EXISTS

How can we find customers who have at least one order?

Advanced⏱ 3 Minutes⭐ 1110 XP

🤔 THE QUESTION

How can we find customers who have at least one order?

💡 WHAT IS IT?

EXISTS tests for the existence of rows in a correlated subquery, returning true as soon as one match is found.

🎯 WHAT IS IT USED FOR?

High-performance presence checks, finding active purchasing customers, transactional auditing.

💻 EXAMPLE

SELECT c.customer_name
FROM customers c
WHERE EXISTS (
    SELECT 1
    FROM orders o
    WHERE o.customer_id = c.customer_id
);

Practice typing production-grade SQL code for EXISTS.