SqlZoo.net习题答案：Using SUM, COUNT, MAX, AVG, DISTINCT and ORDER BY.

习题地址：http://sqlzoo.net/2.htm

 

表结构：bbc(name, region, area, population, gdp)

 

1b.List all the regions - just once each.

select distinct region 
from bbc

 

1c.Give the total GDP of Africa

select sum(GDP) 
from bbc 
where region = 'Africa'

 

1d.How many countries have an area of at least 1000000

select count(name) 
from bbc 
where area >= 1000000

 

1e.What is the total population of ('France','Germany','Spain')

select sum(population) from bbc 
where name in ('France','Germany','Spain')

 

2a.For each region show the region and number of countries.

select region, count(name) 
from bbc 
group by region

 

2b.For each region show the region and number of countries with populations of at least 10 million.

select distinct region, count(name)
from bbc
where population >= 10000000 
group by region

 

2c.List the regions with total populations of at least 100 million.

select region 
from bbc 
group by region 
having sum(population) >= 100000000