Subqueries
Nested Subqueries: Multi-Level Logic
Senior Data Analyst
February 23, 2026
5 min read
The Three-Level Filter
I needed: "Orders from customers who are in regions that had a promo last month." This required nesting.
The Implementation
SELECT * FROM orders
WHERE customer_id IN (
SELECT id FROM customers
WHERE region_id IN (
SELECT region_id FROM promotions
WHERE promo_month = '2026-01'
)
);
Pro Tip
If you nest more than 2 levels, strongly consider using CTEs for readability. Code that's hard to read is hard to debug.
*Day 55: CTEs vs. Subqueries—A Comparison.*