```select v.vend_id, count(prod_id)
from Products p right join Vendors v 
on p.vend_id = v.vend_id 
group by vend_id
order by vend_id

v.vend_id代表所有供应商都要列出来，right join 连接vendors 表示 要count所有存在的prod_id，如果有v.vend_id在vendors表中没出现，那么count（prod_id）计算null则返回0