sqlzoo练习答案--SUM and COUNT

World Country Profile: Aggregate functions

This tutorial is about aggregate functions such as COUNT, SUM and AVG. An aggregate function takes many values and delivers just one value. For example the function SUM would aggregate the values 2, 4 and 5 to deliver the single value 11.

namecontinentareapopulationgdpAfghanistanAsia6522302550010020343000000AlbaniaEurope28748283174112960000000AlgeriaAfrica238174137100000188681000000AndorraEurope468781153712000000AngolaAfrica124670020609294100990000000...

1、Show the total population of the world.

SELECT SUM(population)FROM world

2、List all the continents - just once each.

select DISTINCT(continent) from world

3、Give the total GDP of Africa

SELECT SUM(gdp)FROM world where continent='Africa'

4、How many countries have an area of at least 1000000

select count(name) from world where area>1000000

5、What is the total population of ('France','Germany','Spain')

SELECT SUM(population)FROM world where name in('France','Germany','Spain')

6、For each continent show the continent and number of countries.

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.

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.

select continent from world group by continent having sum(population)>=100000000