Select product.maker, pc.model, max(pc.price) as m_price
from product, pc
where product.model=pc.model
group by product.maker, pc.model

case when pc.price is not null then max(pc.price) end as m_price

with isayka as (
Select product.maker, pc.model, max(pc.price) as m_price
from product, pc
where product.model=pc.model
group by product.maker, pc.model
union
Select product.maker, laptop.model, max (laptop.price) as m_price
from product, laptop
where product.model=laptop.model
group by product.maker, laptop.model
union
Select product.maker, printer.model, max(printer.price) as m_price
from product, printer
where product.model=printer.model
group by product.maker, printer.model)
select maker, max(case when m_price is not null then m_price end) as m_price
from isayka
group by maker

case when not exists (select t2.price from t1 t2 where t2.price is null and t2.maker=t3.maker) then max(t3.price)

with isayka as (
select s.class, count(*) as sunks
from ships as s
join outcomes as o
on o.ship=s.name
where o.result='sunk'
group by s.class
union
select o.ship, count(*) as sunks
from outcomes as o
join classes as c
on o.ship=c.class
where o.result='sunk'
group by o.ship)

select c.class, count(sunks) as sunks
from isayka as i
right join classes as c
on i.class=c.class
group by c.class