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Table of contents
Examples Of Super Key in DBMS
Role Of A Super Key
How to find Super Keys in DBMS?
Real-life use case scenario of Super keys in DBMS
Difference between Candidate Key and Super Keys
Uses of Super Keys in DBMS
Importance of Super Key
Frequently Asked Questions
What is the super key formula in DBMS?
Can super key have duplicate values?
How many super keys are possible?
Can a relation have multiple super keys?
Last Updated: Jul 17, 2024

What is Super Keys in DBMS?

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Prerita Agarwal
Data Specialist @
23 Jul, 2024 @ 01:30 PM

Super keys in Database management software refer to one or more attributes that can be used to identify a specific record or tuple in a database uniquely. The super key is essential when searching for a single record within the database or table. 

Super keys in Database management

There are many cases where you use super keys in a DBMS, and there are some specific criteria that an attribute must specify to use them as a super key. We will also discuss why super keys are so critical in modern databases. Let us look at the Super keys in further detail in this article.

But before we start, you must know about - keys in DBMS

In the context of database management systems (DBMS), a super key is a set of one or more attributes (columns) that uniquely identifies a record or tuple in a database table. It's called a "super" key because it has the ability to uniquely identify records, but it may contain more attributes than what is necessary for this purpose.

Also see - Locked based protocol in DBMS

Examples Of Super Key in DBMS

If we have a student table with attributes first name, last name, roll number, section: 

  • Now if you take the combination of attributes first name, and last name, the combination cannot help us get a single student because there can be multiple students with the same first and last name.
  • This is where Super keys reduce the number of possible combinations that we need to consider. Super keys are the superset of all candidate keys.
  • Because there is at least one attribute in Super keys that can uniquely identify any record from the table, we can use them to consider making our candidate keys and then further the Primary keys.

Let us now see how we can find the super key in a table. 

Also read, File System vs DBMS

Role Of A Super Key

This refers to the set of all possible keys that we can use to identify a particular record in the database uniquely. In Super keys, we can have redundant attributes as well, but having an attribute that can uniquely identify the records is necessary.

A super key in a database is a set of one or more attributes that uniquely identify a tuple (row) within a relation (table). The primary role of a super key is to ensure entity integrity by preventing duplicate rows in a table, thus maintaining data accuracy and consistency. It includes candidate keys (minimal super keys) and can have additional attributes beyond what is necessary for unique identification. Super keys help in defining primary keys and enforcing uniqueness constraints, which are crucial for indexing, optimizing queries, and maintaining referential integrity in relational databases.

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How to find Super Keys in DBMS?

Finding super keys in a database involves identifying combinations of attributes that uniquely identify each record in a table. 

How to find Super Keys in DBMS?

Step 1: Start by examining the attributes (columns) of the table. Let's say we have attributes A, B, C, and D.

Step 2: Take a single attribute and consider it as a potential super key on its own. Check if it can uniquely identify each record. If it does, then that attribute alone is a super key. In our example, if attribute A uniquely identifies each record, then A is a super key.

Step 3: Now that if A is a super key, then the combination of other attributes with A will also be considered as a super key. 

Step 4: If a single attribute does not uniquely identify records, consider combinations of two attributes. Take any two attributes and check if their combination can uniquely identify each record. If it does, then that combination is a super key. 

For example, if the combination of attributes A and B uniquely identifies records, then (A, B) is a super key.

Step 5: Repeat step 3 with combinations of three attributes, then four attributes, and so on, until you have considered all possible combinations of attributes.

Step 6: Each combination of attributes that uniquely identifies records is a super key.


To better understand the steps to find the Super Keys in a table, let's take a simple example:

Consider a table about the data of students that contains the student_idnameage, and email_id

  • Now according to step 1 the attributes of the table are student_idnameage, and email_id.
  • In Step 2 we examine if any single attribute qualifies as a super key, which gives us that student_id and email_id individually can be made super keys.
  • Now in Step 3 we make the different combinations of the two attributes with the other redundant attributes. 
  • We keep different combinations possible in Step 4 that can be possible super keys and be used for unique identification of students in the table. 
  • The super keys are:{student_id, email id, student_id email_id, student_id name, student_id age,...}. 

Real-life use case scenario of Super keys in DBMS

We can see the usage of super keys in modern DBMS concepts by taking the example of a real-life database:

Let's take the example of a data table on an e-commerce website that stores the data of the orders made by various users

222023-05-01Product A
232023-05-03Product B
242023-05-05Product C
  • Now the attributes of this table are order id, order date, and the product.
    Now whenever any user searches for their order on the website, what is essentially happening in the background is that we are searching for a single product in the order table.
  • This is where we realize the significance of super keys; here, we take the super key to be the combination of order id and order date, so we can search for a single product in the orders table easily. 
  • This reduces the time and complexity of searching for particular orders inside the table.

Difference between Candidate Key and Super Keys

Having come so far in the article, you can see that candidate and super keys are closely related; let us now look at the points of difference between them:

Difference between Candidate and Super Keys

ParametersCandidate KeySuper Key
UniquenessUniquely identifies each tuple without redundancy.It can uniquely identify tuples but may have redundancy.
RedundancyDoes not contain any redundant attributes.It may contain redundant attributes.
Attribute setMinimal set of attributes that ensure uniqueness.It may contain additional attributes that are not required for the unique identification of records.
QuantityThere can be multiple candidate keys for a table.There are many combinations of attributes possible, so there are many super keys possible for a table.
Primary Key sectionWe use the set of all candidate keys to select the primary key for the table.We use the set of Super keys to make the set of Candidate keys, but they don't have any direct association with primary keys.

Let us now see the uses of Super Keys in DBMS: 

Uses of Super Keys in DBMS

Now let's see the various uses of Super keys in DBMS briefly:

  • As we discussed above, Super keys help in maintaining the uniqueness of records and data integrity, and they help in easy searching for unique records in the table.
  • The set of Super keys is essential because they help in selecting the candidate keys and then the primary keys for the table.
  • As we have seen, the search time reduces when we use proper super keys, so they help in the overall performance optimization regarding data retrieval.
  • Super keys are also useful when we want to establish relationships and connect two tables.

Importance of Super Key

In database management systems (DBMS), a super key is a set of one or more attributes that, taken collectively, can uniquely identify a record in a table. The importance of a super key lies in its role in defining candidate keys and, ultimately, the selection of a primary key. Here are key points regarding the importance of super keys in DBMS:

  • Uniqueness Identification: A super key ensures that each record in a table can be uniquely identified. This is crucial for maintaining data integrity and avoiding duplication.
  • Candidate Key Formation: A super key serves as the basis for identifying candidate keys. Candidate keys are minimal super keys, meaning that no proper subset of a candidate key is also a super key. The process of selecting a primary key often involves choosing one candidate key from the set of super keys.
  • Primary Key Selection: The primary key is a special candidate key chosen to uniquely identify records in a table. Super keys play a vital role in the identification and definition of candidate keys, from which the primary key is selected. The primary key is used as a unique identifier and for establishing relationships between tables.
  • Database Normalization: Super keys are essential in the normalization process, which involves organizing a database to minimize redundancy and dependency. By identifying and using super keys, one can optimize the database structure to improve efficiency and reduce data anomalies.
  • Query Optimization: The proper use of super keys, candidate keys, and primary keys can contribute to the optimization of database queries. Indexing is often based on primary keys, which allows for faster retrieval of data.

Also read anomalies in database

Also read, Aggregation in DBMS

Frequently Asked Questions

What is the super key formula in DBMS?

A super key is any set of attributes that uniquely identifies a record. The formula is Super Key = {Attributes}, where Attributes is a set of one or more attributes.

Can super key have duplicate values?

No, a super key cannot have duplicate values within a single relation (table). Its primary role is to uniquely identify tuples, so duplicate values would violate the integrity constraint and defeat the purpose of a super key.

How many super keys are possible?

The number of possible super keys in a relation (table) is exponential, determined by the number of attributes in the relation. It is calculated as 2^n, where n is the number of attributes in the relation.

Can a relation have multiple super keys?

Yes, a relation (table) can have multiple super keys. Each super key uniquely identifies tuples within the relation, and there can be several combinations of attributes that satisfy this criterion, resulting in multiple super keys for the same relation.


After going through this article, you should be able to see how essential Super keys are in modern databases. You were able to see how we use Super keys to search for particular records in a Database and what are the possible number of possible super keys when we have the table.

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