Re: [HACKERS] Solution for LIMIT cost estimation

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От Hannu Krosing
Тема Re: [HACKERS] Solution for LIMIT cost estimation
Дата
Msg-id 38A8A349.7E543AAD@tm.ee
обсуждение исходный текст
Ответ на Solution for LIMIT cost estimation  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: [HACKERS] Solution for LIMIT cost estimation  (Don Baccus <dhogaza@pacifier.com>)
Список pgsql-hackers
Don Baccus wrote:
> 
> This is a FUNDAMENTAL concept in SQL, one that is mentioned in every
> SQL book I've seen.
> 
> The same person probably expects NULL = NULL to return true, too.
> 

IIRC SQL3 defines different /classes/ of nulls where the above could be 
true if the NULLs belong to the same class. 

I.e. the absence of an orange is equal to the absence of the same orange,
but not equal to the absence of an apple (and possibly another orange) ;)

I may of course be completely wrong, as I did not read it too carefully 
being after completely other things at that time. 

I also could not figue out the use for such a feature.

----------------
Hannu


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