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)