Unique constraint on a nullable column

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Home » Article Discussions » Article Discussions by Author » Discuss content posted by Marianna Petrovich » Unique constraint on a nullable column

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Unique constraint on a nullable column

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SanDroid

Posted Thursday, December 02, 2010 1:52 PM

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I am giong to get my point I lost back! Wink

Post #1029529

SanDroid

Posted Thursday, December 02, 2010 1:57 PM

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BowieRules! (12/2/2010)

I am sorry for confusing you with insert option, I only included it here because I found it on another blog as a solution to the problem, which I agree is not really a solution, but still a valid workaround, especially if it is put in a good InsertUpdate stored procedure.

This is not an administrative workaround and will not enforce the contraint from a DBA perspective.

It would not pass an Audit either. The other solutions listed would.

Cool

I am giong to get my point I lost back! Wink

Post #1029536

SanDroid

Posted Thursday, December 02, 2010 1:59 PM

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I am giong to get my point I lost back! Wink

Am I being greedy?

Post #1029539

sjimmo

Posted Thursday, December 02, 2010 2:27 PM

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SanDroid, I was wondering when you were going to show up Wink

(I need to get mine back as well Hehe

)

Steve Jimmo
Sr DBA
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Post #1029549

SanjayAttray

Posted Thursday, December 02, 2010 2:54 PM

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Got it right by fluke, but still trying to figure out how this one would resolve the issue:

Create a calculated column that is based on the column that allows nulls, and then define a UNIQUE constraint on the calculated column.

SQL DBA.

Post #1029560

SanDroid

Posted Thursday, December 02, 2010 3:00 PM

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SanjayAttray (12/2/2010)

Create a calculated column that is based on the column that allows nulls, and then define a UNIQUE constraint on the calculated column.

Sanjay, Some of the more creative minds at M$ actualy list this and how to do it as a solution to this "documented limitation" of TSQL RDBMS servers in a Q article.
http://support.microsoft.com/kb/322002

The solutions provided in this article are the only ones supported by M$.
ummm... Or at least that is the word on the street.... Cool

Still getting my POINT back w00t

Post #1029563

Glenn Dorling

Posted Thursday, December 02, 2010 4:31 PM

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The statement "I found it on another blog as a solution to the problem" worries we. Just because someone says something, especially on the internet, doesn't mean it's correct. As many have pointed out previously, enforcing something in the app isn't really enforcing anything at all, because as soon as someone uses a different app there's no enforcement at all.

(I'd also be very amused to watch how that "solution" scaled as the number of rows increased, unless I had to support it that is).

Post #1029587

L' Eomot Inversé

Posted Thursday, December 02, 2010 5:34 PM

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Well, as has been pointed out already the 5th "correct" option doesn't handle update statements at all and even for inserts it handles only single row inserts.

Nevertheless, it's a good question (despite that flaw in the answer) because it's thought-provoking. And I don't imagine I'm the only one who wasn't previously aware of Hugo's connect item and added a vote as a result of this, so with some luck the question has added a few votes that may help MS realise that this is a serious issue.

It raises an interesting side-issue: how bizarre does a "work-around" have to be before it ceases to count as a real work-around. I guess any answer to that is going to be subjective. For myself, I reckon a filtered index is a good work-around, and a trigger is a passable work-around. But I'll go along with an earlier comment about the computed column solution - why do I want to invent some weird imaginary column to do something that the SQL standard says I can do without it? It works, of course, but I don't like it one bit. Neither do I like the indexed view work-around, although of course that too works; but confusing an index (an access mechanism) with a view (a derived relation) seems to me to be a step too far from the relational model.

Tom
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Is minig a cheapas beul fosgailte dòrn dùinte.

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Post #1029601

SQLRNNR

Posted Thursday, December 02, 2010 10:51 PM

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This question seems dubious. 5 required correct answers and only worth 1 point?

Jason AKA CirqueDeSQLeil
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MCM SQL Server 2008

SQL RNNR

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Post #1029653

Mayank Parmar

Posted Friday, December 03, 2010 1:40 AM

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Hi,

It is always hard to get the right answer for this kind of question. There is more probability that you will miss at least one point.

So I think rather then giving 8 options together in 1 question, it should be distributed to 2 to 3 questions and then it would be better justice.

Regards,

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