sweetser, Joe
Subject: Re: quick FK question


   You have answered your own question. The FK says 'any value here must be found in the referenced table'. But as Chris Date would tell you, even if many people speak (wrongly) of "null values", NULL is not a value - it's the absence of a value. Nothing violates no constraints.


Sweetser, Joe wrote:
> I'm having trouble understanding FK's and NULL's. It appears I can
> insert a null value to a foreign key which is not what I would expect.
> Is the "solution" to put NOT NULL on the column definition?
> Thanks,
> -joe

Received on Tue Dec 15 2009 - 15:31:59 CST

Original text of this message