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COALESCE Vs ISNULL


COALESCE Vs ISNULL

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Ujar
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Comments posted to this topic are about the item COALESCE Vs ISNULL
UMG Developer
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Nice question, thanks!
Hardy21
Hardy21
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Good one point question. Thanks

Thanks
Hardy21
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As per the BOL:
If all arguments are NULL, COALESCE returns NULL with Note: At least one of the null values must be a typed NULL.

Then why "SELECT COALESCE(NULL,NULL) AS [COALESCE]" is failed?

Thanks
Mike John
Mike John
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Because in this case ALL the arguments are "untyped" nulls.

so
declare @a int
select coalesce(@a,null)

will retunr NULL (and not an error).

Mike



sharath.chalamgari
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simple one today
philip.cullingworth
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An interesting question, but am I missing something here? When would you use coalesce entirely with untyped values?

If I were using coalesce it would be to test column values or variables/parameters and in both these cases typing is specified. Can anyone think of a situation where you would be sending only untyped values?
vk-kirov
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I found it interesting that the expression "ISNULL(NULL, NULL)" is of type INT.

SELECT ISNULL(NULL, NULL) AS A
INTO QOTD_TABLE;

EXEC sp_help 'QOTD_TABLE';

-- Column_name Type
-- ------------- ------
-- A int



Is there any reasonable explanation on this behavior?
paul.knibbs
paul.knibbs
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Interesting point there, vk-kirov. I guess that means that the default type for NULL is int--but in that case, there's not really any such thing as an "untyped NULL" and the COALESCE thing becomes a bit strange!
Koen Verbeeck
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Nice question.


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