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If there is more than one key for relation schema in DBMS then each key in relation schema is classified as

  1. prime key
  2. super key
  3. candidate key
  4. primary key
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CANDIDATE KEY is a set of attributes that uniquely identify tuples in a table. Candidate Key is a super key with no repeated attributes. The Primary key should be selected from the candidate keys. Every table must have at least a single candidate key. A table can have multiple candidate keys but only a single primary key

Both candidate key and super key can be more than one in a table

super-key-and-candidate-key

A super key with no redundant attribute is known as candidate key. Candidate keys are selected from the set of super keys, the only thing we take care while selecting candidate key is that the candidate key should not have any redundant attributes.Every candidate key is a super key but, every super key may or may not be a candidate key.All candidate keys are super keys.  so option C is more correct than Option B

A primary key is selected from the set of candidate keys.only one key possible per table or we can say it can not be possible more than one for one table so option A,D are wrong.

Option C

 

Answer:

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