April 13, 2010 at 2:40 am
I opted for the NULL answer. My understanding was, and still is, that NULL doesn't mean unknown, but that any potential value is simply not there.
April 13, 2010 at 5:05 am
For me, NULL is definitely not «Unknown», since «Unknown» is a result of a logical operation.
Being in doubt i voted for NULL, but the question should have had more explanation.
April 13, 2010 at 6:31 am
NULL means the absense of a value....
NULL means NULL.
NULL does not equal NULL which is very different statement from means.
Kev -=Conan The Canadian=-
@ConanTheCdn
April 13, 2010 at 6:41 am
And what about not mentioned option "empty value". For numerics it is clear, but for strings, it's dangerous to mix with empty string.
NULL is unassigned value - no value at all, UKNOWN is special logical value, and zero/'' are normal values.
April 13, 2010 at 7:08 am
For a question about NULL to make any sense, the context and/or the operational definition must be set.
NULL has different results in the same operations based on other settings, therefore, NULL has different definitions based on those settings.
None of that is counting certain segments of actual practice, (not theory) in which the operational definition of NULL is actually 'Treat it as you treat empty string or 0 or some other known value, because those who came before failed to set the column to be NOT NULL for one or more reasons, and we aren't allowed to change the data or the setting now'.
April 13, 2010 at 7:13 am
Another trick question with poor wording.
April 13, 2010 at 7:17 am
I supplied the desired answer to this question, but only because I looked it up to get Microsoft's answer. While Microsoft clearly states "A value of NULL indicates that the value is unknown," (Books Online 2008) I absolutely do not agree with their definition since it is not based on any specified rationale. The correct answer is NULL.
I hold a doctorate in Computer Science and have well over 40 years in this business, so I predate Microsoft. You can believe me when I say that the concept of NULLs existed long before Microsoft and it has always meant the nonexistence of a value. According to Microsoft, there possibly is a value, but you just don't know what it is. I'm sorry, but that is not a proper definition of the concept. If a value does not exist, it is "known" to not exist, therefore it is by definition not "unknown". This is just as bad as people misusing the word "unique" by qualifying it with "more" or "most". Unique has no degrees. It is an absolute. By specifying a degree of uniqueness, one implies that the object is not unique. NULLness is an absolute lack of existence and may not be qualified by implying it is merely "unknown", because that implies the potential for non-NULLness.
April 13, 2010 at 7:25 am
Irish Flyer (4/13/2010)
... This is just as bad as people misusing the word "unique" by qualifying it with "more" or "most". Unique has no degrees. It is an absolute. By specifying a degree of uniqueness, one implies that the object is not unique. NULLness is an absolute lack of existence and may not be qualified by implying it is merely "unknown", because that implies the potential for non-NULLness.
Your comment is most optimal today 😀
Or optimalest is better (thanks to Alice)? :w00t:
April 13, 2010 at 7:26 am
Both question and answer are poorly worded. An unknown value implies the existence of a value. With NULL, there is no existence. NULL means NULL, regardless of what Microsoft says.
April 13, 2010 at 7:31 am
Like Irish, I to predate Microsoft, working in this field since early 70's. I am amazed at the responses, as I remember many years ago having it drilled into me the difference between NULL and "". The arguments then during many heated discussions are exactly the same as today. Many articles have been written explaining the differences and each author has their own take, not saying that each is wrong - just that this has always seemed to be a hot topic.
Steve Jimmo
Sr DBA
“If we ever forget that we are One Nation Under God, then we will be a Nation gone under." - Ronald Reagan
April 13, 2010 at 7:35 am
Null is not unknown. If I have a table of medical providers, the dob is null for a facility. That doesn't mean its unknown.
I chose null means null, because the other two were wrong and it said "null means null" not "null = null".
April 13, 2010 at 7:36 am
Unknown might be the BOL answer, but it doesn't help from either a practical sense or a conceptual sense. It is best to think of NULL as NULL.
A good example is a datetime field for an invoice delivery date. A value of NULL conveys that fact that the delivery has not been made. It doesn't convey that a delivery has been made, but is simply unknown. No value (NULL) has a known meaning.
April 13, 2010 at 7:54 am
The answer is simply answering a different question than the one given. The given question is "What does NULL mean?", not "What is result of a test with a NULL in it?" The only one of the answers given which even comes close to answering the given question is NULL.
NULL means NULL. What part of NULL don't you understand?
(I think it's the -ULL part -- most people get that wrong.)
April 13, 2010 at 8:03 am
As stated before - There are many articles written on this subject. Some that may help (these are not specific to SQL Server, thought the theory is the exact same):
http://www.databasedesign-resource.com/null-values-in-a-database.html
http://www.databasedev.co.uk/null_values_defined.html
These are just 2 of my favorites.
Steve Jimmo
Sr DBA
“If we ever forget that we are One Nation Under God, then we will be a Nation gone under." - Ronald Reagan
April 13, 2010 at 8:12 am
I think the answer might have been pulled from here:
http://databases.about.com/cs/sql/a/aa042803a.htm
I had to look this one up before answering because I had a feeling that I would get it wrong. My gut told me that NULL was NULL, not Unknown or zero but I had a feeling the author wouldn't have chosen that as the "correct" answer.
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