题目链接：https://sqlzoo.net/wiki/SELECT_within_SELECT_Tutorial
1
select name from world
where population > (select population from world where name='Russia')
2
select name from world
where gdp/population >
(select gdp/population from world where name='United Kingdom')
and continent = 'Europe'
3
select name,continent from world
where continent in
(select continent from world where name in ('Argentina','Australia'))
order by name
4
select name,population from world
where population >
(select population from world where name='Canada')
and
population < (select population from world where name='Poland')
5
select name,concat(round(population*100/(select population from world
where name='Germany' ) ,0),'%') from world
where continent='Europe'
讲解
6
select name from world
where gdp > (select max(gdp) from world
where continent='Europe')
7
select continent,name,area from world x
where area >= ALL
(select area from world y
where y.continent=x.continent
and area >0)
8
SELECT continent, MIN(name) AS name
FROM world
GROUP BY continent
ORDER by continent
9
select name,continent,population from world x
where 25000000>=all
(select population from world y
where y.continent=x.continent)
10
select name,continent from world x
where x.population/3 >= all
(select population from world y
where y.continent=x.continent
and y.name!=x.name)
