What are the ids of all suppliers?
select supplier_id from product_suppliers
What is the average of total amount purchased?
select avg(total_amount_purchased) from product_suppliers
Find the id of suppliers whose average amount purchased for each product is above 50000 or below 30000.
select supplier_id from product_suppliers group by supplier_id having avg(total_amount_purchased) > 50000 or avg(total_amount_purchased) < 30000