SQL Challenge: Can You Spot the Hidden Data Leak? 🔍 Below is a common SQL query designed to calculate Average Order Value (AOV) per customer over the last quarter. At first glance, it runs smoothly and returns a result. But there is a subtle, critical logic flaw hiding in plain sight that distorts the business metrics. SELECT c.customer_id, c.customer_name, AVG(o.order_amount) AS avg_order_value, COUNT(o.order_id) AS total_orders FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id WHERE o.order_date >= '2026-05-01' GROUP BY c.customer_id, c.customer_name; 🛠️ The Challenge Can you identify why this query produces inaccurate business reporting? 💡 Hint & Solution Breakdown The Hidden Flaw: Using WHERE o.order_date >= ... on a LEFT JOIN table implicitly converts your query into an INNER JOIN! Why it breaks: Any customer who made 0 orders in that timeframe will have a NULL order_date. The WHERE clause filters out those NULL rows entirely instead of keeping the customer in the result set with 0 orders. The Impact: Your report will completely exclude inactive customers, artificially inflating your overall engagement metrics! ✅ The Fixed Query To preserve your LEFT JOIN and retain all customers (even those with zero orders), move the date filter directly into the ON clause: SELECT c.customer_id, c.customer_name, COALESCE(AVG(o.order_amount), 0) AS avg_order_value, COUNT(o.order_id) AS total_orders FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id AND o.order_date >= '2026-05-01' GROUP BY c.customer_id, c.customer_name; Key Takeaways Watch Where You Filter: Filtering a LEFT JOIN table in the WHERE clause converts it to an INNER JOIN. Preserve Inactive Records: Move conditional logic for joined tables into the ON clause to keep zero-count or inactive entities. Wrap Nulls Safely: Always use COALESCE() on aggregated fields to avoid returning empty NULL values to business dashboards. CTA Ready to sharpen your SQL logic, master data modeling, and solve complex real-world analytics problems? Join the Techawks Data Science & Analytics Program today to build production-grade projects and elevate your data career! 🚀