text: -- Select within Select tutorial
  
  -- 1 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')
  
  -- 2 Show the names of 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');
  
  -- 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 = (SELECT continent FROM world WHERE name = 'Argentina') 
  OR continent = (SELECT continent FROM world WHERE name = '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 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(100*population/(SELECT population 
  FROM world WHERE name = 'Germany')), '%') 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 x
      WHERE area >= ALL
  (SELECT area FROM world y
      WHERE y.continent=x.continent
          AND population>0)
  
  -- 8 List each continent and the name of the country that comes first alphabetically.
  SELECT continent, name FROM world x 
    WHERE name <= ALL (SELECT name FROM world y 
      WHERE y.continent = x.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 
    WHERE continent IN (SELECT continent FROM world  x 
      WHERE 25000000 >= (SELECT MAX(population) FROM world y 
        WHERE x.continent = y.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 x 
    WHERE population > ALL (SELECT population*3 FROM world y 
      WHERE y.continent = x.continent AND y.name != x.name);