SQL Subqueries & CTE | Correlated, Recursive CTE + Interview Questions

This is where SQL starts to feel advanced, and also where it gets really interesting. In this video we’ll learn how to write a query inside another query, and then how to make those long, complicated queries clean and readable using CTEs. I’ll also solve the same problem in 4 different ways, so you can see there’s never just one right answer in SQL. Here’s what we cover: ✅ Subqueries in WHERE, FROM, SELECT and HAVING ✅ Scalar, multi-row and correlated subqueries ✅ EXISTS and NOT EXISTS ✅ One problem, 4 solutions: NOT IN, LEFT JOIN, EXCEPT and NOT EXISTS ✅ CTEs using the WITH clause, and chaining multiple CTEs ✅ Recursive CTEs: employee hierarchy, management chain and Fibonacci Then we solve 5 interview questions: Immediate Food Delivery II, Monthly Transactions II, Restaurant Growth, Game Play Analysis (day-1 retention) and a FIFA World Cup case study. Some of these are marked hard on LeetCode, but don’t worry, I break each one down step by step. If correlated subqueries feel confusing the first time, that’s completely normal. Watch that part twice and it will click. ⏱️ Chapters 0:00 SQL Subqueries: Single Row, Multi Row, Correlated & Nested 1:58:59 CTE: WITH Clause & Recursive CTE 3:18:34 Interview Q: Percentage of Immediate Orders 3:30:13 Interview Q: Monthly Transactions & Chargebacks 3:47:31 Interview Q: Restaurant Growth 4:08:35 Interview Q: Day-1 Retention (Game Play Analysis) 4:32:56 Case Study: FIFA World Cup Match Analysis If you want to become a Data Engineer, check out my Ultimate Data Engineering Program here: https://trendytech.in If you want to become an AI Engineer, check out my Agentic AI Engineering Program here: https://trendytech.in/agentic-ai/ 🔗 Let’s connect! LinkedIn:   / bigdatabysumit   Twitter:   / bigdatasumit   Instagram:   / data.engineering.by.sumit