We’ve all seen it. The massive, deeply nested SQL query with subqueries inside subqueries. It’s impossible to read, a nightmare to debug, and usually performs terribly. Early in my career as a BI Engineer, I wrote queries like that. Then, I learned about CTEs (Common Table Expressions) . Using the WITH clause changed how I write SQL forever. But simply replacing a subquery with a CTE is just the beginning. Here are 3 advanced CTE patterns I use in production to handle millions of records cleanly and efficiently. 1. The "Pipeline" Pattern (Breaking Down Complex Logic) The most common mistake is trying to do all aggregations, joins, and filtering in one giant SELECT statement. Instead, use CTEs to create a logical "pipeline" where each step does exactly one thing. This makes debugging incredibly easy because you can SELECT * from any intermediate step to see what the data looks like.…