Re: [HACKERS] Solution for LIMIT cost estimation

At 02:52 AM 2/15/00 +0200, Hannu Krosing wrote:
>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. 

My recent foray into the SQL3 draft with Jan in order to figure out
MATCH <unspecified> semantics makes me suspicious of anyone's claim to
understand what the standard says :)

Particularly the authors!

I'm carrying a length of rope and am keeping mindful of the nearest
lamp post just in case I run across one in the street by accident.

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

Well, I just looked at Date's summary of SQL3 and while he talks 
about the new user datatype and mild object-oriented innovations,
he doesn't talk about any change in the meaning of NULL.  Since
he makes no effort to hide his loathing for NULL or three-valued
logic as implemented in SQL, if it had changed I'm certain he
would've mentioned it.



- Don Baccus, Portland OR <dhogaza@pacifier.com>
  Nature photos, on-line guides, Pacific Northwest
  Rare Bird Alert Service and other goodies at
  http://donb.photo.net.