T-SQL

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T-SQL

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Toreador SSChampion Points: 11365 More actions · Answer 1

mtassin (1/4/2013)
Since Uniqueness constraints basically enforce what they do with Unique Indexes, I was thinking that nobody uses Unique constraints anymore and just uses unique indexes since they can be filtered. 🙂

A unique index can also contain INCLUDEd columns, whereas the index generated by a unique coinstraint cannot.

mtassin SSC-Insane Points: 23099 More actions · Answer 2

Sean Lange (1/4/2013)
SQLRNNR (1/3/2013)
I have to disagree with the correct answer(s). The question asks for 4 correct answers yet 5 are presented. This causes a bit of a guessing game.
+1
I had to guess which 4 of the 5 correct answers were expected. I chose incorrectly.

Lol Join the club 🙂

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sburcombe SSCrazy Points: 2460 More actions · Answer 3

sburcombe

SSCrazy

Points: 2460

January 4, 2013 at 7:44 am

#1573756

Poorly worded question.

+1

Simone

Dana Medley SSCertifiable Points: 6764 More actions · Answer 4

Sean Lange (1/4/2013)
SQLRNNR (1/3/2013)
I have to disagree with the correct answer(s). The question asks for 4 correct answers yet 5 are presented. This causes a bit of a guessing game.
+1
I had to guess which 4 of the 5 correct answers were expected. I chose incorrectly.

+ 1

Everything is awesome!

kaspencer SSCarpal Tunnel Points: 4880 More actions · Answer 5

I feel sure that this was a misleading question, as five, not four, of the answers were valid.

The reputation of these questions is once again dragged through the gutter.

Kenneth Spencer

You never know: reading my book: "All about your computer" might just tell you something you never knew!
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(Bob Brown) SSCrazy Points: 2705 More actions · Answer 6

Lively debate today. It seems it is very hard to write a question of this sort without some confusion attached. Straight SQL questions with unequivocal results seem to be the best bet.

PChiragS SSCarpal Tunnel Points: 4965 More actions · Answer 7

Dineshbabu (1/3/2013)
Since last option said Unique key allows NULL values.. he didn't mention xactly one NULL value in the option . so I choosed other 4 and got it correct..
--
Dineshbabu

Dineshbabu is right..

the options says NULL Values, not exactly one NULL.

Thank You.

Lynn Pettis SSC Guru Points: 442467 More actions · Answer 8

SQLRNNR (1/3/2013)
dineshbabus (1/3/2013)
oh.. unique constraint can allow more than one null value.. I don't think so.. Please give me some xample...
Here is the example
http://www.sqlservercentral.com/Forums/FindPost1398825.aspx

Took this a bit further. You can only have one of each record:

CREATE TABLE sometest (testid INT, col1 INT, col2 INT);

ALTER TABLE sometest

ADD CONSTRAINT someconstraint UNIQUE (testid,col1,col2);

INSERT INTO sometest(testid,col1,col2)

VALUES (NULL,1,1),(1,NULL,1),(NULL,NULL,NULL),(1,1,NULL);

SELECT *

FROM sometest;

INSERT INTO sometest(testid,col1,col2)

values(null,null,NULL);

SELECT *

FROM sometest;

DROP TABLE sometest;

TomThomson SSC Guru Points: 104773 More actions · Answer 9

SQLRNNR (1/3/2013)
I have to disagree with the correct answer(s). The question asks for 4 correct answers yet 5 are presented. This causes a bit of a guessing game.

I too disagree with the correct answers.

But actually only 4 correct answers are presented - the first one., although claimed to be correct, says the are different but that doesn't identify any difference, so shouldn't be included when listing differences.

Anyway, it's certainly not a well designed question!

Tom

Toreador SSChampion Points: 11365 More actions · Answer 10

pchirags (1/4/2013)
the options says NULL Values, not exactly one NULL.

create table temp

(a int, b int, constraint ukTemp unique (a,b))

go

insert into temp values (null,null),(null,1),(1,null)

go

Three rows contain Null values. One of them contains two.

TomThomson SSC Guru Points: 104773 More actions · Answer 11

Dineshbabu (1/3/2013)
I think few days back same conversation happened... Unique constraint is different from unique index. While creating unique index we can create with filter and that will allow more than one NULL value but not with unique constraint.
--
Dineshbabu

create table #Test (P int identity primary key, A int, B int, unique(A,B))

insert #Test(A,B) values(1,NULL),(2,NULL),(3,NULL),(NULL,1),(NULL,2),(NULL,3)

insert #Test(A,B) values (NULL,NULL)

select * from #Test order by P

drop table #TestTry running that code and you'll see that despite teh unique constraing column A has 4 rows with NULL in it, and column B has 4 rows with null in it. In fact there are 7 rows and in every one of them either A or B or both are null.

Your statement about only one null being permitted is valid only when the unique constraint applies to a single column; it is not valid when it applies to multiple columns.

Tom

Victor Abkin SSC-Addicted Points: 426 More actions · Answer 12

I disagree with the list of correct answers: this list should contain 5 answers, not 4.

Asking to choose 4 answers makes it confusing

SQLDoubleG Hall of Fame Points: 3100 More actions · Answer 13

Bobby Russell (1/4/2013)
Poorly worded question. The 4 items I selected were the BEST possible of the 5 that ARE ACTUALLY CORRECT answers AS STATED and has been pointed out by everyone else here already. Sadly, his choice of what is CORRECT are not mine and thus I am WRONG. I'll miss my point. :Whistling:

Totally right, I want my point back 😀

Toreador SSChampion Points: 11365 More actions · Answer 14

Victor Abkin (1/4/2013)
I disagree with the list of correct answers: this list should contain 5 answers, not 4.
Asking to choose 4 answers makes it confusing

There are 4 correct ansers - 2,4,5 and 6 - just not the answers marked as being correct.

(Bob Brown) SSCrazy Points: 2705 More actions · Answer 15

Toreador (1/4/2013)
Victor Abkin (1/4/2013)
I disagree with the list of correct answers: this list should contain 5 answers, not 4.
Asking to choose 4 answers makes it confusing
There are 4 correct ansers - 2,4,5 and 6 - just not the answers marked as being correct.

Is number 3 an incorrect statement?