sqlzoo练习答案--SELECT within SELECT Tutorial

This tutorial looks at how we can use SELECT statements within SELECT statements to perform more complex queries.

name	continent	area	population	gdp
Afghanistan	Asia	652230	25500100	20343000000
Albania	Europe	28748	2831741	12960000000
Algeria	Africa	2381741	37100000	188681000000
Andorra	Europe	468	78115	3712000000
Angola	Africa	1246700	20609294	100990000000
...

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 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.

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') order by name

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.

Decimal places

Percent symbol %

select name,CONCAT(ROUND(100*population/(select population from world where name='Germany')),'%') 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 thecontinent, the name and the area:

SELECT continent, name, area FROM world x
  WHERE x.area >=
    ALL(SELECT y.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 x.name=(select y.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 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 x.population/3 >= all(select population from world y where x.continent=y.continent and x.name!=y.name and y.population>0)