Explain the purpose and structure of Common Table Expressions (CTEs) in SQL, and discuss scenarios where CTEs are preferred over subqueries for improving query readability and maintainability.

Define CTEs as reusable query components that enhance readability. Explain their structure using the WITH clause and recursive capabilities. Highlight scenarios where CTEs improve clarity over subqueries, such as complex joins or hierarchical data. Emphasize maintainability through modular code and reuse. Contrast with subqueries by noting CTEs' ability to reference themselves or other CTEs, aiding in debugging and logical separation.

Common Table Expressions (CTEs) are named temporary result sets defined within the WITH clause, enabling modular query construction. They improve readability by breaking down complex queries into logical segments, such as calculating sales metrics across multiple tables. CTEs are preferred over subqueries in scenarios involving recursive data (e.g., organizational hierarchies) or repeated calculations, as they avoid redundancy and enhance maintainability. For example, a CTE can compute intermediate metrics once and be reused across multiple parts of a query. Unlike subqueries, CTEs support recursion and can be referenced multiple times, simplifying nested logic. However, they may introduce slight performance overhead in some cases, requiring optimization for large datasets. Overall, CTEs balance clarity and functionality, making them ideal for complex analytical tasks.