untitled.md

SELECT within 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.

name	continent	area	population	gdp
Afghanistan	Asia	652230	25500100	20343000000
Albania	Europe	28748	2831741	12960000000
Algeria	Africa	2381741	37100000	188681000000
Andorra	Europe	468	78115	3712000000
Angola	Africa	1246700	20609294	100990000000
...

You might want to look at these examples first

Using SUM, Count, MAX, DISTINCT and ORDER BY.

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 ('Estonia', 'Latvia', 'Lithuania')

SELECT SUM(population)
FROM world
WHERE name in  ('Estonia', 'Latvia', 'Lithuania');

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