sqlzoo练习--SELECT in SELECT

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 (gdp/population)> (SELECT gdp/population
                           FROM world
                          WHERE name='United Kingdom') 
 AND continent='Europe'

(千万不要忘记欧洲国家 )
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'
ORDER BY name

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 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.

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)

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 NOT IN (SELECT continent 
                          FROM world
                         WHERE population < 25000000)

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

总结：第八题和第十题稍微有点难度，里面涉及到关联子查询，需要强化该知识点 。