SQLZOO:SELECT within SELECT Tutorial

1.List each country name where the population is larger than that of ‘Russia’.

world(name, continent, area, population, gdp)

SELECT name 
FROM world
WHERE population > (SELECT population 
      FROM world
      WHERE name='Russia')

2.Show the countries in Europe with a per capita GDP greater than ‘United Kingdom’.

Per Capita GDP
The per capita GDP is the gdp/population

select name
from world
where (gdp/population) > (select gdp/population 
						from world 
						where name='United Kingdom')
and continent='Europe';

3.List the name and continent of countries in the continents containing either Argentina or Australia. Order by name of the country.

select name,continent
from world
where continent in (select continent 
					from world 
					where name in ('Argentina','Australia'))
order by name;

4.Which country has a population that is more than Canada but less than Poland? Show the name and the population.

select name,population
from world
where population > (select population 
					from world 
					where name='Canada') 
and population < (select population 
				  from world 
				  where name='Poland');

5.Germany (population 80 million) has the largest population of the countries in Europe. Austria (population 8.5 million) has 11% of the population of Germany.

Show the name and the population of each country in Europe. Show the population as a percentage of the population of Germany.

The format should be Name, Percentage for example:

name	percentage
Albania	3%
Andorra	0%
Austria	11%
…	…

Decimal places
You can use the function ROUND to remove the decimal places.
Percent symbol %
You can use the function CONCAT to add the percentage symbol.

select name,concat(round(population/
					(select population 
				   	from world 
					where name='Germany')*100,0),'%')
from world
where continent='Europe';

6.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);

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

SELECT continent, name, area 
FROM world as x
WHERE area >= ALL(SELECT area
				  FROM world y
				  WHERE y.continent=x.continent
				  order by continent
				  AND area>0);

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

select continent,name
from (select continent,name, row_number() over(partition by continent 
											   order by name)as a
	  from world
	  order by continent) as newtable
where newtable.a=1;

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

select continent, name 
from world a 
where name <= all(select name 
				  from world b 
				  where a.continent=b.continent)

9.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);

10.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 
						   	  and b.population>0);