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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')

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 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 ('South America','Oceania')
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.

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 %

You can use the function CONCAT to add the percentage 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 the continent, the name and the area:

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

8.

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

#法一：
SELECT continent,name
FROM world AS x
WHERE x.name=(SELECT y.name
               FROM world AS y
               WHERE y.continent=x.continent
               ORDER BY name 
               LIMIT 1)
#法二；
SELECT continent, MIN(name) AS name
FROM world 
GROUP BY continent
ORDER BY continent 

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 AS x
WHERE 25000000 > ALL(SELECT population
                     FROM world AS 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 AS x
WHERE population/3 > ALL(SELECT population
                         FROM world AS y
                         WHERE x.continent=y.continent
                         AND x.name <> y.name
                         AND population > 0)