SUM and COUNT
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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 |
| ... | ||||
Using SUM, Count, MAX, DISTINCT and ORDER BY.
Total world population
Show the total population of the world.
world(name, continent, area, population, gdp)
SELECT SUM(population)
FROM world
SELECT SUM(population)
FROM world
List of continents
List all the continents - just once each.
SELECT DISTINCT(continent)
FROM world
GDP of Africa
Give the total GDP of Africa
SELECT SUM(gdp)
FROM world
WHERE continent = 'Africa'
Count the big countries
How many countries have an area of at least 1000000
SELECT COUNT(name)
FROM world
WHERE area >= 1000000
Baltic states population
What is the total population of ('Estonia', 'Latvia', 'Lithuania')
SELECT SUM(population)
FROM world
WHERE name IN ('Estonia', 'Latvia', 'Lithuania')
Using GROUP BY and HAVING
You may want to look at these examples: Using GROUP BY and HAVING.
Counting the countries of each continent
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
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)
Counting big continents
List the continents that have a total population of at least 100 million.
SELECT continent
FROM world
GROUP BY continent
HAVING SUM(population)>= 100000000
The nobel table can be used to practice more SUM and COUNT functions.
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