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How long is a NULL?


How long is a NULL?

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Arto Ahlstedt
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Comments posted to this topic are about the item How long is a NULL?
Bhavesh_Patel
Bhavesh_Patel
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I did not really knew that.



Bhavesh Patel

http://bhaveshgpatel.wordpress.com/
Steve Hall
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Does anyone know why it behaves like this? It appears to be at odds with any documentation I can find.

BrainDonor.

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Arto Ahlstedt
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The documentation is slightly different; 2005 BOL says that when "replacement_value" is returned, it will be implicitly converted to the type of "check_expression" while 2000 BOL just demands both expressions to be of same type.

This was the last straw for me, I haven't typed "ISNULL" into a code window since but switched to always using COALESCE.

Which I was expecting someone would mention. Perhaps there are circumstances where usage of ISNULL is warranted, but such use would require good commenting as most think of ISNULL and COALESCE as being equal.

COALESCE returns the full 10-character "replacement_value" in both versions.
ronmoses
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Wow, that is just bizarre. I wouldn't have called that in a million years, and I don't feel the least bit bad about getting it wrong. Great question!

-----
a haiku...

NULL is not zero
NULL is not an empty string
NULL is the unknown

paul.knibbs
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Yes, I found this bizarre behaviour the first time I encountered it. Just did a quick experiment on a SQL 2008 installation and I see it still does the same there, so guess we're probably stuck with this now. Pity, because it's utterly non-intuitive that NULL should have a size at all!
Carlo Romagnano
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Also a void string take 1 CHAR:

SET CONCAT_NULL_YIELDS_NULL ON
SELECT ISNULL('abcd'+''+null,'1234567890')

Result: 123456
sabyasm
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as well ..

SET CONCAT_NULL_YIELDS_NULL ON
SELECT ISNULL('abcd'+NULL+NULL,'1234567890')



Results : 123456


--
Sabya

Carlo Romagnano
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The question is:
it is a BUG?
... or it is by design?
... or both: it is a BUG by design!


Try this:

DECLARE @v char(10)
SET CONCAT_NULL_YIELDS_NULL ON
SELECT ISNULL('abcd'+@v,'1234567890')

RESULT: 1234567890

This behavior is all right!
Rudyx - the Doctor
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ahhh ... just another case of getting 'caught' by an 'implicit' converstion !

Regards
Rudy Komacsar
Senior Database Administrator

"Ave Caesar! - Morituri te salutamus."
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