Re: Date, Darwen, Pascal and the alternative to Nulls in the RM
Date: Wed, 22 Mar 2006 13:53:45 GMT
Message-ID: <JFcUf.1551$kB1.1157_at_trndny07>
"Christopher Browne" <cbbrowne_at_acm.org> wrote in message news:87hd5rmbii.fsf_at_wolfe.cbbrowne.com...
> Now, I'm not arguing that NULLs are a wonderful thing, and we should
> be using them more. They *are* trouble. I had trouble with some
> NULLs today; a table that, at this point, is quite misdesigned. The
> NULLs in this pricing table were driving one of our QA guys batty; he
> was having great trouble trying to delete some rows. The absence of a
> primary key on the table was entirely troublesome; that will *HAVE* to
> change before the system gets into production...
If the absence of a primary key reveals the absence of any candidate keys, then the trouble is even worse.
>
> The only systematic "NULL evasion" seems to be to, in effect, "fork
> off" extra tables so that, where a value is omitted, you merely don't
> link it in. Unfortunately, that complicates the data model...
> --
A fully normalized model would have no nullable cells. One can construe nullable columns as the result of materializing outer joins on the normalized model. In practice, it's usually unnecessary to go through this exercise. Received on Wed Mar 22 2006 - 14:53:45 CET