May 1, 2010 at 5:21 pm
Comments posted to this topic are about the item Play with NULLIF
-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
May 1, 2010 at 5:45 pm
Cool question! Thank you. I think that nullif is one of the useful functions which is somewhat overlooked by many.
Oleg
May 2, 2010 at 9:55 pm
Good question but just raises another for me - when would you use NULLIF? It may be useful, but I am struggling to see where you would use it. Why would you want something to return NULL if two values are equal? Is it just easier than using a CASE statement?
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TITUS. Why, I have not another tear to shed;
--Titus Andronicus, William Shakespeare
May 2, 2010 at 11:15 pm
Really challenging question Bhuvanesh.. 🙂 But still am not clear with the output.. u are comparing 2 expressions in ur query... one is int with value 0 and the other is null... both are of different value.. then how the output is null? null can be output only if the 2 values taken for comparison are equal rite??!!! can u plz explain this?
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~Niths~
Hard Work never Fails 🙂
May 3, 2010 at 12:20 am
Scott Duncan-251680 (5/2/2010)
Good question but just raises another for me - when would you use NULLIF? It may be useful, but I am struggling to see where you would use it.
The most common use case, in my experience, is avoiding division by 0 errors when calculating percentages, proportions, etc:
SELECT SomeAmount * 100.0 / NullIf(SomeTotalAmount, 0) AS SomePercentage
http://poorsql.com for T-SQL formatting: free as in speech, free as in beer, free to run in SSMS or on your version control server - free however you want it.
May 3, 2010 at 12:41 am
Niths (5/2/2010)
But still am not clear with the output.. u are comparing 2 expressions in ur query... one is int with value 0 and the other is null... both are of different value.. then how the output is null?
in this question ' ' (blank) will be treated as INT type means 0
.So 0 equal to 0 will give expected result
-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
May 3, 2010 at 12:55 am
i think mostly we will be using this to avoid divide by ZERO error
May 3, 2010 at 1:20 am
Didn't even know such a function existed.
You learn something new everyday. Now I can go home 😀
May 3, 2010 at 3:20 am
Scott Duncan-251680 (5/2/2010)
Good question but just raises another for me - when would you use NULLIF? It may be useful, but I am struggling to see where you would use it. Why would you want something to return NULL if two values are equal? Is it just easier than using a CASE statement?
Agreed - very good question. NULLIF is, in my opinion, one of the most under-apprecaited functions in SQL.
Others have already pointed out that you can use it to avoid divide by zero errors. Another use is when a character column that is nullable has erroneously been populated with a mixture of NULLL and blank strings (instead of NULL). Now, if a report should list 'n/a' to represent the missing strings, you can use
COALESCE(NULLIF(ColumnName, ''), 'n/a')
The NULLIF changes empty strings to NULL (and keeps existing NULLs as they are); the COALESCE then replaces them all with 'n/a'.
A third usse is for comparing string columns that are nullable with the requirement that two NULL values should be considered equal. WHERE Column1 = Column2 will miss the NULL pairs. The usual way to work around this is to use
WHERE Column1 = Column2 OR (Column1 IS NULL AND Column2 IS NULL)
This gets awkward if there are other requirements as well, because you need extra parentheses to seperate the OR from the AND, like this:
WHERE Column18 > 27
AND (Column1 = Column2 OR (Column1 IS NULL AND Column2 IS NULL))
Using ISNULL can work around this - although the result is admittedly not trivial to understand:
WHERE Column18 > 27
AND NULLIF(Column1, Column2) IS NULL
AND NULLIF(Column2, Column1) IS NULL
The first NULLIF will return NULL if both columns are equal or Column1 is NULL; the second is NULL if both are equal or Column2 IS NULL. So they are only both NULL if the columns are equal or both are NULL.
As to your last question - it's not just easier than a CASE expression (not statement!), it is in fact the same. NULLIF(expr1, expr2) is defined as shorthand for CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END.
May 3, 2010 at 5:17 am
Thanks a lot Bhuvnesh!! 🙂
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~Niths~
Hard Work never Fails 🙂
May 3, 2010 at 7:30 am
Great question, thanks.
Hugo, thanks for the additional information and insight.
May 3, 2010 at 7:31 am
Great question. Learned two new things today:
* nullif
* how SQL converts an empty string to a numeric datatype.
Nice one!
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May 3, 2010 at 8:42 am
Thanks Hugo for the information, very useful.
May 3, 2010 at 8:47 am
Good question, Thanks. I also learned a lot from the discussion, thanks Hugo for the explanation.
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May 3, 2010 at 9:28 am
Good question. Thanks Hugo for the detailed explanation.
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