SQL Query and performance tuning - Joins in depth
🔗 Joins vs. Subqueries: What to Use and How It Works Behind the Scenes When you're working with SQL, you'll often face this question: Should I use a JOIN or a SUBQUERY? Both get the job done. But behind the scenes, your choice can affect performance, sometimes dramatically. Let’s break down the difference , peek under the hood at how joins actually work, and help you choose the right one. 🧩 What’s the Difference? Let’s say you have two tables: customers (id, name, region_id) regions (id, region_name) 🔁 Option 1: Using a JOIN SELECT customers.name, regions.region_name FROM customers JOIN regions ON customers.region_id = regions.id; 🧠 Option 2: Using a SUBQUERY SELECT name, ( SELECT region_name FROM regions WHERE regions.id = customers.region_id) AS region_name FROM customers; ✅ Both queries return the same result. But what happens under the hood? 🛠️ How Joins Actually Work Let’s break down three core join algorithms used by SQL engi...