一：上码

--  查询生产最高速度的计算机(PC或便携式电脑)厂商，查询结果按照厂商升序排列

-- 分析：1.从pc表和product表当中当中找到速度最快的 表1
--       2.从laptop表和product表当中找到速度最快的 表2
--       3.将表1和表2联合起来找速度最快的


-- 1.
-- select maker,speed 
--       from pc,product
--       where pc.model = product.model
--       AND speed >= ALL(SELECT speed FROM pc);
      
-- -- 2.
-- select maker,speed
--         from laptop,product
--         where product.model = laptop.model
--         and speed >= all(select speed from laptop);
                
-- 3.
select maker 
    from (select maker,speed 
                  from pc,product
                  where pc.model = product.model
                  AND speed >= all(SELECT speed FROM pc)
         union
         select maker,speed
                  from laptop,product
                  where product.model = laptop.model
                  and speed >= all(select speed from laptop)) as temp1
    where temp1.speed >= all(select speed from (select maker,speed 
                                                      from pc,product
                                                      where pc.model = product.model
                                                      AND speed >= all(SELECT speed FROM pc)
                                                union
                                                 select maker,speed
                                                      from laptop,product
                                                      where product.model = laptop.model
                                                      and speed >= all(select speed from laptop))as temp2);