CREATE TABLE customers (customer_id VARCHAR2)
CREATE TABLE complaints (product_id VARCHAR2)
CREATE TABLE products (product_name VARCHAR2, product_id VARCHAR2)

Which products has been complained by the customer who has filed least amount of complaints?
SELECT DISTINCT t1.product_name FROM products AS t1 JOIN complaints AS t2 ON t1.product_id = t2.product_id JOIN customers AS t3 GROUP BY t3.customer_id ORDER BY COUNT(*) LIMIT 1
SELECT DISTINCT "t1"."product_name" FROM "products" "t1" CROSS JOIN "customers" "t3" JOIN "complaints" "t2" ON "t1"."product_id" = "t2"."product_id" GROUP BY "t3"."customer_id" ORDER BY COUNT(*) FETCH FIRST 1 ROWS ONLY