Lecture 1: Join Overview

🎯 Learning Objectives

By the end of this lecture, you will be able to:

• Define the JOIN operator.
• Explain the role of primary keys and foreign keys in a JOIN operation.
• Identify the different types of JOIN operators in SQL.

🧠 Concept Overview

A simple SELECT statement retrieves data from one or more columns of a single table.

However, in real-world databases, data is often spread across multiple related tables.

To retrieve connected information from these tables, we use the JOIN operator.

🔗 What is a JOIN?

• A JOIN combines rows from two or more tables based on a relationship between specific columns in those tables.
• These relationships are usually established through primary keys and foreign keys.

📘 Example (Library Database Model)

In a simplified library system:

• Entities include Author, Book, Borrower, Loan, and Copy.
• Each entity is represented by a separate table.