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Why is a candidate key called a minimal super key?

Key: A field or group of fields in a table that uniquely identifies a record (row) is a key in database management systems (DBMS). Data integrity, indexing, and creating connections between tables all depend on keys. They are essential for effectively organizing and retrieving data.

Candidate Key: A collection of one or more fields known as a candidate key can uniquely identify each record in a database. Although it satisfies the criteria for a main key, it might have yet to be chosen as the primary key. One of several potential candidate keys for a table is ultimately picked as the primary key.

  • A candidate key is an attribute or a group of attributes uniquely identifying a tuple.
  • The candidate key
  • s are a different collection of properties from which the primary key might be chosen.
  • NULL values are permitted for candidate keys.
  • A candidate key is a super key with the fewest possible properties.

Why Candidate key is called Minimal super Key:

Regarding database management systems, a minimum super key is a super key that cannot be further condensed while still having the ability to identify each record (row) in a table uniquely. It is the tiniest collection of characteristics (columns) that can serve as a super key.

Let's first go over what a super key is to comprehend the idea of a minimum super key. Each tuple (row) in a table can be uniquely identified by a collection of one or more properties known as a super key. Although it may have other properties that are not essential for uniquely identifying the data, it assures the uniqueness of records in a table.

Each record in a database can be uniquely identified by a candidate key, a grouping of one or more fields. It may have yet to be picked as the major key, even if it meets the requirements for a main key. The main key for a table is finally chosen from among several probable candidate keys.

Think of a table of workers that includes information about them, like their name, department, email address, and employee ID. Employee ID and email can be a super key for this table since they ensure each employee is unique. But uniqueness is not contingent on the name and department properties. Being the lowest collection of attributes that may be used to uniquely identify each employee, the combination of employee ID and email is a minimum super key.

A candidate key is known as a minimal super key because we choose it from a group of super keys so that it is the bare minimum characteristic necessary to distinguish the table from others.

A set of one or more qualities (columns) that may uniquely identify each tuple (row) in a database table is known as a super key. In other words, a super key ensures that each entry in a database is unique. However, a super key could have extraneous characteristics that are unnecessary for uniqueness.

A candidate key, on the other hand, is a minimum super key. It is a super key that lacks any extra properties. A candidate key is the smallest collection of properties that may be used to identify each tuple in a table in a certain way. Any attribute would lose its uniqueness if removed from a candidate key.

When referring to candidate keys, the word "minimal" means that no subset of a candidate key can be used to identify tuples in the database in a singular way. A candidate key is minimum because it cannot be further decreased without losing uniqueness.


Consider the Student table with attributes student_id, Name, Email, and phone_number.

student_id Name Email Phone_number
1 A [email protected] 123
2 B [email protected] 456
3 C [email protected] 789
4 D [email protected] 112

We will examine each attribute's uniqueness in this table to determine the potential keys.

Key candidate number one: student_id

Each student has been given a special student_id.

Each student in the table is identified specifically by their student_id.

The student_id distinctiveness would be lost if it were removed.

Email is the second possible key. Every student has a different email address.

Each student in the table is identified just by their email.

The Email would lose its individuality if it were removed.

Each student in the "Students" database may be uniquely identified using either Candidate Key 1 (Student_id) or Candidate Key 2 (email), which can both act as minimum super keys. The uniqueness of these keys would be lost if any attribute were to be removed.

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