Re: So what's null then if it's not nothing?

On 15 Dec 2005 14:33:16 -0800, vc wrote:

>
>Hugo Kornelis wrote:
>[...]
>> >>a couple of messages ago, that one of the
>> >> rules that form the foundation of SQL is this
>> >>
>> >> "1. NULLs propagate - any operation that has NULL as one of it's
>> >> operands results in NULL."
>> >
>> >Really ? What about 'FALSE AND NULL' evaluating to FALSE, or 'TRUE OR
>> >NULL' evaluating to TRUE ? See the original Codd's truth tables.
>>
>> AFAIK, there is no NULL in the original Codd's truth tables. Only True,
>> False and Unknown.
>
>Please reread the article in order to see that Codd uses letter 'w' to
>denote both NULL as a missing/unknown value and UNKNOWN as a truth
>value.

Hi vc,

Jon pointed me to that article in another message in this thread. I just replied to him. To avoid repeating myself, I'll just refer you to that message.

Best, Hugo

-- 

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