EXISTS in SQL Server: “has at least one”

EXISTS asks whether a subquery finds a row. It does not care how many. That is the right shape for “customers who have ever cancelled.”

Has a cancelled order

SELECT c.customer_id, c.first_name, c.last_name
FROM Customers c
WHERE EXISTS (
  SELECT 1 FROM Orders o
  WHERE o.customer_id = c.customer_id
    AND o.status = 'Cancelled'
);

SELECT 1 is a habit. EXISTS only checks for a row, not the value. A JOIN to cancelled orders can duplicate the customer if they cancelled twice.