SQLZOO Select within Select Practice Solutions.

Bigger than Russia

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');
									  
								
							

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 as per_capita_gpd
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;
								
							

Between United Kingdom and Germany

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');
								
							

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.

								
SELECT name, CONCAT(ROUND((population* 100)/
(SELECT population FROM world
WHERE name = 'Germany'), 0),'%')
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 > 
(
    select max(gdp) from world
    where 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 x.continent, x.name, x.area
FROM world AS x
WHERE x.area = (
  SELECT MAX(y.area)
  FROM world AS y
  WHERE x.continent = y.continent)
								
							

First country of each continent (alphabetically)

8.

List each continent and 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
);
								
							

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
WHERE continent IN 
(
SELECT continent
FROM world  x
WHERE 25000000 >= 
    (SELECT MAX(population) FROM world y 
     WHERE x.continent = y.continent)
);
								
							

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 3*population
FROM world y
WHERE x.continent = y.continent AND x.name <> y.name
);