Which one is correct w.r.t. RDBMS?
2017
Which one is correct w.r.t. RDBMS?
- A.
primary key ⊆ super key ⊆ candidate key
- B.
primary key ⊆ candidate key ⊆ super key
- C.
super key ⊆ candidate key ⊆ primary key
- D.
super key ⊆ primary key ⊆ candidate key
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Correct answer: B
In RDBMS, a super key is any set of attributes that uniquely identifies a tuple. A candidate key is a minimal super key, meaning no proper subset of it is also a super key. A primary key is selected from the candidate keys to uniquely identify records in a table. Therefore, every primary key is a candidate key, and every candidate key is a super key. This establishes the hierarchy: Primary Key ⊆ Candidate Key ⊆ Super Key.
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