Super key is the combination one and more attribute to uniquely identify a tuple. For example, we have a student table with attribute (stu_rollno., stu_name, stu_add, stu_branch, stu_Aadharno.)
Here we can have several sets of a superkey as given below.
stu_rollno. + stu_name
stu_rollno. + stu_name + stu_branch
stu_Aadharno. + stu_name
stu_rollno. + Stu_Aadhar
stu_Aadharno. + stu_name + stu_branch
stu_rollno. + stu_name + stu_add
These were a few combinations of superkey that can identify the tuple value obsoletely.
However, stu_rollno. and stu_Aadharno is also a candidate key which is also capable to fetch the tuple value uniquely. So stu_rollno. and stu_Aadhar will be a minimal superkey which can easily identify the whole tuple value.
See, below another example for the same.
So, here we can say that super is key is the strong combination of attributes that which provide a guarantee to provide the unique tuple value.
Super key is different from the composite key. If in a case we don’t have any candidate key in our relationship then the combination of a possible attribute which can uniquely identify a tuple value is known as a comosite key.
Super key is the strong key which assures a guarantee to identify the tuple uniquely. Let’s have a relation with one candidate key with some other attributes which are not a key. Then a super key can be all possible combination of candidate key with the other attributes of the relation.
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