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

On 20 Nov 2005 13:58:43 -0800, michael@xxxxxxxxxx wrote:

>
>Hugo Kornelis wrote:
(snip)
>> According to the ANSI specification, null has one and only one meaning:
>> it's a marker to represent the absence of a value.
>>
>> So it's neither unknown, nor empty.
>>
>
>This just seems plain wrong to me.

Hi Mike,

So it seems. And hardly surprising. After all, you already opened this
discussion with the admission that you had trouble grasping the concept
of NULL within SQL databases.

> It surely is an empty set - or an
>empty thing.

No, NULL is not an empty set (though there is some relation here - the
result of most aggregate functions on an empty set is defined to be NULL
in the SQL standard).

The datatype of my dog's age (in whole years) has to be an integer, not
a set. You can't store a set (not even an empty one) in a column that is
designed to hold integer values.

The age of my dog is also not an empty thing. My glass of Scotch on the
other hand - now, THAT's an empty thing! :-)

> The thing surely exists.

How do you know? Suppose I don't have a dog, than how could my dog ever
have an age?

If *MIGHT* exist. But it might just as well not.


>http://www.dictionary.com has this to say (among others):
>
>Mathematics. Of or relating to a set having no members

That's the fourth definition in The American Heritage(R) Dictionary of
the English Language, 4th ed. The third one, directly above it, reads:

"Amounting to nothing; absent or nonexistent: a null result."

And further down the page, you'll find this definition, taken from The
Free On-line Dictionary of Computing:

"<programming> A special value used in several languages to
represent the thing referred to by an uninitialised pointer.

<database> A special value that may be stored in some database
columns to represent an unknown, missing, not applicable, or
undefined value. Nulls are treated completely differently
from ordinary values when evaluating SQL expressions and there
are several SQL constructs for dealing with nulls."


>This is entirely consistent with Pick's null.

I guess that consistency with Pick was not the top priority when the
ANSI committee wrote down their definition of NULL.

(snipped rest of Pick description - we were discussing NULL in SQL,
remember?)

Best, Hugo
--

(Remove _NO_ and _SPAM_ to get my e-mail address)
.

Relevant Pages

  • Re: is this as easy as i think? finite complement topology
    ... >WTS want to show R is compact (with this topology) ... I thought you wanted to show taht ANY subset of R is compact with this ... >look at any non empty subset U. Complement of U is finite. ... =>empty set element of U (as the empty set is subset of every ...
    (sci.math)
  • Re: 3vl 2vl and NULL
    ... >> properties that are represented by the values in my database. ... >>> If I look at my empty mug I can truthfully say ... >> that stores the amount of liquid in your mug. ... >thinking of the cell has holding an empty set would make sense, ...
    (comp.databases.theory)
  • Re: Top generic pascal tips required
    ... Having any TDataSet descendant or database connection with property Active ... T*Query with empty SQL property. ... TActionList with empty OnUpdate event hadler. ... TDBGrid or TDataSource with empty DataSource and DataSet properties. ...
    (borland.public.delphi.language.objectpascal)
  • Re: Access/SQLServer Requery Recordsource
    ... If the recordset is empty, the detail section of the form will not ... alter the recordsource SQL, you need to do it in the form Open ... event or before the form Open event. ... a saved querydef as the source for the form. ...
    (microsoft.public.access.formscoding)
  • Re: Definition of functions.
    ... So what we are getting here is that for every non empty set x ... that formula contradicts set theory. ... ,this definition will lead to any non empty set having injection from ...
    (sci.math)