Candidate Keys - Primary keys in Oracle

Posted on 2013-12-10
Medium Priority
Last Modified: 2013-12-10
This was the interview question I had :

What are candidate keys? Suppose three candidate keys have been identified. Which one will become the primary key? Can all three candidate keys be made into composite primary key?
Question by:d27m11y
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Assisted Solution

David earned 1000 total points
ID: 39708999
Second question, yes, provided the concatenated string that results is unique.

You answered the first question:  candidates are potential primary key fields.  Between the business requirements, and the architect, a selection must be made on what's the best choice.

An Internet search will yield you examples and specifics.


Author Comment

ID: 39709090
Can I say that candidate key is the key column that uniquely identifies the data in a row and the candidate key could be composite primary key provided it is unique.

Please confirm if I understand right !
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Expert Comment

ID: 39709170
Correct.  Candidate key is the classroom term, I'm told.  Oracle does not use the term, but does use the concept.
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Accepted Solution

awking00 earned 1000 total points
ID: 39709412
>>Can I say that candidate key is the key column that uniquely identifies the data in a row<<
I would say it slightly differently -
A candidate key is a column or combination of columns that will always define a unique row.
Assume table x has cola, colb, and colc with the following values:
a1, b1, c1
a2, b2, c2
a3, b3, c3
In this case uniqueness can be defined by [cola], [colb], [colc], [cola,colb], [cola,colc], [colb,colc), or [cola,colb,colc]
However, if table x could have a row such as a1, b2, c3, the only candidate key would be [cola,colb,colc]

>>and the candidate key could be composite primary key provided it is unique.<<
Correct as demonstrated above

Author Closing Comment

ID: 39709430

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