Types of Keys In DBMS

7 Must-Know Types of Keys in DBMS 2023 Edition

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


What Is DBMS?

DBMS stands for Database Management System. It is a software system designed to manage, organize, store, and retrieve data efficiently and securely. DBMS software acts as an interface between users and the database, allowing users to interact with the database without knowing the underlying details of how the data is stored.

Examples of DBMS

Some common examples of DBMS include MySQL, Oracle, Microsoft SQL Server, and PostgreSQL. DBMS is used in various applications, from small personal databases to large enterprise systems that store critical business data. It helps ensure the integrity, security, and consistency of the data stored in the database and provides users with tools to search, sort, and analyze it.

Purpose of Using Keys in DBMS

We use keys to open or pick a particular lock, the same way keys work in DBMS. You can retrieve and identify any unique column or row from the table in the database.

Getting a record from a single table is easy, as compared to when you have to find a record from a complete database. There can be hundreds of records in a table in the database. The concept of keys is very helpful in these kinds of situations.

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There are 7 keys in DBMS: Primary key, candidate key, alternate key, super key, foreign key, unique key, and composite key. You will read about these types of keys in DBMS with all the details in the next paragraph.

7 Types Of Keys In DBMS And Their Functions

1. Primary Key

Primary key is one of the most important keys used in the 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.

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.

3. Unique Key

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

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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.

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.

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. 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. 

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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.

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.

DBMS Projects Ideas

Here are some project Ideas for DBMS projects:

  1. E-commerce Website
  2. Inventory Management System
  3. Movie Rental System
  4. Hospital Management System
  5. Social Media Platform
  6. Online Library Management System
  7. Employee Attendance System
  8. Online Banking System
  9. Student Information System
  10. Online Voting System
  11. Travel Reservation System
  12. Online Job Portal
  13. Restaurant Management System
  14. Online Examination System
  15. Customer Relationship Management System (CRM)
  16. Online Auction System
  17. Music Streaming Platform
  18. Online Ticket Booking System
  19. Order Management System
  20. Online Hotel Booking System


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

What are the types of DBMS?

There are four major types of DBMS (DataBase Management Systems). 
Relational database.
Object-oriented database.
Hierarchical database.
Network database.

Can we use DBMS in real life?

Yes, we can use DBMS in real life to store the monthly postpaid bills and call details. All transactions and purchases of items with credit cards are only possible with DBMS. Security and privacy of all the transaction information are only possible with the help of Database Management systems. 


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