Re: Weird Query

From: Maxim Demenko <mdemenko_at_gmail.com>
Date: Mon, 01 Aug 2005 21:47:11 +0200
Message-ID: <dclu7e$i7k$04$1@news.t-online.com>

AK schrieb:

>>>You know, the '' is equivalent to NULL.

>
> <<
>
> I have some reservations, such as:
>
> situation A:
> First Name: 'John'
> Middle Name: '' (unknown, not a required field)
> Last Name: 'Smith'
>
> situation B:
> First Name: 'Igor'
> Middle Name: '' (a known fact: no middle name at all. Russians do not
> have middle names. Patronymic names are not middle names)
> Last Name: 'Petrov'
>
> how would you distinguish between situations A and B?
>

 From the point of view entity "person" both cases are identical. For both rows attribute "Middle Name" has no value. That is NULL. If you will distinguish that rows, you should recognize, that a ability to posess a middle name is only due to affiliation of certain person to   certain category of people ( nation, whatever ). So ,to be able to distinguish these cases you need to introduce new entity , ( e.g. nation ), one of those attribute can be "middle name allowed" and create a relationship between that 2 entities.

Best regards

Maxim Received on Mon Aug 01 2005 - 14:47:11 CDT