Difference between revisions of "SUM and COUNT"

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<p>Using <code>GROUP BY</code> and <code>HAVING</code>
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<p>[[Using GROUP BY and HAVING.]]</p>
 
<div class='qu'>
 
<div class='qu'>
 
For each '''region''' show the '''region''' and number of countries.   
 
For each '''region''' show the '''region''' and number of countries.   

Revision as of 14:40, 10 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(region)
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')

Using GROUP BY and HAVING.

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
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