本文主要是介绍sqlzoo-SUM and COUNT参考答案，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
对应链接：https://sqlzoo.net/wiki/SUM_and_COUNT
1.Show the total population of the world.
(译：查询世界总人口数)
SELECT SUM(population)
FROM world
2.List all the continents - just once each.
（译：查询所有的大洲名称-只查询一次）
select distinct(continent) from world
3.Give the total GDP of Africa
（译：查询非洲总的GDP值）
select sum(gdp) from world where continent = 'africa'
4.How many countries have an area of at least 1000000
(译：面积大于100万平方公里的国家有多少个)
select count(name) from world where area >= 1000000
5.What is the total population of (‘Estonia’, ‘Latvia’, ‘Lithuania’)
（译：爱沙尼亚、拉托维亚和立陶宛的总人口是多少）
select sum(population) from world where name in ('Estonia','Latvia', 'Lithuania')
6.For each continent show the continent and number of countries.
（译：查询每个大洲的名称及该大洲所包含的国家数）
select continent, count(name) from world group by continent
7.For each continent show the continent and number of countries with populations of at least 10 million.
（译：查询所有大洲名称及该大洲下人口超过一千万的国家数）
select continent, count(name) from world
where population >= 10000000
group by continent
8.List the continents that have a total population of at least 100 million.
（译：查询总人口数至少为一亿的大洲名称）
select continent from world
group by continent
having sum(population) >= 100000000
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