A superkey is a group of single or multiple keys which identifies rows in a table. A Super key may have additional attributes that are not needed for unique identification.
Super key is a set of columns on which all columns of the table are functionally dependent. It is a set of columns that uniquely identifies each row in a table.
Super key may hold some additional columns which are not strictly required to uniquely identify each row. Primary key and candidate keys are minimal super keys or you can say subset of super keys.
|STUDENT ID||STUDENT ROLLNO||STUDENT NAME||STUDENT MARKS|
Suppose we have a table that holds all the students in a college, and that table is called students information.
The table has columns called STUDENT ID, STUDENT ROLLNO, STUDENT NAME, and STUDENT MARKS. Every student has his/her own STUDENT ID, STUDENT ROLLNO, so that value is always unique in each and every row.