SQL Clone
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


Play with NULLIF


Play with NULLIF

Author
Message
mtillman-921105
mtillman-921105
SSCommitted
SSCommitted (1.6K reputation)SSCommitted (1.6K reputation)SSCommitted (1.6K reputation)SSCommitted (1.6K reputation)SSCommitted (1.6K reputation)SSCommitted (1.6K reputation)SSCommitted (1.6K reputation)SSCommitted (1.6K reputation)

Group: General Forum Members
Points: 1552 Visits: 3852
Interesting question - thanks.

The explanation led me to wonder what other character CAST() would return with 0. I've found two:

select cast('+' as smallint)
select cast('-' as smallint)

But why should a negative or positive sign return a zero?

______________________________________________________________________
The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge. - Stephen Hawking
Paul White
Paul White
SSC-Dedicated
SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)

Group: General Forum Members
Points: 36876 Visits: 11361
@sknox:

I'm pretty sure Hugo posted the NULLIF 'solution' as a bit of fun - though the idea behind it is very clever and worth posting just for that.
My comment was intended to be humourous as much as anything else - I laughed when I saw Hugo's Whistling reply.
(I don't disagree with anything you wrote by the way)

Paul



Paul White
SQLPerformance.com
SQLblog.com
@SQL_Kiwi
Bhuvnesh
Bhuvnesh
SSChampion
SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)

Group: General Forum Members
Points: 13868 Visits: 4077
Adam Haines (5/3/2010)
I think it is also important to understand what is going on underneath the hood, when NULLIF is used. Unbeknownst to some, NULLIF is actually a case expression under the hood, which means it is subject to data type precedence. The second value is not always implicitly converted to the data type of the first value. Whichever side has the less data type precedence will be converted to the other data type. This can cause implict conversion errors, if the columns cannot be converted to the higher data type.

e.g.


DECLARE @t TABLE(fl int);

INSERT INTO @t VALUES (0);

DECLARE @var CHAR(1),
@var2 DATETIME
SET @var = ''
SET @var2 = GETDATE()

select nullif(fl, @var)
FROM @t
--Compute Scalar(DEFINESad[Expr1004]=CASE WHEN [fl]=CONVERT_IMPLICIT(int,[@var],0) THEN NULL ELSE [fl] END))

select nullif(fl, @var2)
FROM @t
--Compute Scalar(DEFINESad[Expr1004]=CASE WHEN CONVERT_IMPLICIT(datetime,[fl],0)=[@var2] THEN NULL ELSE [fl] END))




thats called having red meat with cold beer on beach....PERFECT fruit for this thread.

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
sknox
sknox
SSCarpal Tunnel
SSCarpal Tunnel (4.1K reputation)SSCarpal Tunnel (4.1K reputation)SSCarpal Tunnel (4.1K reputation)SSCarpal Tunnel (4.1K reputation)SSCarpal Tunnel (4.1K reputation)SSCarpal Tunnel (4.1K reputation)SSCarpal Tunnel (4.1K reputation)SSCarpal Tunnel (4.1K reputation)

Group: General Forum Members
Points: 4125 Visits: 2935
Paul White NZ (5/3/2010)
@sknox:
I laughed when I saw Hugo's Whistling reply.
Paul


So did I ... AFTER I'd already posted my reply. Oh, the wonders of asynchronous operations!
webrunner
webrunner
SSCrazy Eights
SSCrazy Eights (8.2K reputation)SSCrazy Eights (8.2K reputation)SSCrazy Eights (8.2K reputation)SSCrazy Eights (8.2K reputation)SSCrazy Eights (8.2K reputation)SSCrazy Eights (8.2K reputation)SSCrazy Eights (8.2K reputation)SSCrazy Eights (8.2K reputation)

Group: General Forum Members
Points: 8179 Visits: 4003
Great question. I learned that I should read more carefully. This question was about NULLIF (which I had never learned), not ISNULL! Blush

Thanks,
webrunner

-------------------
"I love spending twice as long and working twice as hard to get half as much done!" – Nobody ever.
Ref.: http://www.adminarsenal.com/admin-arsenal-blog/powershell-how-to-write-your-first-powershell-script

"Operator! Give me the number for 911!" - Homer Simpson

"A SQL query walks into a bar and sees two tables. He walks up to them and says 'Can I join you?'"
Ref.: http://tkyte.blogspot.com/2009/02/sql-joke.html
thecosmictrickster@gmail.com
thecosmictrickster@gmail.com
SSCarpal Tunnel
SSCarpal Tunnel (4.8K reputation)SSCarpal Tunnel (4.8K reputation)SSCarpal Tunnel (4.8K reputation)SSCarpal Tunnel (4.8K reputation)SSCarpal Tunnel (4.8K reputation)SSCarpal Tunnel (4.8K reputation)SSCarpal Tunnel (4.8K reputation)SSCarpal Tunnel (4.8K reputation)

Group: General Forum Members
Points: 4830 Visits: 940
Thanks for the info Hugo. I can now see where it would be useful in a couple of queries I have for some reports - where I was getting a potential division by zero, depending on the input data. I seem to remember putting a rather inelegant solution (in comparison) to handle it. Will have to revisit.



Scott Duncan

MARCUS. Why dost thou laugh? It fits not with this hour.
TITUS. Why, I have not another tear to shed;
--Titus Andronicus, William Shakespeare

psharma-1140604
psharma-1140604
SSC Journeyman
SSC Journeyman (78 reputation)SSC Journeyman (78 reputation)SSC Journeyman (78 reputation)SSC Journeyman (78 reputation)SSC Journeyman (78 reputation)SSC Journeyman (78 reputation)SSC Journeyman (78 reputation)SSC Journeyman (78 reputation)

Group: General Forum Members
Points: 78 Visits: 9
When you cast(blank('') as int), it returns 0. so when you compare 0 with 0 nullif returns NULL.
declare @a smallint
set @a= 0
select nullif(@a,0)

Ans: NULL
Dhruvesh Shah
Dhruvesh Shah
SSC Eights!
SSC Eights! (819 reputation)SSC Eights! (819 reputation)SSC Eights! (819 reputation)SSC Eights! (819 reputation)SSC Eights! (819 reputation)SSC Eights! (819 reputation)SSC Eights! (819 reputation)SSC Eights! (819 reputation)

Group: General Forum Members
Points: 819 Visits: 237
Awesome question. didn't know nullIf can be these much tricky...
Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum

































































































































































SQLServerCentral


Search