SQL JOIN Types Explained With Practical Database Examples

A tutorial published on DEV Community breaks down four core SQL JOIN types — INNER, LEFT, RIGHT, and SELF — using a fictional Kenyan shop database called Duka. The guide demonstrates how relational databases store data across separate tables and how JOINs link them via shared keys to answer real-world business questions. Practical queries show use cases such as identifying which customers placed orders, spotting unordered products, and listing customers who have never made a purchase. Each JOIN type is paired with sample input tables and expected output to illustrate exactly which rows are returned and when. The tutorial positions SQL JOINs as essential tools for tasks ranging from customer analysis to inventory management.