SQL Subqueries vs CTEs: When to Use Each and Why It Matters

SQL offers two primary tools for querying within a query: subqueries and Common Table Expressions (CTEs). A subquery is nested inside another query using parentheses and can appear in the SELECT, FROM, or WHERE clause to return a value, list, or table-like result. A CTE, defined using a WITH clause, acts as a named temporary result set that exists only for the duration of the query and is written above the main statement for clarity. While both tools often solve the same problem with similar performance in modern databases, CTEs are generally easier to read, can be referenced multiple times, and support recursion for hierarchical data. Subqueries are best suited for simple, one-off inline logic, whereas CTEs are preferred when a query involves multiple steps or requires reusability and readability.