Mastering Joins and Window Functions in SQL

Introduction. If you’re working with data — especially in tools like Power BI, Excel, or databases like MySQL or PostgreSQL — understanding Joins and Window Functions is a game changer. These two concepts help you combine data and analyze it in powerful ways without losing detail. Here is an article to guide you through joins and window functions. 🔗 What Are Joins? A Join combines rows from two or more tables based on a related column. Importance of joins. Most databases are structured into multiple tables to avoid duplication. To analyze the data meaningfully, you need to bring those tables together. Types of Joins 1️⃣ INNER JOIN Returns only the matching records in both tables. Example; SELECT customers . name , orders . order_date FROM customers INNER JOIN orders ON customers . customer_id = orders . customer_id ; ` Meaning: Only customers who have placed orders will appear. 2️⃣ LEFT JOIN (LEFT OUTER JOIN) Returns all records from the left table and matching records from the right t