Master Oracle SQL Subqueries from absolute scratch!

In this complete masterclass, we break down everything you need to know about SQL subqueries—from basic rules and execution order to advanced concepts like correlated subqueries, inline views, and critical performance tuning. Whether you are preparing for a data interview or looking to write more efficient database queries, this guide has you covered. We use practical examples with standard EMP and DEPT tables, walk through common pitfalls (like how NULL breaks NOT IN), and wrap up with the top 10 interview questions you are guaranteed to face. 💡 Key Takeaways Covered in This Video: The Essentials: Understand how the inner query passes data to the outer query. Correlated vs. Non-Correlated: Why correlated subqueries execute for every single row and how it impacts performance. The NULL Pitfall: Why NOT IN returns zero rows if a NULL sneaks into your subquery, and how to fix it using NOT EXISTS. Performance Tuning: When to ditch a subquery in favor of a JOIN, and how indexes help.