Mastering SQL Joins and Window Functions: A Practical Guide with an E‑commerce Dataset

Introduction & The Dataset If you're working with SQL, you've probably used basic SELECT statements, filtered with WHERE , and maybe even done some simple aggregations. But the real power of SQL unfolds when you start combining data from multiple tables and performing complex calculations across rows without losing detail. That's where JOINs and Window Functions come in. In this article, we'll dive deep into these advanced concepts using a realistic e‑commerce dataset. By the end, you'll be able to: Combine data from multiple tables using different types of joins. Perform rankings, running totals, and comparisons across rows with window functions. Organize complex queries using Common Table Expressions (CTEs). Solve practical business questions that real data analysts face every day. We'll use a consistent dataset throughout – so you can follow along, try the queries yourself, and truly master these techniques. Meet Our Data Imagine we're running an online store. Our database has three