SQL Subquery and CTEs( Common Table Expressions)

What is a subquery? Subquery is a query nested inside another query statement. It allows the query to be modular which would otherwise require multiple queries to achieve the same result. It runs first and the result is used as input by another query. When to use it? It is an essential tool when used in the following scenarios: Filtering row data using the results from another query Applying aggregation functions such as SUM or AVG dynamically Simplify queries by breaking them into smaller, read