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Revision as of 01:30, 27 July 2012
BBC 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.
Exercises
Using SUM, Count, MAX, DISTINCT and ORDER BY.
Show the total population of the world.
bbc(name, region, area, population, gdp)
SELECT SUM(population) FROM bbc
SELECT SUM(population) FROM bbc
List all the regions - just once each.
SELECT DISTINCT(region) FROM bbc
Give the total GDP of Africa
SELECT SUM(gdp) FROM bbc WHERE region = 'Africa'
How many countries have an area of at least 1000000
SELECT COUNT(name) FROM bbc WHERE area >= 1000000
What is the total population of ('France','Germany','Spain')
SELECT SUM(population) FROM bbc WHERE name IN('France','Germany','Spain')
For each region show the region and number of countries.
SELECT region, COUNT(name) FROM bbc GROUP BY(region)
For each region show the region and number of countries with populations of at least 10 million.
SELECT region, COUNT(name) FROM bbc WHERE population >= 10000000 GROUP BY(region)
List the regions with total populations of at least 100 million.
SELECT region FROM bbc GROUP BY region HAVING SUM(population)>= 100000000
What next
The nobel table can be used to practice more SUM and COUNT functions.
