CREATE TABLE products (product_id VARCHAR2, product_price VARCHAR2)
CREATE TABLE staff (last_name VARCHAR2, staff_id VARCHAR2)
CREATE TABLE complaints (staff_id VARCHAR2, product_id VARCHAR2)

Find the last name of the staff member who processed the complaint of the cheapest product.
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
SELECT "t1"."last_name" FROM "staff" "t1" JOIN "complaints" "t2" ON "t1"."staff_id" = "t2"."staff_id" JOIN "products" "t3" ON "t2"."product_id" = "t3"."product_id" ORDER BY "t3"."product_price" FETCH FIRST 1 ROWS ONLY