Structure. Primary Key and Foreign Key

Primary and Foreign Keys

In relational databases, the foundation lies in tables and their relationships, which are often established using Primary Keys and Foreign Keys.

A Primary Key (PK) serves as a unique identifier for a record within a table;
A Foreign Key (FK) references the Primary Key of a different table, connecting records between them.

Take, for instance, two tables: "student" and "group." In the "student" table, each record might have details such as id (representing the student's ID), name, surname, age, and group_id (which is a foreign key pointing to the primary key of the "group" table). The "group" table, on the other hand, might contain id (indicating the group's ID), name, and grade.

From this, it's evident that both John and Kesha are members of the BG1 group, as indicated by their foreign key referencing the group id. The BG4 group has one student, Emma, while the MG2 group currently has no students associated with it.

Such a structure facilitates the use of JOIN operations in database queries.

Take a closer look at the "group-student" entity-relationship (ER) diagram:

1. What is a primary key?

2. What is a foreign key?

Everything was clear?

Thanks for your feedback!

Section 2. Chapter 1

Ask AI

Ask anything or try one of the suggested questions to begin our chat

Course Content

Relational Database and Normalization

1. Database Models

Introduction Difference between Relational and Non-relational Databases Entity-Relationship Model Entity-Relationship Model. Relationships

2. Relational Database

Structure. Primary Key and Foreign Key Foreign Key Constraints. ON DELETE Options Many-to-One and One-to-Many One-to-One and Many-to-Many

3. Normalization and Normal Forms

Normalization First Normal Form Second Normal Form Third Normal Form