Summary  
This chapter explains how primary keys uniquely identify records and foreign keys reference those keys to establish relationships between tables for use in join operations.  

General domain of usage  
Relational database design

## 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:

A focused introduction to relational databases for beginners. This course covers the essential concepts: how relational databases differ from non-relational ones, the entity-relationship model, types of relationships, primary and foreign keys, and the basics of normalization. Learners will gain a solid foundation in how data is organized and structured in relational database systems, preparing them for practical SQL and further database studies.

Structure. Primary Key and Foreign Key

Primary and Foreign Keys

1. What is a primary key?

2. What is a foreign key?