SQL Subqueries and CTEs Explained With Real-World Data Analysis Examples

SQL subqueries and Common Table Expressions (CTEs) are techniques that help analysts break complex data questions into smaller, manageable steps. A subquery, also called a nested or inner query, is written inside another SQL query and passes its result to the outer query for further processing. For instance, finding employees who earn above the company average requires first calculating that average, which a subquery can handle automatically within a single statement. This approach is especially useful with dynamic data, as the query recalculates results each time it runs rather than relying on hardcoded values. The article further classifies subqueries by the number of values they return and how they interact with outer queries, alongside a comparison with CTEs.