Difference between revisions of "SUM and COUNT"

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<p>[[Using GROUP BY and HAVING.]]</p>
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==Using GROUP BY and HAVING==
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<p>You may want to look at these examples: [[Using GROUP BY and HAVING.]]</p>
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==Counting the countries of each continent==
 
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For each '''continent''' show the '''continent''' and number of countries.   
 
For each '''continent''' show the '''continent''' and number of countries.   
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==Counting big countries in each continent==
 
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For each '''continent''' show the '''continent''' and number of countries with populations of at least 10 million.   
 
For each '''continent''' show the '''continent''' and number of countries with populations of at least 10 million.   
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==Counting big continents==
 
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List the continents that '''have''' a total population of at least 100 million.   
 
List the continents that '''have''' a total population of at least 100 million.   
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<div class="lsclear">Clear your results</div>
 
  
 
<p><div class="quizlink">[[SUM and COUNT Quiz]]</div></p>
 
<p><div class="quizlink">[[SUM and COUNT Quiz]]</div></p>
 
<p>[[The nobel table can be used to practice more SUM and COUNT functions.]]</p>
 
<p>[[The nobel table can be used to practice more SUM and COUNT functions.]]</p>
 
<p>[[The_JOIN_operation |The next tutorial looks at the Table Tennis database. It shows how queries may use records from two related tables.]]
 
<p>[[The_JOIN_operation |The next tutorial looks at the Table Tennis database. It shows how queries may use records from two related tables.]]

Latest revision as of 20:38, 22 February 2017

Language: English  • 中文

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.

namecontinentarea populationgdp
AfghanistanAsia6522302550010020343000000
AlbaniaEurope28748 2831741 12960000000
AlgeriaAfrica2381741 37100000 188681000000
AndorraEurope46878115 3712000000
AngolaAfrica1246700 20609294 100990000000
...

You might want to look at these examples first

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.

The next tutorial looks at the Table Tennis database. It shows how queries may use records from two related tables.