10-4 4-4 查询具有最高价格的机器的型号，机器包括PC、Laptop、Printer (10 分)

SELECT a.model
from (
	SELECT price,model
	from pc
	UNION
	SELECT price,model
	from laptop
	UNION
	SELECT price,model
	from printer
)as a
WHERE a.price =(
	SELECT max(b.price)
	FROM (
		SELECT price,model
		from pc
		UNION
		SELECT price,model
		from laptop
		UNION
		SELECT price,model
		from printer
	)b
)	

10-7 5-1 查询销售便携式电脑但不销售PC的厂商 (10 分)

SELECT maker
FROM product p,laptop l
WHERE p.model=l.model and maker not in(
SELECT maker
    FROM product p,pc 
    WHERE p.model=pc.model
)

10-8 5-2 查询至少生产两种不同的计算机(PC或便携式电脑)且机器速度至少为133的厂商

select maker
from (
    select maker,model
    from product
    where model in (
        select model
        from pc
        where speed>=133
    )
    union
    select maker,model
    from product
    where model in (
        select model
        from laptop
        where speed>=133
    )
) as a
group by maker
having count(maker)>=2

10-9 5-3 查询生产最高速度的计算机(PC或便携式电脑)厂商 (10 分)

select maker
from (
    select model, maker
    from product
    where speed in (
        select MAX(speed)
        from 
    )
    union
    select model, maker
    from product
    where speed in (
        select MAX(speed)
        from laptop
				union
        select MAX(speed)
        from pc
    )
) as a
ORDER BY maker