SQL Subqueries vs CTEs: Choosing the Right Tool
Subqueries and CTEs solve similar problems. After using both for years, here is how I choose between them for each situation. Subqueries and CTEs are two ways to break a complex query into steps. Both let you compute an intermediate result and use it in a larger query. Developers often ask me which to use, and the honest answer is: it depends on the query, the team, and the database. After writing thousands of both, I have developed clear rules for when each is the better choice. The Fundamental Difference A subquery is a query nested inside another query. It is defined inline, at the point where it is used. A CTE is defined at the top of the query with a name, then referenced by that name in the body. The structural difference is about where the intermediate result is defined and how visible it is to a reader. . Subquery: defined inline SELECT customer_id, order_count FROM ( SELECT customer_id, COUNT(*) AS order_count FROM orders GROUP BY customer_id ) sub WHERE order_count > 5; . CTE: defined at the top, referenced by name WITH order_counts AS ( SELECT customer_id, COUNT(*)…