Table schema:
CREATE TABLE products (product_id VARCHAR, product_price VARCHAR); CREATE TABLE complaints (staff_id VARCHAR, product_id VARCHAR); CREATE TABLE staff (last_name VARCHAR, staff_id VARCHAR)

Question: Find the last name of the staff member who processed the complaint of the cheapest product.
SQL: SELECT t1.last_name FROM staff AS t1 JOIN complaints AS t2 ON t1.staff_id = t2.staff_id JOIN products AS t3 ON t2.product_id = t3.product_id ORDER BY t3.product_price LIMIT 1