text: /*  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'.
  */
  
  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 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%
  ...	...
  */
  
  SELECT name,CONCAT(
    ROUND(
      population/(
        SELECT population 
        FROM world 
        WHERE name = 'Germany'
      )*100
    ),'%'
  ) 
  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 gdp > 0 AND continent = 'Europe'
  );
  
  
  
  
  
  
  /*  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 area>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 x.continent = y.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 x 
  WHERE population <= 25000000 AND continent NOT IN(
    SELECT continent 
    FROM world y 
    WHERE x.continent = y.continent AND population > 25000000  
    );
  
  
  
  
  
  
  /*  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 x.name != y.name
  )
  
  
  
  
  
  
  