What is the purpose of common table expressions in SQL and when should you use them?
Common table expressions are temporary result sets that can be utilized in SELECT, INSERT, UPDATE, or DELETE statements. They simplify complex queries and improve readability by breaking down the query into smaller, more manageable pieces. They also have the potential to improve performance in large, complex queries and are particularly useful when working with hierarchical or recursive data. In summary, common table expressions are a valuable tool for optimizing SQL queries and making them more readable and maintainable.
Could you include small examples?