Re: Nullable columns or Separate table ?

Hi,

>Can someone give me a pure theoretical viewpoint on following ?
>
>Sometime an attribute in an entity is not always meaningful, so we
>define it as Nullable and store NULL value when it is not applicable. An
>alternate way is to define another table with same primary key and
>optional attribute(s) and the table will contain rows only when
>applicable.

From a purely logical pospective, Chris Date absolutely hates null as it isn't a well formed value, and is used for different things in different places in SQL.

As such I would say (Date must be theoretically correct), the second approach must be nearer the relational theory.

In fact I might even go so far to say I believe that null must be a feature of the SQL language and not of relational theory.

Regards

Andrew Wilson
BlueOffice Solutions ApS
Denmark Received on Thu Apr 27 2000 - 00:00:00 CEST