Re: Database design question
Date: Mon, 26 Jun 2006 19:36:58 GMT
Message-ID: <uHWng.2597$pu3.62899_at_ursa-nb00s0.nbnet.nb.ca>
sreedhardasi_at_gmail.com wrote:
>>sreedhardasi_at_gmail.com wrote:
>>
>>
>>>I have a database design questions. How can we specify one of two
>>>columns in a table should be not null? In other words, if one column is
>>>
>>>null then another column should not be null.
>>
>>The simple answer is to avoid null in the first place. Null will affect
>>the validity of everything it touches.
>
> Thanks for your reply. How can we avoid nulls? If document has group
> level permissions, then what will be the value for the user id (Just
> blank)?
I might suggest the Principle of Orthogonal Design (POOD) would give some clues. I think you might get a few more from Fabian Pascal's _Practical Issues in Database Management_ -- especially the sections on sub-types. Received on Mon Jun 26 2006 - 21:36:58 CEST