What is Candidate Key in Database?

A candidate key of a table is a combination of attributes that can be uniquely used to identify a database record without any extraneous data. Each table may have one or more candidate keys. One of these candidate keys is selected as the table primary key.

Candidate key of a database table must fulfill two rules:

1. at all times it holds in the relation assigned to that variable that there are no two distinct tuples (rows) with the same values for these attributes and

2. there is not a proper subset of this set of attributes for which (1) holds.

very good , it helps me to understand about candidate key . i think it will be vry much helpful for every body...
A candidate key of a table is a combination of attributes that can be uniquely used to identify a database record without any extraneous data. Each table may have one or more candidate keys. One of these candidate keys is selected as the table primary key.

Candidate key of a database table must fulfill two rules:

1. at all times it holds in the relation assigned to that variable that there are no two distinct tuples (rows) with the same values for these attributes and

2. there is not a proper subset of this set of attributes for which (1) holds.

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very good , it helps me to understand about candidate key . i think it will be vry much helpful for every body...
A candidate key of a table is a combination of attributes that can be uniquely used to identify a database record without any extraneous data. Each table may have one or more candidate keys. One of these candidate keys is selected as the table primary key.

didn't understand a bit..............................................................................................................................................................................................................................................................................................................................................................................................................................................

A candidate key is a key that uniquely identifies rows in a table. Any of the identified candidate keys can be used as the table's primary key. Candidate keys that are not part of the primary key are called alternate keys.

One can describe a candidate key as a super key that contains only the minimum number of columns necessary to determine uniqueness.

A candidate key is a key that uniquely identifies rows in a table. Any of the identified candidate keys can be used as the table's primary key. Candidate keys that are not part of the primary key are called alternate keys.

One can describe a candidate key as a super key that contains only the minimum number of columns necessary to determine uniqueness.

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which uniquely identify a record a table may have more than one candidate key from where one of key is used as primary key..................................................................................................................................................................................................................................................

which uniquely identify a record a table may have more than one candidate key from where one of key is used as primary key............................................................................................................................................

lol... koi example to de k samjha do.. ye kya bakwasiyat laga rakhi h sabne,.??

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A candidate key is a key that uniquely identifies rows in a table. Any of the identified candidate keys can be used as the table's primary key. Candidate keys that are not part of the primary key are called alternate keys.

One can describe a candidate key as a super key that contains only the minimum number of columns necessary to determine uniqueness.

To view the defination of candidate key and some more sql server interview questions and code visitClick Here and also have some good questionsMore

Candidate Key is the collection of all the columns which are eligible for primary key.

example:
Consider a table 'Vehicle'
The columns are [ vehicleno, engineno, vechName,...]

We can use vechileno or engineno for identifying records uniquely.

hence candidate key = { vechileno, engineno }

there fore primaryKey will be either vechileno or engineno

If primaryKey = vechileno,
then alternateKey will be engineno

For more details..
http://eoracle11g.blogspot.com

i like this answer .it helps to understand diff b/w primary key and candidate key..........................................................................................................................................................................................................................................................................................................okkkk

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A candidate key of a table is a combination of attributes that can be uniquely used to identify a database record without any extraneous data. Each table may have one or more candidate keys. One of these candidate keys is selected as the table primary key.
Candidate key of a database table must fulfill two rules:

1. at all times it holds in the relation assigned to that variable that there are no two distinct tuples (rows) with the same values for these attributes and

2. there is not a proper subset of this set of attributes for which (1) holds.

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Thanks a lot , can you
explain a bit more without much of a complication.!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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