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Concept of Primary Key in DBMS with Example

To build a successful database management system (DBMS), whether you’re a novice or experienced professional, it is vital to comprehend the idea of a primary key. A primary key is a special value which distinguishes each record in a table from all the others and enables data stored in different tables to be connected.


Table of Content


In this article, we’ll explore the definition and importance of primary key in DBMS while demonstrating their usage with an example.


So, let’s get started.

What is the Primary Key in DBMS?

A primary key in DBMS (Database Management System) is a unique identifier or field that ensures data integrity and uniquely identifies each record in a database table. It helps to identify the particular row of data in the table. In other words, it’s a special column or attribute used to identify and link one or more records within a database table. Business Analytics and Data Science professionals use primary keys in DBMS for data integrity, meaning that all rows in a database table are uniquely identified and linked together. 


Concept of Primary Key in DBMS with Example


This helps to make sure no data is inadvertently modified or duplicated. It also ensures that when changes are made, they are always recorded accurately.

Importance of using Primary Key in DBMS

Using a primary key in DBMS design is of utmost importance. Ensuring the integrity, efficiency & effectiveness of the database system is crucial, and it plays a significant role. One key significance of using a primary key is data uniqueness. It helps to identify records uniquely and prevent data redundancy.


Another crucial aspect is efficient data retrieval and manipulation. The database management system can quickly locate and retrieve specific records based on their unique identifiers with a primary key. Furthermore, a primary key is a foundation for establishing relationships between tables in a relational database.

Purpose of Using Primary key in DBMS

A primary key in DBMS is uniquely identifying each record or row within a table. It is a special attribute that ensures data integrity and facilitates efficient data management and retrieval. It also enforces the relationship between two tables in a relational database, providing quick and easy access to related data. In addition, primary keys in DBMS are used to optimize query performance by enabling faster data indexing.


Primary keys are essential for database design because they guarantee that no two records contain the same information, making them an invaluable tool for maintaining data integrity over time. With a primary key, it would be easier to identify each record accurately when performing searches or making updates.

How Primary Key in DBMS Works?

A primary key is a distinct label assigned to every entry in a table within a database. It’s used to uniquely identify each row or record to easily retrieve, update, or delete. Primary keys must have unique values and cannot contain null values.


The primary key in DBMS, such as MySQL and Oracle, is typically an auto-incrementing integer. This means the database automatically assigns a new number every time you create a new record, ensuring each row has its unique identifier.


Primary keys are also often referred to as “candidate keys” since they are used to locate records within the database quickly and accurately. This makes them important for maintaining data integrity and reducing redundancy in large datasets.


Moreover, keys in DBMS are important because they provide relationships between tables.

Comparison with other Key Types

Let’s deep dive and see the comparison of keys in DBMS in detail:


Key Type Uniqueness Null Values Relationship Purpose
Primary Key Unique Not Allowed Establishes Relationships  Uniquely identifies each record, maintains data integrity
Foreign Key Not Necessarily Unique Allowed Establishes Relationships referential integrity
Unique Key Unique Allowed Not Applicable Ensures uniqueness of attribute(s) other than the primary key
Candidate Key Unique Allowed Not Applicable A potential primary key, a minimal set of attributes that uniquely identifies each record

Characteristics of Primary Key in DBMS

Here are the key characteristics of primary key in DBMS:


  • Uniqueness: A primary key must ensure the uniqueness of each value within a table. No two records could have the same value for the primary key attribute.
  • Non-nullability: A primary key must have non-null values. This means that the primary key attribute for each record cannot be empty or null. This constraint ensures that the primary key serves as a reliable identifier for every record in the table.
  • Stability: The values of a primary key should ideally remain stable over time. It means that once a value is assigned as a primary key for a record, it should only change if necessary. This stability helps maintain consistency and reliability in data relationships and references.
  • Minimal: A primary key, consisting of the smallest set of attributes necessary to identify each record uniquely, should be minimal. This helps optimize storage space and improve query performance by reducing the index size or data structure associated with the primary key.
  • Easily accessible: The primary key should be easily accessible, allowing efficient data retrieval and manipulation. It is a key reference point for locating specific records within the table or establishing relationships with other tables. By providing quick and direct access, it enhances the performance and usability of the database system.

Importance of Choosing the Right Attributes 

Here’s why choosing the right attributes is crucial:


  • Efficient Data Storage

    Selecting the right attributes allows for efficient data storage. Identifying and including only the necessary attributes minimises unnecessary overhead and storage space.

  • Accurate Representation of Data

    Choosing the right attributes ensures that data is accurately represented within the data structure. Each attribute should capture relevant information crucial for the data structure’s intended purpose.

  • Effective Data Retrieval

    The choice of attributes greatly affects the efficiency of data retrieval operations. Data retrieval becomes faster and more precise by including attributes that are frequently accessed or used for filtering and sorting.

  • Data Integrity and Consistency

    The right attributes contribute to data integrity and consistency. Including attributes that enforce constraints, such as unique or non-null values, helps maintain data integrity by preventing duplicate or inconsistent data entries.

  • Scalability and Adaptability

    Choosing the right attributes allows for scalability and adaptability of the data structure. By considering future needs and potential changes, attributes can be selected to accommodate evolving requirements.

  • Efficient Data Processing

    The selection of appropriate attributes influences the efficiency of data processing operations. The data processing becomes more streamlined by including attributes relevant to the desired data operations, such as filtering, aggregating, or sorting.

Example of Primary Key in DBMS

Consider a table called “Students” that stores information about students in a school. Let’s assume we have the following attributes: StudentID, Name, Age, and Grade. In this example, we will designate the “StudentID” as the primary key.


StudentID Name Age Grade
001 John Smith 17 11
002 Emily Davis 16 10
003 Mark Johnson 18 12
004 Sarah Lee 15 9


In the table above, each row represents a student record. The “StudentID” column serves as the primary key, uniquely identifying each student in the table. No two students can have the same “StudentID” value.


For example, the first row shows that “John Smith” has a StudentID of “001”. This ID is unique to him and allows us to specifically identify and retrieve his information from the “Students” table.


The primary key in DBMS plays a crucial role in maintaining data integrity, ensuring that each student’s record is unique and identifiable within the table. It allows for efficient retrieval, manipulation, and referencing of data in the database management system.

How to Create a Primary Key in DBMS Table

To create a primary key in DBMS table, follow these steps:


  • Determine which attribute or combination will uniquely identify each record in the table. This attribute(s) will become the primary key.
  • When creating the table, specify the chosen attribute(s) as the primary key. You can do this in the table creation statement or by altering the existing table structure.
  • If you’re creating the table from scratch, include the primary key declaration within the table creation statement. For example, you can use the “CREATE TABLE” statement with the “PRIMARY KEY” constraint in SQL.
  • If the table already exists, you can alter the table structure to add the primary key constraint. Use “ALTER TABLE” statement to modify the table and add the primary key constraint to the desired attribute(s).
  • Ensure that each record has unique values for the chosen primary key attribute(s). If any records violate this uniqueness constraint, you may need to modify the data or choose a different primary key.
  • Consider additional options related to the primary key, such as whether it can contain null values or if it should be auto-incremented (if supported by the database system).


Benefits of Primary Key in DBMS

Here are the benefits of using a primary key in a DBMS:


  1. A primary key ensures that each record in a table has a unique identifier.
  2. By enforcing uniqueness, a primary key helps maintain data integrity.
  3. The primary key is a reliable and efficient means of identifying specific records in a table.
  4. A primary key in establishing relationships between tables in a relational database is vital.
  5. The primary key is typically used as an index in database systems, facilitating faster data retrieval.
  6. A primary key simplifies updates to existing records.


Read about – Application of data structure

Importance of using the primary key in large, complex database systems

The risk of data duplication or inconsistency is higher in large, complex database systems. Using a primary key ensures the uniqueness of each record, maintaining data integrity throughout the system.


Large database systems often contain millions or even billions of records. In such cases, efficient data retrieval becomes paramount.


Complex database systems usually involve multiple tables with intricate relationships. The primary key is a reference point for establishing these relationships, and maintaining referential integrity.


In large-scale systems, optimizing database performance is crucial. The primary key plays a vital role in this optimization process.


Read about – Types of Data Structure

The Bottom Line

In this guide we have covered everything related to primary key in DBMS. A primary key is an important concept in Database Management Systems. It ensures that each row of data within the database table has a unique identifier which helps maintain the data’s integrity. It ensures that no duplicate records are created and that records can be accurately identified and located when needed. 


An example of a primary key will be an ID assigned to each customer in a customer database table which could then be used to identify individual customers and their associated information. This makes it easier to manage and analyze data within the database.


A primary key in database is a unique identifier for each record or row, which can help retrieve data from the table. It ensures that no two records have the same value and helps maintain the data's integrity.
The main purpose of using a primary key in database is to identify each record or row within a table uniquely. It helps ensure that the data stored in the table remains consistent and reliable, as no two records can ever have the same value for their primary keys.
Primary keys are essential in relational databases as they help to maintain data integrity and enforce relationships between tables. Having one designated field to identify each row in a table uniquely makes creating and maintaining relationships between different tables easier. Data can become inconsistent and corrupt without primary keys due to duplicate entries or inaccurate references between tables.
Generally, the best practice for choosing a primary key is to use a single field that contains a unique value for each record. The ideal data type could be an integer or auto-incrementing number, but it can also be something like a customer ID or name if those fields contain unique values across all records.

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