sqlzoo练习答案--SELECT within SELECT Tutorial

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本文介绍如何使用SQL子查询完成复杂的数据检索任务，包括基于人口、GDP等条件筛选国家信息的具体案例。

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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)

[sql]view plaincopy 
    
 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'.

[sql]view plaincopy 
    
 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.

[sql]view plaincopy 
    
 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.

[sql]view plaincopy 
    
 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 %

[sql]view plaincopy 
     
 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)

[sql]view plaincopy 
     
 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 :

[sql]view plaincopy 
     
 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.

[sql]view plaincopy 
     
  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.

[sql]view plaincopy 
     
 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.

[sql]view plaincopy 
     
 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)  