A superkey is an attribute or combination of attributes in a relation that identifies a tuple uniquely within the relation. A superkey is the most general type of key. It is a set of one or more attributes (columns), which can uniquely identify a row in a table. For example, in a relation STUDENT consists of different attributes like Registration No, Name, Father Name, Class and Address. The only attribute that can uniquely identify a Tuple in a relation is Registration No. The Name attribute cannot identify a tuple because two or more students may have the same Name. Similarly, Father Name, Class and Address cannot be used to identify a tuple. It means that Registration No is the super key for the relation. Any combination of attributes with the super key is also a super key. It is an intimately related concept where the super key is reduced to the minimum number of columns required to uniquely identify each row.
It. means any attribute or set of attributes combined with the super key Registration No will also become a super key. A combination of two attributes (Registration No, Name} is also a super key. This combination can also be used to identify a tuple in a relation. Similarly (Registration No, Class} or {Registration No, Name, Class} are superkeys.
