--select avg(speed)
--from pc

--select avg(screen)
--from laptop join product on laptop.model = product.model
--group by product.maker

--select avg(speed)
--from laptop
--where price > 1000

--select avg(price)
--from pc join product on pc.model =  product.model
--where product.maker = 'A'

--select avg(price)
--from (select price, model
--from pc

--union all

--select price, model
--from laptop) as m1 join product on m1.model = product.model
--where product.maker = 'B'

--select avg(price)
--from pc
--group by speed

select maker, count(pc.code)
from product join pc on product.model = pc.model
group by maker
having count(pc.code) > 2