SQLZOO——5 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.

Total world population

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1.

Show the total population of the world.

world(name, continent, area, population, gdp)

SELECT SUM(population)
FROM world

 

List of continents

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2.

List all the continents - just once each.

select distinct continent
from world

 

GDP of Africa

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3.

Give the total GDP of Africa

select sum(gdp)
from world
where continent = 'Africa'

Count the big countries

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4.

How many countries have an area of at least 1000000

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

  

Baltic states population

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5.

What is the total population of ('Estonia', 'Latvia', 'Lithuania')

select sum(population)
from world
where name in ('Estonia', 'Latvia', 'Lithuania')

Counting the countries of each continent

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6.

For each continent show the continent and number of countries.

select continent,count(name)
from world
group by continent

Counting big countries in each continent

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 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