find the name of all products.
select name from products
which of them does Sony make.
select t1.name from products as t1 join manufacturers as t2 on t1.manufacturer = t2.code where t2.name = 'Sony'
Find the number of products that Sony does not make.
select count(distinct name) from products where name not in (select t1.name from products as t1 join manufacturers as t2 on t1.manufacturer = t2.code where t2.name = 'Sony')