text: -- SELECT within SELECT
  
  -- 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='Romania')
  
  --  Answer 
  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'.
  
  --  Answer  
  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.
  
  --  Answer  
  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.
  
  -- Answer  
  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.
  
  
  --  Answer  
  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)
  
  --  Answer  
  SELECT name FROM world
    WHERE gdp > (SELECT MAX(gdp) FROM world WHERE continent='Europe')
  
  
  
  -- 7)
  -- Find the largest country (by area) in each continent, show the continent, the name and the area:
  SELECT continent, name, population FROM world x
    WHERE population >= ALL
      (SELECT population FROM world y
          WHERE y.continent=x.continent
            AND population>0)
  
  --  Answer  
  SELECT continent,name, area FROM world x
    WHERE area >= ALL
      (SELECT area FROM world y
          WHERE y.continent=x.continent
            AND area >0)
  
  
  
  -- 8)
  -- List each continent and the name of the country that comes first alphabetically.
  
  --  Answer  
  SELECT continent, name FROM world x
    WHERE name <= ALL(SELECT name FROM world y
          WHERE y.continent=x.continent ORDER BY name)
  ORDER BY 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.
  
  --  Answer  
  SELECT name, continent, population FROM world x
    WHERE 25000000 >= ALL
      (SELECT population FROM world y
          WHERE y.continent=x.continent)
  
  
  
  
  -- 10)
  -- Show year, subject, and name of people who won a 'Medicine' prize in an early year (before 1910,
  -- not including 1910) together with winners of a 'Literature' prize in a later year 
  -- (after 2004, including 2004)
  
  --  Answer  
  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)
  
  