- Show the total population of the world.
SELECT SUM(population)
FROM world
- List all the continents - just once each.
select distinct continent
from world
- Give the total GDP of Africa
select sum(gdp)
from world
where continent = 'Africa'
- How many countries have an area of at least 1000000
select count(name)
from world
where area >= 1000000
- What is the total population of (‘Estonia’, ‘Latvia’, ‘Lithuania’)
select sum(population)
from world
where name in ('Estonia', 'Latvia', 'Lithuania')
- For each continent show the continent and number of countries.
select continent, count(name)
from world
group by continent
having count(name)
- For each continent show the continent and number of countries with populations of at least 10 million.
select continent, count(name)
from world
where population >= 10000000
group by continent
- List the continents that have a total population of at least 100 million.
select continent
from world
group by continent
having sum(population) >= 100000000
本文介绍了使用SQL进行数据查询的基本技巧，包括计算世界总人口、列出各洲名称、计算非洲GDP总额、筛选面积超过一百万平方公里的国家数量、统计特定国家群体的人口总数、按洲分组统计国家数目、找出人口至少一千万的国家数量以及确定总人口不少于一亿的洲份。
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