Super Key vs. Candidate Key: What's the Difference?
Edited by Aimie Carlson || By Janet White || Published on February 19, 2024
Super key in a database is a set of one or more columns that can uniquely identify a record; candidate key is a minimal super key without redundant attributes.
Key Differences
A super key in a database is a set of one or more attributes (columns) that, taken together, can uniquely identify a record in a table. A candidate key is a specific type of super key; it is the minimal set of attributes necessary to uniquely identify a record, with no extraneous data.
Super keys can include additional attributes that are not necessary for unique identification. In contrast, candidate keys are stripped down to the bare minimum number of attributes required to maintain uniqueness in the identification of a record.
Any candidate key can be considered a super key, but not all super keys are candidate keys. This is because super keys may contain additional attributes that aren't essential for uniqueness, which is not the case with candidate keys.
When defining a database schema, super keys can be identified first, which may include a range of attributes. Candidate keys are then derived by reducing these super keys to their simplest form, ensuring they have just enough attributes to uniquely identify records.
In a practical database, candidate keys are often the focus since they provide the most efficient way of identifying records without redundancy. Super keys, while important conceptually, are often too broad and contain unnecessary information for unique record identification.
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Comparison Chart
Definition
A set of attributes that can uniquely identify a record
A minimal super key with no redundant attributes
Redundancy
Can have redundant attributes
No redundant attributes
Uniqueness
Ensures record uniqueness
Ensures record uniqueness in the simplest form
Simplicity
Not necessarily minimal
Always minimal
Role in Databases
Conceptual, identifying possible unique identifiers
Practical, used as primary keys or unique constraints
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Super Key and Candidate Key Definitions
Super Key
A super key is a combination of attributes that can uniquely identify a table record.
In a student database, a combination of student ID and name can be a super key.
Candidate Key
In database management, a candidate key is the smallest possible group of attributes that can uniquely identify a database entry.
StudentID can be a candidate key in a university course enrollment table.
Super Key
Super key refers to a set of attributes in a database table that can uniquely identify each record.
A super key in a book database might include {ISBN, Title, Author}.
Candidate Key
Candidate key in a database is the simplest combination of columns that can uniquely identify a table record.
EmployeeID could be a candidate key in an employee table.
Super Key
In database management, a super key is a collection of one or more attributes that can uniquely identify a database entry.
{StudentID, CourseID, Semester} can act as a super key in a university course enrollment table.
Candidate Key
Candidate key refers to a minimal set of fields that can uniquely identify each record in a database table.
ISBN could be a candidate key in a book database.
Super Key
Super key in a database is any group of columns that can be uniquely used to identify a record.
{EmployeeID, EmployeeName, Department} could be a super key in an employee table.
Candidate Key
A candidate key is a minimal set of attributes necessary to uniquely identify a record in a table.
In a student database, StudentID alone could be a candidate key.
Super Key
A super key is a set of one or more columns that, together, ensure the uniqueness of each row in a table.
In a vehicle registration database, {LicensePlate, VIN} forms a super key.
Candidate Key
A candidate key is a set of attributes that are minimal and sufficient to uniquely identify a row in a table.
In a vehicle registration database, LicensePlate alone might be a candidate key.
FAQs
Can a super key become a candidate key?
A super key can be a candidate key if it's the minimal set required for uniqueness.
What is a super key?
A super key is a set of one or more attributes that can uniquely identify a record in a table.
Can a table have more than one candidate key?
Yes, a table can have multiple candidate keys.
Are all candidate keys also super keys?
Yes, all candidate keys are a form of super key.
Is a primary key a candidate key?
Yes, a primary key is a special case of candidate key chosen to uniquely identify records.
Can a candidate key have multiple attributes?
Yes, if multiple attributes are needed to ensure uniqueness.
What makes a candidate key different from a super key?
A candidate key is a minimal super key, containing no redundant attributes.
Is it necessary for a super key to be minimal?
No, minimality is not a requirement for super keys.
Do super keys include primary keys?
Yes, primary keys are a type of super key.
How is a candidate key chosen from super keys?
By eliminating redundant attributes to achieve minimal attribute sets.
What is the role of candidate keys in database normalization?
They help achieve normalization by ensuring data uniqueness and integrity.
Is it possible for two tables to have the same candidate key?
Yes, especially if they are related or have similar data structures.
Are candidate keys always used in databases?
Yes, they're crucial for identifying records uniquely.
Can a super key contain non-key attributes?
Yes, a super key can include non-key attributes.
How are candidate keys identified?
By analyzing data requirements and ensuring minimal attribute sets for uniqueness.
Do all super keys ensure uniqueness in a table?
Yes, all super keys ensure record uniqueness.
Can foreign keys be candidate keys?
Yes, if they uniquely identify records in their own table.
Do candidate keys change over time?
They can, if the data structure or requirements of the database change.
How many candidate keys can a table have?
There's no limit to the number of candidate keys a table can have.
Are super keys used in creating database indexes?
Yes, super keys can be used for indexing, but candidate keys are more efficient.
About Author
Written by
Janet WhiteJanet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie CarlsonAimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.
