Why Your SQL JOIN Creates Duplicate Rows (Finally Explained Visually)

Have you ever written a SQL JOIN… and suddenly your rows multiplied unexpectedly? In this video, I explain visually WHY SQL JOINs create duplicate rows and how real engineers actually debug and fix this problem. Timestamp: 00:00 Why SQL JOINs create duplicate rows 00:22 Creating the problem with customers and orders tables 00:49 Understanding one-to-many relationships 01:02 Why John appears multiple times 01:13 Visual explanation of JOIN matching 01:43 What is one-to-many mapping? 02:19 Joining multiple tables 03:26 How real engineers fix duplication 03:34 Summarizing data before JOIN 03:49 Using GROUP BY to control duplicates 03:59 Using CTE for cleaner SQL 04:07 Final CTE solution explained 04:56 Real production dangers of bad JOINs 05:05 Why JOIN problems are relationship problems I’ll explain everything step-by-step using simple examples and visual diagrams so the concept becomes easy permanently. 📌 Topics Covered: - SQL JOIN - Duplicate Rows in SQL - One-to-Many Mapping - SQL CTE - GROUP BY - SQL for Beginners - SQL Interview Questions - Data Engineering SQL Concepts If this video helped you understand SQL better, consider subscribing to support the channel ❤️ #SQL #DataEngineering #LearnSQL#SQLTutorial#DataAnalyst