SQLZOO——SELECT within SELECT Tutorial

Bigger than Russia

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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

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2.

Show the countries in Europe with a per capita GDP greater than 'United Kingdom'.

Per Capita GDP

The per capita GDP is the gdp/population

select name
from world
where continent = 'Europe' and gdp/population >
     ( select gdp/population
       from world
       where name = 'United Kingdom')

Neighbours of Argentina and Australia

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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 Canada and Poland

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4.

Which country has a population that is more than United Kingom 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

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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:

select name,concat(cast(round(100*population/(select population from world where name='Germany'),0) as int),'%')
from world
where continent='Europe'

 注意：

cast 函数：类型转换；concat 函数：字符串拼接；round函数：四舍五入

Bigger than every country in Europe

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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 is not null and continent = 'Europe')

Largest in each continent

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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)

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8.

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

select continent, name
from world a where name <= all
(select name from world b where a.continent = b.continent)

Difficult Questions That Utilize Techniques Not Covered In Prior Sections

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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 a
where 25000000 >= all
  (select population
   from world b
   where a.continent = b.continent)

Three time bigger

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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 a
where a.population/3 >= all
  (select population
   from world b
   where a.continent = b.continent and a.name != b.name)