SQL ZOO练习——SELECT within SELECT

最近在练习SQL上学习，把结果发上来存个档。

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 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. 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/
  (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)

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 x.area >= 
    ALL(SELECT area FROM world y
          WHERE x.continent = y.continent
            AND y.area > 0)
  

8. List each continent and the name of the country that comes first alphabetically.

SELECT continent,name FROM world x 
  WHERE x.name=(SELECT name FROM world y 
                  WHERE y.continent=x.continent ORDER BY name 
                    LIMIT 1)

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)

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/3 >= ALL(SELECT population FROM world y
                            WHERE x.continent = y.continent AND
                              x.name != y.name 
                                AND y.population > 0)