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9 January 2023

Difference Between Super Key and Candidate Key

A super is a set of attributes in a relation that uniquely identifies a record. It can be a combination of one or more attributes in the relation. A candidate key is a minimal set of attributes that can uniquely identify a record. It is a subset of a super key and contains only the attributes that are necessary to uniquely identify a record. 

A record in a table can be uniquely identified using either a super key or a candidate key. Furthermore, the relationship between tables is established using these keys. Both keys are open to having null values. Both ideas are crucial for database administration and design. Learn more about super keys and candidate keys in this post, as well as how they differ from one another. Let us discuss some more differences between Super Key and Candidate Key with the help of the comparison given below.

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What is Super key?

A super key is a single attribute (or combination of attributes) that is used in a relational database to uniquely identify each attribute in a relation. Even though each one of these properties is adequate to uniquely identify a student, a super key for a student's database may include the attributes roll number and student ID. A super key is a fundamental relational key that can identify any relational characteristics. Every connection must contain one or more super keys, preferably more. 

What is the Candidate key?

A candidate key may be used in conjunction with a primary key to uniquely identify records in a table. The potential key column may be empty. There may or may not be a main key for a candidate key. A candidate key is essentially a subset of a super key. A tuple in a table may be uniquely identified using a bare minimum amount of properties. All potential keys are therefore super keys. Because only one of these qualities may be used to uniquely identify a student, the candidate key for a student database, for instance, would only include one attribute, such as roll number or student ID. 

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Difference between super key and candidate key:

  • A super key is an attribute(or set of attributes) that is used to uniquely identify all attributes in a relation. A super key's subset is known as a candidate key.
  • All super keys can't be candidate keys. But all candidate keys are super keys.
  • The super key is various keys that together make the criteria to select the candidate keys. While various candidate keys together make the criteria to select the primary keys. 
  • In relation, the number of super keys is more than the number of candidate keys. While in relation, the number of candidate keys is less than the number of super keys.
  • Super key attributes can contain NULL values. NULL values can also be assigned to candidate key attributes.
  • A combination of characteristics or columns known as a super key uniquely identifies each row in a table. While in candidate key is a set of attributes that recognize the tuples in relation or table.
  • The number of super keys is greater than the number of candidate keys. In comparison to super keys, there are fewer candidate keys.
  • The rules for selecting the primary keys are made up of a variety of candidate keys. In the candidate key numerous super keys collectively make the guidelines to choose the candidate keys.
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