Difference between Super Key and Candidate Key

Tables in databases need ways to identify each record uniquely. Super keys and candidate keys help with this. They're special columns or groups of columns that can tell records apart. Both super keys and candidate keys can have empty spaces (null values). These keys also help connect different tables. While they sound similar, there are some differences between them. Super keys can have extra information that's not needed to identify records, but candidate keys only have the bare minimum needed. Understanding these keys is important when setting up and working with databases. Let's look at how they're different and why they matter.

What is Super Key?

Super Key is an attribute (or set of attributes) that is used to uniquely identify all attributes in a relation. All super keys can’t be candidate keys but the reverse is true. In relation, a number of super keys is more than a number of candidate keys. 

Example: We have a given relation R(A, B, C, D, E, F) and we shall check for super keys by following given dependencies : 

Functional dependenciesSuper key
AB->CDEF                                       YES
CD->ABEF                                       YES
CB->DF                                            NO
D->BC                                              NO 

By Using key AB we can identify the rest of the attributes (CDEF) of the table. Similarly, Key CD. But, by using key CB we can only identify D and F, not A and E. Similarly key D. 

What is Candidate Key?

A candidate key is a set of attributes (or attributes) that uniquely identify the tuples in relation to or table. As we know the Primary key is a minimal super key, so there is one and only one primary key in any relationship but there is more than one candidate key that can take place. The candidate key’s attributes can contain a NULL value which opposes to the primary key. 

Example :  

Student{ID, First_name, Last_name, Age, Sex, Phone_no} 

Here we can see the two candidate keys ID and {First_name, Last_name, DOB, Phone_no}. So here, there are present more than one candidate keys, which can uniquely identify a tuple in a relation. 

Difference Between Super Key and Candidate Key

Conclusion

A super key is the basic key in a database table. Candidate keys play a main role in identifying the most important key known as the primary key. Super keys provide the foundation for selecting the candidate keys while candidate keys in turn serve as the basis for choosing the primary key of the relation. This relationship between these different types of keys helps establish the structure and organization of the data within the database table.