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The Semantics of NULL in SQL Server 2008


The Semantics of NULL in SQL Server 2008

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Adolfo J. Socorro, Ph.D.
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Comments posted to this topic are about the item The Semantics of NULL in SQL Server 2008
Koen Verbeeck
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Nice article. It summarizes a lot of pitfalls, but I would've liked a paragraph on the behaviour of NULL in COUNT(*) and COUNT(DISTINCT *).


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Nice article.



Jason AKA CirqueDeSQLeil
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One way to avoid worrying about NULLs is never to use them, always declaring columns as not allowing NULLs and designating default values for "empty" or "unknown". This will save you keystrokes, especially when you want to check whether a column does not have a certain value. However, you will anyway probably have to write logic for when columns have the designated default values.

TERRIBLE!
VERY TERRIBLE!
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ajs-1102829 (8/23/2010)
Comments posted to this topic are about the item <A HREF="/articles/T-SQL/70808/">The Semantics of NULL in SQL Server 2008</A>

SQL2008???
What's the difference from the other versions of sqlserver or ANSI SQL?
paul.knibbs
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Isn't ANSI_NULLS set to OFF by default? So the behaviour in this article will only apply if you've explicitly set it to ON. I'd have thought that deserved more than a single-line comment right at the end!
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I would be interested to know what the impact of using NULL is on the storage space required for a Column. i.e. does a nullable nvarchar column save space over a non-nullable nvarchar column with an empty string in it?
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paul.knibbs (8/24/2010)
Isn't ANSI_NULLS set to OFF by default? So the behaviour in this article will only apply if you've explicitly set it to ON. I'd have thought that deserved more than a single-line comment right at the end!


The article says this: "The handling of NULLs as we have summarized follows the ANSI standard. However, Transact-SQL offers an extension for null processing: If the option ANSI_NULLS is set to OFF, comparisons between nulls, such as NULL = NULL, evaluate to TRUE." Quite correctly, this implies that ANSI_NULLS is ON by default, and only turned off if that's what you specify.

John
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Carlo Romagnano (8/24/2010)
One way to avoid worrying about NULLs is never to use them, always declaring columns as not allowing NULLs and designating default values for "empty" or "unknown". This will save you keystrokes, especially when you want to check whether a column does not have a certain value. However, you will anyway probably have to write logic for when columns have the designated default values.

TERRIBLE!
VERY TERRIBLE!


Constructive feedback, lalalalala.
Please elaborate why this is so terrible, that way we can all learn something.


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Quite correctly, this implies that ANSI_NULLS is ON by default, and only turned off if that's what you specify.

John


I understood the situation to be the opposite--e.g. ANSI_NULLS is OFF by default. The description of the SET ANSI_NULLS command in Books Online appears to agree with that, too.
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