select_within_select_tutorial.sql

-- Bigger than Russia
-- 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')


-- Richer than UK               
-- 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')


-- Neighbours of Argentina and Australia
-- 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 asc


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

SELECT name, population
FROM world 
WHERE population > (SELECT population 
                    FROM world 
                    WHERE name = 'United Kingdom')
AND population < (SELECT population 
                  FROM world 
                  WHERE name = 'Germany')
ORDER BY name ASC


-- Percentages of Germany
-- 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
Percent symbol % 

*/

SELECT name, CONCAT(ROUND(population / (SELECT population 
                                        FROM world
                                        WHERE name = 'Germany')*100,0),'%') AS percentage
FROM world WHERE continent = 'Europe'



-- Bigger than every country in 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')




-- Largest in each continent
-- 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)



-- First country of each continent (alphabetically)
-- 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)




-- Difficult Questions That Utilize Techniques Not Covered In Prior Sections
-- 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 25000000 >= ALL(SELECT population
                      FROM world y
                      WHERE x.continent = y.continent
                      AND y.population>0);



-- Three time bigger               
-- 10. Some countries have populations more than three times that of all 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 x.continent = y.continent
                         and y.name != x.name)