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# Difference between Unique Key and candidate key

Posted by Muhsinathk under Sql Server on 6/11/2012 8:19:36 AM | Points: 10 | Views : 7289 | Status : [Member] | Replies : 9

What is the difference between Unique Key and candidate key?

Posted by: Naraayanan on: 6/11/2012 [Member] Starter | Points: 25

Hi,
Check this link..
http://blog.sqlauthority.com/2009/10/22/sql-server-difference-between-candidate-keys-and-primary-key-2/

Regards,
Lakshmi Naraayanan.S
http://dotnettechrocks.blogspot.in/
http://abaprocker.blogspot.com/

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Posted by: Muhsinathk on: 6/11/2012 [Member] Bronze | Points: 25

http://www.coolinterview.com/interview/24530/

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Posted by: Muhsinathk on: 6/11/2012 [Member] Bronze | Points: 25

Thank you Naraayanan

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Posted by: Muhsinathk on: 6/11/2012 [Member] Bronze | Points: 25

Posted by: .Netlearner on: 6/11/2012 [Member] Starter | Points: 25

A candidate key is one that can identify each row of a
table uniquely. Generally a candidate key becomes the
primary key of the table. If the table has more than one
candidate key, one of them will become the primary key, and
the rest are called alternate keys.

A key formed by combining at least two or more columns is
called composite key.

Refer this link for further details :http://blog.sqlauthority.com/2009/10/22/sql-server-difference-between-candidate-keys-and-primary-key-2/

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Posted by: Akiii on: 6/11/2012 [Member] Bronze | Points: 25

An unique key and a primary key is a type of candidate key.

Thanks and Regards
Akiii

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Posted by: Muhsinathk on: 6/12/2012 [Member] Bronze | Points: 25

Thank youu

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Posted by: Sriramnandha on: 6/21/2012 [Member] Starter | Points: 25

Unique Key:

Unique key Restrict Duplicate Values and Null Values.Default Non Clustered index is an Unique Key

Example:

Create table Test(Testid int constraint pk_Test unique(Testid), TestName varchar(90))

Candidate Key:

Primary Key Alternative is an Candidate Key

Regards
Srriam.R

sriram

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Posted by: Gemamgall on: 6/27/2012 [Member] Starter | Points: 25

Candidate Key is a column in a table which has the ability to become a primary key.

Unique key is same as primary key but only difference is that unique key allows only one null value but primary does not allow even a single null value

Thanks and Regards,

Vinay Gandhi
www.quadtechindia.com

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