What is a CTE and how does it differ from a subquery?

A CTE (Common Table Expression) is a named temporary result set defined in a WITH clause before the main query. Subquery: anonymous, defined inline (in FROM, WHERE, SELECT). CTE: named, defined once at the top, reusable multiple times in the main query. Readability: CTEs break complex queries into named steps (like functions). A 10-level nested subquery is unreadable; 10 CTEs is manageable. Perfor