[MySQL]練習問題4

Which countries have a GDP greater than every country in Europe? [Give the name only.] (Some countries may have NULL gdp values)

select name from world
where gdp > all(select gdp from world where continent = 'Europe' and gdp > 0)

Find the largest country (by area) in each continent, show the continent, the name and the area

select continent,name,area from world x
where area >= all(select area from world y where x.continent=y.continent and area > 0)

List each continent and the name of the country that comes first alphabetically.

select continent,name from world x
where name=(select name from world y where x.continent=y.continent limit 1)

Find the continents where all countries have a population <= 25000000. Then find the names of the countries associated with these continents. Show name, continent and population.

select name,continent,population from world a where 25000000>= all
(select population from world b where a.continent=b.continent)

Some countries have populations more than three times that of any of their neighbours (in the same continent). Give the countries and continents.

select name,continent from world a 
where a.population/3>= all
(select population from world b where a.continent=b.continent
and a.name!=b.name)