Difference between Unique Key and candidate key

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

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Thank you Naraayanan

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http://dev.fyicenter.com/Interview-Questions/ORACLE-4/What_is_the_difference_between_candidate_key_un.html

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


Thanks and Regards
Akiii

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Thank youu

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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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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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