How many customers bought each product?
select count (distinct t1.customer_id) from customer_orders as t1 join order_items as t2 on t1.order_id = t2.order_id join products as t3 on t2.product_id = t3.product_id group by t3.product_id
Which products were bought by at least two distinct customers?
select * from customer_orders as t1 join order_items as t2 on t1.order_id = t2.order_id join products as t3 on t2.product_id = t3.product_id group by t3.product_id having count (distinct t1.customer_id) >= 2
What are the product names?
select distinct t3.product_name from customer_orders as t1 join order_items as t2 on t1.order_id = t2.order_id join products as t3 on t2.product_id = t3.product_id group by t3.product_id having count (distinct t1.customer_id) >= 2