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In the world of relational databases, understanding the difference between primary key and foreign key is essential. This is because primary keys and foreign keys are two very important components of any database, as they help define the structure of a database as well as maintain data integrity.
The key differences between the primary key and foreign key is that, the primary key is about uniquely identifying records within a table, while the foreign key establishes relationships between tables and enables the linking of data across multiple tables. Both keys play crucial roles in maintaining data integrity, consistency, and relational structure in a database.
In the section below, we’ll discover more differences between the primary key vs foreign key in detail.
So, let’s get started.
Before knowing the difference between primary key vs foreign key, let’s understand what they mean. A primary key is a special attribute or field within a database table that uniquely identifies each record or row in that table. It acts as a distinctive label for every information stored in the table, ensuring that no two records have the same identifier. This unique identification helps locate, access, and manipulate specific data within the table.
Primary keys are used for a variety of purposes, including maintaining data integrity and integrity constraints, ensuring efficient record lookup, forming relationships between different tables in a database, and providing an effective way to ensure the uniqueness of records. The business analytics course will teach you just how important having a primary key in your database is.
Let’s understand the difference between primary key and foreign key with the help of examples:
Employee ID | First Name | Last Name | Department |
001 | John | Smith | Sales |
002 | Emily | Johnson | HR |
003 | Michael | Williams | Marketing |
004 | Sarah | Davis | Operations |
In this example, the “Employee ID” column is the primary key for the “Employees” table. Each employee has a unique ID assigned to them, ensuring that no two employees share the same ID. The primary key column uniquely identifies each record within the table, allowing for easy access and manipulation of specific employee data.
Most of the primary keys in DBMS are numerical, but they can also be text data or a combination of both. Read on & learn about the difference between primary key and foreign key.
Before knowing the difference between primary key vs foreign key, let’s understand what they mean. A foreign key is a relational database theory that connects and establishes relationships among different tables by referring to the primary key of another table. This linking enables sharing and exchanging data between the two tables. The purpose of using foreign keys is to enforce referential integrity and maintain data consistency across tables. It ensures that the values stored in the foreign key field of one table are also present in the primary key field of another table.
A foreign key is usually composed of multiple columns used to identify a row in the related table uniquely. The number of columns used depends on how many columns make up the primary key in the related table.
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Let’s understand the difference between primary key and foreign key with the help of examples:
Here’s an example of two tables, “Students” and “Courses,” with a foreign key relationship explained. Consider a table named “Students” that stores information about students and another table named “Courses” that stores information about different courses offered. Let’s establish a relationship between these two tables using foreign keys. Below, we’ll look at the difference between primary key and foreign key.
Table: Students
Student ID | First Name | Last Name | Age | Grade |
001 | John | Smith | 18 | A |
002 | Emily | Johnson | 19 | B |
003 | Michael | Williams | 20 | A |
Table: Courses
Course ID | Course Name | Instructor |
101 | Mathematics | Prof. Anderson |
102 | English | Prof. Thompson |
103 | Science | Prof. Parker |
To establish a relationship between these tables, we can introduce a foreign key in the “Students” table that references the primary key of the “Courses” table. Let’s add a column called “Course ID” as a foreign key in the “Students” table.
Table: Students
Student ID | First Name | Last Name | Age | Grade | Course ID |
001 | John | Smith | 18 | A | 101 |
002 | Emily | Johnson | 19 | B | 102 |
003 | Michael | Williams | 20 | A | 103 |
Let’s deep dive and understand the major difference between Primary Key and Foreign Key in detail:
Basis | Primary Key | Foreign Key |
Definition | A primary key is a unique identifier for each record in a table. | A foreign key establishes a relationship between tables by referencing the primary key of another table. |
Basic | Ensures uniqueness and data integrity within a single table. | Establishes relationships and maintains referential integrity between tables. |
NULL | Does not allow NULL values in the primary key field. | Allows NULL values in the foreign key field, indicating a missing or unspecified relationship. |
Count | Only one primary key can exist per table. | Multiple foreign keys can exist within a table, depending on the relationships with other tables. |
Duplication | No duplicate primary key values are allowed within the table. | Can contain duplicate foreign key values, reflecting multiple records associated with the same reference. |
Indexing | Primary keys are automatically indexed to enhance data retrieval speed. | Foreign keys can be indexed but are not automatically indexed. |
Deletion | Deleting a record with a primary key constraint can affect referential integrity in related tables. | Deleting a record with a foreign key constraint can be restricted or cascade to maintain integrity. |
Insertion | Each new record must have a unique primary key value assigned. | The foreign key can reference an existing primary key value or be NULL if the relationship is optional. |
Temporary table | Primary keys can be applied to temporary tables. | Foreign keys can also be applied to temporary tables to establish relationships. |
Relationship | Primary keys define the basis for establishing relationships with other tables. | Foreign keys establish relationships and connect data between related tables. |
This table summarizes the major difference between primary and foreign keys, highlighting their definitions, basic functionalities, NULL values treatment, duplicates handling, indexing, impact on deletion and insertion operations, applicability to temporary tables, and their roles in establishing relationships between tables.
Here are some additional differences between primary key and foreign key, presented in bullet point form:
Here are some differences between primary key and foreign key in terms of uses:
In this guide we have understood the major differences and similarities between primary vs foreign keys. The primary and foreign keys are important concepts and tools used in relational database management systems (RDBMS). The primary key identifies each record in a table, while the foreign key is used to establish relationships between tables. Both keys are essential components of any database, as they provide structure and integrity to the stored data.
Learning the differences between these two types of keys can help you more effectively manage your databases and ensure that your data remains accurate and secure.
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