-- 1. Maak een lijst van klanten zonder bestellingen in de afgelopen maand. -- Structuur: -- customers (customer_id, name, registration_date) -- orders (order_id, customer_id, order_date, amount) SELECT DISTINCT c.customer_id, c.name FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id and o.order_date >= DATE_TRUNC('month', CURRENT_DATE) - INTERVAL '1 month') WHERE o.amount IS NULL -- 2. Bereken het aandeel van elke subcategorie in de totale omzet van de categorie -- sales (product_id, category, subcategory, revenue, sale_date) -- Verwachte resultaat: category | subcategory | share_of_category