How do you count superkeys?
In general, if we have ‘N’ attributes with one candidate key then the number of possible superkeys is 2(N – 1). Example-2 : Let a Relation R have attributes {a1, a2, a3,…,an}. Find Super key of R. Maximum Super keys = 2n – 1.
What is the maximum no of superkeys for the relation?
The maximum number of super keys for the relation schema R ( E,F,G, H ) with E as the key is 23 = 8, because any subset of non key attributes along with key attribute will form the super key of R.
How many superkeys are there?
So the number of superkeys are 120.
How many candidate key is possible in given relation?
Total Number of Candidate Keys- Only one candidate key EFH is possible.
Which is a superkey of relation relation R?
The superkey is also known as superset key . If attribute set K is a superkey of relation R, then at all times it is the case that the projection of R over K has the same cardinality as R itself. A superkey is a set of attributes within a table whose values can be used to uniquely identify a tuple.
What is the number of possible super keys?
Thus we see that 4 Super keys are possible in this case. In general, if we have ‘N’ attributes with one candidate key then the number of possible superkeys is 2 (N – 1) . Example-2 : Let a Relation R have attributes {a1, a2, a3,…,an}.
Why is the set of all attributes a superkey?
It defines a functional dependency constraint from the superkey to all the attributes of the relation schema. The set of all attributes is a trivial superkey, because in relational algebra duplicate rows are not permitted: rows are a set (no duplicates), not a multiset (duplicates allowed). The superkey is also known as superset key .
How are super keys different from primary and candidate keys?
It’s different from the primary and candidate keys in the sense that only the minimal superkeys are the candidate/primary keys. This means that from a super key when we remove all the attributes that are unnecessary for its uniqueness, only then it becomes a primary/candidate key.