SELECT within SELECT Tutorial
注意：where语句中对表示条件的需要用单引号， 下面的译文使用的是有道翻译如有不正确，请直接投诉有道
01.List each country name where the population is larger than that of 'Russia'.
译文：列出每个国家的人口超过“俄罗斯”的名字。
select name from world where population>(select population from world where name='Russia' )
02.Show the countries in Europe with a per capita GDP greater than 'United Kingdom'.
译文：显示欧洲国家的人均GDP大于“英国”。
select name from world where continent='Europe' and (GDP/POPULATION)>(select gdp/population from world where name='United Kingdom')
03.List the name and continent of countries in the continents containing either Argentina or Australia. Order by name of the country.
译文：列出包括阿根廷或澳大利亚在内的各大洲的国家名称和大洲。按国家名称排序。
select name,continent from world where continent in (select continent from world where name in('Argentina', 'Australia')) order by name
04.Which country has a population that is more than Canada but less than Poland? Show the name and the population.
译文：哪个国家的人口比加拿大多但比波兰少?显示名字和人口。
select name，population from world where population>(select population from world where name='Canada ') and population<(select population from world where name='Poland')
05.Show the name and the population of each country in Europe. Show the population as a percentage of the population of Germany.
译文：显示欧洲每个国家的名称和人口。显示人口占德国人口的百分比。
# 这题写的有点问题 concat拼接的时候自己在%加上了好多零
SELECT name,concat(round(population/(select population from world where name='Germany'),2)* 100, '%')
FROM world
WHERE continent='Europe'
06.Which countries have a GDP greater than every country in Europe? [Give the name only.] (Some countries may have NULL gdp values)
译文：哪些国家的GDP比欧洲的每个国家都高?只告诉我名字。(有些国家可能有零gdp值)
select name from world where GDP > (select max(GDP) from world where continent='Europe')
07.Find the largest country (by area) in each continent, show the continent, the name and the area:
译文：在每个洲找出最大的国家(按面积)，显示洲，名称和地区:
select continent,name,area from world where area in(select max(area) from world group by continent)
08.List each continent and the name of the country that comes first alphabetically.
译文：按字母顺序列出每个洲和国家名称。
SELECT continent,name FROM world a WHERE name <= ALL(SELECT name from world b WHERE a.continent = b.continent )ORDER by name
09.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.
译文：找出所有国家的人口都小于2500亿的大陆。然后找出与这些大陆相关的国家的名字。显示姓名，大陆和人口。
SELECT name,continent,population FROM world x WHERE 25000000 >= ALL(SELECT population FROM world y WHERE y.continent = x.continent)
10.Some countries have populations more than three times that of any of their neighbours (in the same continent). Give the countries and continents.
译文：有些国家的人口是其邻国(在同一大陆)的三倍还多。给出国家和大陆。
SELECT name,continent FROM world x WHERE x.population/3 >= ALL(SELECT population FROM world y WHERE y.continent = x.continent AND y.name != x.name)
练习网址：https://sqlzoo.net/wiki/SELECT_within_SELECT_Tutorial
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