Difference between Super Keys and Candidate Key in SQL

Table of Content
What are the Keys in DBMS?
How do Superkeys work?
Properties Of Superkey
What is a Candidate Key?
Properties of a Candidate key
Super key Vs Candidate key

Rows and columns exist in relational databases, as is well known. The names of the columns vary, such as Aadhar Number, Roll No., Marks, etc. So, selecting the column with the specified name will make it simple for us to get the data in a specific column. But what if we only need to access a specific table row? How can we access a certain row if it has no unique name? Therefore, we must be able to uniquely identify each database row using some property, attribute, or method. This is where keys come into play.

In SQL and databases, we employ a variety of keys, including Primary, Unique, Foreign, Super, Alternate, Composite, and others.

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However, we shall discuss the distinction between Candidate Key and Superkey Key in this article. Let's first discuss keys in the database before moving on to the differences.

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What are the Keys in DBMS?

Every relational database must contain keys. In a DBMS, a key is an attribute, or group of characteristics, that makes it easier to identify individual tuples within a table. Additionally, additional integrity requirements are defined and relationships between various database tables are established using keys. A relational database table represents a collection of records or events of a specific relation. There could be hundreds and hundreds of these records at this point, some of which might be duplicates. Since there shouldn't be any duplicate records, it should be possible to identify each record separately. The keys enable us to be rid of this issue as well.


How do Superkeys work?

In a relational database, a row or tuple can be uniquely identified by one or more properties, known as a superkey.

OR

An attribute or group of attributes that may be used to uniquely identify all other attributes is known as a super key.


Properties Of Superkey

• It gives each row in a table a distinct identity.
• The table may contain more than one superkey.
• It can be created with a single column or several columns.
• It serves as the foundation for choosing a candidate key.

What is a Candidate Key?

The superkey in question is referred to as a candidate key whose suitable subset does not include any superkeys. It essentially represents the superkey in its most basic form. A table may include just one candidate key or it may contain several candidate keys. The relational table we are using determines how many candidate keys there are.


Properties of a Candidate key

• It only has distinct values.
• It gives each row in a table a distinct identity.
• It might have several characteristics.
• To ensure uniqueness, it has the bare minimum of fields.

 

Super key Vs Candidate key
 

Sr.No	Super Key	Candidate Key
1.	A Superkey is a single attribute or a set of attributes that can uniquely identify a row/tuple in a relational database.	That superkey is said to be a candidate key whose any of the proper subsets is not a superkey in itself. It is basically the minimal version of the super key.
2.	Every Candidate Key is a Super Key.	Every Super Key is not a Candidate Key.
3.	A set of all the Super Keys together makes the criteria to select the candidate keys.	Various candidate keys together make the criteria to select the primary keys.
4.	There are comparatively more Super Keys in the relational table.	There are comparatively fewer candidate keys in the relational table.

 

 

Is a super key also a candidate key?

A subset of a super key is called a candidate key. Candidates' keys cannot all be super keys. However, every candidate key is a super key.

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