7 Types Of Keys In DBMS: Best Pathway To Data Control

New to a database and don’t know about the types of keys in DBMS? If yes, then this blog will help you explore the types of keys in DBMS

DBMS stands for Database Management System. It handles data insertions, updates, retrievals, and queries. Some of the most used DBMSs are MySQL, Oracle, Microsoft Access, RDBMS, and many more. DBMS uses keys that are used in a place that defines the relationships among the tables.

Keys are attributes that represent the relationship between the columns of a database. In this blog, you will be clear on the topics related to the keys in DBMS. If you are learning DBMS and struggling with the types of keys in DBMS, then stay tuned with this blog

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What is DBMS?

A database management system (DBMS) is a software application that helps users to create, maintain, and use databases. A DBMS provides a number of features that make it easier to manage databases, including:

  • Data storage and retrieval: A DBMS stores data in a structured format that makes it easy to find and retrieve.
  • Data security: A DBMS can control who has access to data and what they can do with it.
  • Data integrity: A DBMS can be used to ensure that data is accurate and consistent.
  • Data performance: A DBMS can be used to optimize the performance of database queries.

Why Do We Require Different Types of Keys In DBMS?

The different types of keys in DBMS are required for the following reasons:

Uniquely identify rows: A key is a unique identifier for a row in a table. No two rows in a table can have the same key value. This is important for several reasons, including

  • It allows us to find and access specific rows in a table easily.
  • It helps to prevent data duplication.
  • It can be used to enforce referential integrity between tables.

1. Establish Relationships Between Tables

Keys can also be used to establish relationships between tables. A relationship is a connection between two tables with a common data element. For example, a Customer table and an Order table might share a CustomerID column. This column would be a common key between the two tables.

2. Enforce Referential Integrity

Referential integrity is a database constraint that ensures that the values in a foreign key column are also present in the corresponding primary key column. For example, suppose the CustomerID column in the Order table is a foreign key to the CustomerID column in the Customer table. In that case, the CustomerID value in each Order row must also exist in the Customer table.

7 Types Of Keys In DBMS And Their Functions

Following are the types of keys in DBMS and their functions are given below.

Types Of Keys In DBMS #1 – Primary Key

Primary key is one of the most important types of keys in DBMS. There can only be one primary key in a table. The primary key uniquely identifies any record.

Name  Roll__No  Age

Here Roll_No acts as the primary key, as it can be used to identify a particular record. It works as a serial number here, so this kind of primary key is known as the auto-increment primary key. You may wonder if the name column is also a primary key.

There can be two people with the same name, so we cannot use a name as a primary key. The primary key can never be null and duplicated. Also, it cannot be updated or modified if any foreign key refers to it.

Types Of Keys In DBMS #2 –Foreign Key

attribute links two different tables together. It is used for cross-reference. We use a foreign key to main the data integrity. A foreign key refers to the candidate key of a table.                                                                            





The Subject in the Student_info table and Subject in Student_marks are linking two tables. This table shows how both tables are linked together. You will learn about the candidate key in a further section.

Types Of Keys In DBMS #3 –Unique Key

 A unique key is an attribute or a group of attributes that can help you identify a record uniquely. Its included in the another one best types of keys in DBMS. You might be wondering since primary and unique keys both similarly identify a record, aren’t they the same?

Yes, they work in similar ways, but they are different. As we have discussed above, the primary key cannot take null values, but the unique key can accept a null value. Yet you don’t get many options for it, you can only enter a single null value.


In the above table, both Roll_no and Phone_no columns can have unique values. But Phone_no is unique, while Roll_no is primary. This is because it is possible that a student won’t have a phone number, so there we can put null.

Types Of Keys In DBMS #4 – Candidate Key

A candidate key is a group of attributes uniquely identifying a record. The primary key is a part of the candidate key. In simpler words, a candidate key is the group of all the unique keys that can act as a primary key.

Since there can be only one primary key per table, many candidate keys can be possible. One of these candidate keys is a primary key, and the remaining others can be called unique keys. Yet, you cannot add null values to these candidate keys.


Phone and Roll_No columns will have unique and non-null values. But one has to become a primary key and another a candidate key.

Types Of Keys In DBMS #5 – Super Key

A super key is a key used to identify a record from a database uniquely. It is a superset of candidate keys. Including all the possible and potential primary keys. The super key also included in the another one best types of keys in DBMS. It supports null values. All candidate keys are super keys but the reverse is not true.

NameEmp IdPhone

Here Emp Id and Mobile No are both super keys. Both of these columns are potential primary keys. 

Types Of Keys In DBMS #6 –Alternate Key

Since there can be many super keys but only one primary key. The remaining ones are called alternate keys. So we can retrieve and identify any record from the database uniquely using an alternate key too. An alternate key is also a potential primary key of the database.


Here Roll_No acts as a primary key, and Phone is an alternate key. If we had used the Phone as a primary key, then Roll_No could have been an alternate key.

Types Of Keys In DBMS #7 –Composite Key

A group of two or more columns uniquely identifying a record is a composite key. The composite key is not necessarily composed of all unique columns. They together will retrieve and point to a unique record from the database.


In the above table, the Name and Age columns act as a composite key. Name Arya, with Age 21, will be identified in the table. If there is a case with 2 same values in 2 different columns, you can add a third column to your composite key. It is the last one best types of keys in DBMS.

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Functional Dependencies With Various Types Of Keys In DBMS

There are four types of functional dependencies in DBMS:

  • Trivial functional dependency is a functional dependency where the determinant is a subset of the dependent attribute. For example, if we have a table with two attributes, Name and Age, then the functional dependency Name → Age is trivial because Name is a subset of Age.
  • Non-trivial functional dependency is a functional dependency where the determinant is not a subset of the dependent attribute. For example, if we have a table with three attributes, Name, Age, and City, then the functional dependency Name → City is non-trivial because Name is not a subset of City.
  • Multivalued functional dependency is a functional dependency where the value of the dependent attribute can be multiple values for a single value of the determinant. For example, if we have a table with two attributes, Name and Children, then the functional dependency Name → Children is a multivalued functional dependency because a person can have multiple children.
  • Transitive functional dependency is a functional dependency where the value of the dependent attribute is determined by the value of another attribute, which is determined by the value of the determinant. For example, suppose we have a table with three attributes, Name, Department, and Manager. In that case, the functional dependency Department → Manager is a transitive functional dependency because the Department attribute’s value determines the Manager attribute’s value.

Why Do We Need Keys In Dbms

Keys play a crucial role in Database Management Systems (DBMS) for several reasons:

1. Uniqueness

Keys ensure that each record or row in a database table is uniquely identifiable. This uniqueness is essential for accurate data storage and retrieval, preventing duplication and inconsistencies.

2. Data Integrity

Keys help maintain data integrity by preventing the insertion of duplicate records into a table. They ensure that the data remains accurate and reliable over time.

3. Data Retrieval

Keys provide a way to efficiently retrieve specific records from a database. Searching for data using keys is faster than scanning the entire table, especially when dealing with large datasets.

4. Relationships

Keys establish relationships between tables in a relational database. A primary key in one table can be referenced as a foreign key in another, creating links between related data.

5. Joins

In relational databases, keys facilitate the process of joining tables based on common attributes. This allows data from multiple tables to be combined and queried together.

6. Indexing

Keys are often used to create indexes, which improve the speed of data retrieval. Indexes are data structures that help the DBMS locate rows quickly, making queries more efficient.

7. Normalization

Keys are essential in the process of database normalization, which involves organizing data to minimize redundancy and dependency issues. Primary keys are a central component of this normalization process.


Learning about the keys is essential if you learn about DBMS. Keys will help you if you work with databases or are about to work on them. The concept of keys looks complicated and repetitive, but all these keys are related in some way or another.

Follow the blog to clarify all your confusion about all the types of keys in DBMS.

Frequently Asked Questions

Why keys are necessary for DBMS?

Keys are necessary for DBMS because they provide a way to identify each row in a table uniquely. This is important for several reasons, like data integrity, security, and performance.

What is Artificial Key?

An artificial key, also known as a surrogate key, is a unique identifier that is not meaningful to the data. Artificial keys are often used as primary keys when the natural key is not unique or when the natural key is too long or complex.


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