-- A Microsoft Azure Supercloud customer is defined as a company that purchases at least one product from each product category. -- Write a query that effectively identifies the company ID of such Supercloud customers. -- Solution : WITH supercloud_customers AS ( SELECT customer_id FROM ( SELECT customer_id, COUNT(DISTINCT product_category) AS category_count FROM customer_contracts cc JOIN products p USING (product_id) GROUP BY 1 ) x WHERE category_count = (SELECT COUNT(DISTINCT product_category) FROM products) ) SELECT customer_id FROM supercloud_customers -- my approach: wasn't sure on how to add "category_count". WITH supercloud_customers as ( SELECT customer_id, product_category, count(product_id) FROM customer_contracts cc JOIN products p USING(product_id) GROUP BY 1, 2 ORDER BY 1, 2 ) SELECT customer_id FROM supercloud_customers -- remarks: