Find the emails of customers who has filed a complaints of the product with the most complaints.
CREATE TABLE customers (email_address VARCHAR, customer_id VARCHAR); CREATE TABLE complaints (customer_id VARCHAR)
[SQL] SELECT t1.email_address FROM customers AS t1 JOIN complaints AS t2 ON t1.customer_id = t2.customer_id GROUP BY t1.customer_id ORDER BY COUNT(*) LIMIT 1 [/SQL]