Re: Demo: Modelling Cost of Travel Paths Between Towns

>>>> Attempts to mask NULLs with unknowns or any other value,
>>>> don't work. (you must not have read my prior posts
>>>> expounding the above point).
>>>
>>> Let's say ... value 0 to indicate unknown age.
>>
>> If two things have age 0,
>> is it true or false that their ages are equal?
>
> In one sense, they are equal, and in another we don't know.

Please read, Missing Information in CJ Date's "Intro to Db Systems" (Chapter 20 in his 6th Ed). Maybe you'll see why "NULLs and 3VL undermine the entire foundation of the relational model" (pg 587). Received on Fri Nov 19 2004 - 06:41:07 CET