What is super key in SQL with example?

A super key is a superset of a candidate key. For example: In the above EMPLOYEE table, for(EMPLOEE_ID, EMPLOYEE_NAME), the name of two employees can be the same, but their EMPLYEE_ID can’t be the same. Hence, this combination can also be a key. The super key would be EMPLOYEE-ID (EMPLOYEE_ID, EMPLOYEE-NAME), etc.

How do you write a super key?

Examples of superkeys are as follows: Name+SSN+Birthdate. ID+Name+SSN….As an example, a table used to store customer master details could contain columns such as:

  1. Customer name.
  2. Customer ID.
  3. Social Security number (SSN)
  4. Address.
  5. Date of birth.

Is super key same as primary key?

Difference between Super Key and Primary Key: Super Key is an attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation. Primary Key is a minimal set of attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation.

How do I find my Superkey and candidate key?

Candidate Key is a Super Key whose no proper subset is a super key, i.e. suppose if ABC is a candidate key then neither A, B, C or any of its combination can be super key, hence we can say candidate key is a minimal set of attributes of an R( Relational Schema) which can be used to identify a tuple of a table uniquely.

How many Super keys are possible?

The possible number of superkeys is 2(n-k).

What are Superkeys in relation?

In the relational data model a superkey is a set of attributes that uniquely identifies each tuple of a relation. Because superkey values are unique, tuples with the same superkey value must also have the same non-key attribute values. That is, non-key attributes are functionally dependent on the superkey.

Is super key a candidate key?

Every super key cannot be a candidate key. All candidate keys are super keys.

What is meant by super key?

How do I find my superkey and candidate key?

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.

Can Super key be unique?

Because superkey values are unique, tuples with the same superkey value must also have the same non-key attribute values. That is, non-key attributes are functionally dependent on the superkey.