Optimization: EXISTS vs IN Large Subquery

Interviewer prompt: Pick better query for finding customers with paid orders on very large tables. Query A: SELECT c.customer_id FROM customers c WHERE c.customer_id IN (SELECT o.customer_id FROM orders o WHERE o.status = 'PAID'); Query B: SELECT c.customer_id FROM customers c WHERE EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.customer_id AND o.status = 'PAID');