SELECT within SELECT Tutorial.sql

#List each country name where the population is larger than that of 'Russia'.
SELECT name
FROM world
WHERE population >
	(SELECT population
		FROM world
		WHERE name = 'Russia');

#Show the countries in Europe with a per capita GDP greater than 'United Kingdom'.
SELECT name
FROM world
WHERE continent = 'Europe' AND gdp/population >
	(SELECT gdp/population
		FROM world
		WHERE name = 'United Kingdom');
        
#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;

#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');

#Show the name and the population of each country in Europe. Show the population as a percentage of the population of Germany.
SELECT name, CONCAT(ROUND((population/(SELECT population FROM world WHERE name = 'Germany'))*100,0),'%')
FROM world 
WHERE continent = 'Europe';

#find the largest country in the world
SELECT name
FROM world
WHERE population >= ALL(
	SELECT population 
		FROM world
		WHERE population>0);

#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 > (SELECT MAX(gdp) FROM world WHERE gdp IS NOT NULL AND continent = 'Europe');

#Find the largest country (by area) in each continent, show the continent, the name and the area:
SELECT continent, name, area
FROM world w1
WHERE (continent, area) IN 
	(SELECT continent, MAX(area) FROM world w2
		WHERE w1.continent = w2.continent
		GROUP BY continent);

#List each continent and the name of the country that comes first alphabetically.
SELECT continent, name
FROM world w1
WHERE name = (
SELECT name FROM world w2 WHERE w1.continent = w2.continent ORDER BY name ASC 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 w1
WHERE 25000000 >= ALL (SELECT population FROM world w2 
                              WHERE w1.continent = w2.continent
                              AND population > 0);
                              
#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 w1
WHERE population >= ALL (SELECT 3*population FROM world w2
                           WHERE w1.continent = w2.continent 
                           AND w1.name <> w2.name);