How many products does each suppler supply?
select count(*) from product_suppliers group by supplier_id
Which suppler supplies the most products? Give me the supplier id.
select supplier_id from product_suppliers group by supplier_id order by count(*) desc limit 1
What are the average amount purchased and value purchased for this supplier.
select avg(total_amount_purchased), avg(total_value_purchased) from product_suppliers where supplier_id = (select supplier_id from product_suppliers group by supplier_id order by count(*) desc limit 1)