Then, both, does not form a candidate key, since the attribute ID alone is a candidate key. Suppose that a combination of name and dept name is sufficient to distinguish among members of the instructor relation. It is possible that several distinct sets of attributes could serve as a candidate key. Experts describe a candidate key as having “no redundant attributes” and being a “minimal representation of a tuple” in a relational database table. Candidate keyĪ candidate key is a specific type of field in a relational database that can identify each unique record independently of any other data. That is, if t1 and t2 are in r and t1 = t2, then t1.K = t2.K. If we say that a subset K of R is a superkey for r, we are restricting consideration to instances of relations r in which no two distinct tuples have the same values on all attributes in K. Formally, let R denote the set of attributes in the schema of relation r. The name attribute of the instructor, on the other hand, is not a superkey, because several instructors might have the same name. For example, the ID attribute of the relation instructor is sufficient to distinguish one instructor tuple from 29 others. In a relation, the super key is the set of attributes that are used to uniquely identify tuples in the relation. In other words, if all the values are the same for two or more attributes, this may create a problem.
That is, the values of tuples should be such that they must satisfy the non-redundancy condition. In a Database, the tuples or attributes need to be uniquely identified.
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