Difference between revisions of "SUM and COUNT"

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<h3>BBC Country Profile: Aggregate functions</h3>
+
<h3>World Country Profile: Aggregate functions</h3>
 
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.
 
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.
 +
<div class="ref_section">
 +
<table class='db_ref'>
 +
<tr><th>name</th><th>continent</th><th>area</th>
 +
<th>population</th><th>gdp</th></tr>
 +
<tr><td>Afghanistan</td><td>Asia</td><td class="r">652230</td><td class="r">25500100</td><td class="r">20343000000</td></tr>
 +
<tr><td>Albania</td><td>Europe</td><td class="r">28748 </td><td class="r">2831741 </td><td class="r">12960000000 </td></tr>
 +
<tr><td>Algeria</td><td>Africa</td><td class="r">2381741 </td><td class="r">37100000 </td><td class="r">188681000000 </td></tr>
 +
<tr><td>Andorra</td><td>Europe</td><td class="r">468</td><td class="r">78115 </td><td class="r">3712000000 </td></tr><tr>
 +
<td>Angola</td><td>Africa</td><td class="r">1246700 </td><td class="r">20609294 </td><td class="r">100990000000 </td></tr>
 +
<tr>
 +
<td colspan='5'>...</td>
 +
</tr>
 +
</table>
 +
</div>
  
 
<h2>Exercises</h2>
 
<h2>Exercises</h2>
 
<p>[[Using SUM, Count, MAX, DISTINCT and ORDER BY]].</p>
 
<p>[[Using SUM, Count, MAX, DISTINCT and ORDER BY]].</p>
 +
 +
<div class="progress_panel"><div>
 +
  <div class="summary">Summary</div>
 +
  <div class="progressbarbg">
 +
    <div class="progressbar"></div>
 +
  </div>
 +
</div></div>
 +
 
<div class='qu'>
 
<div class='qu'>
−
Show the total '''population''' of the world.                                    
+
Show the total '''population''' of the world.
−
  bbc('''name''', '''region''', '''area''', '''population''', '''gdp''')
+
 
 +
                               
 +
  world('''name''', '''continent''', '''area''', '''population''', '''gdp''')
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
 
SELECT SUM(population)
 
SELECT SUM(population)
−
FROM bbc
+
FROM world
 
</source>
 
</source>
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
 
SELECT SUM(population)
 
SELECT SUM(population)
−
FROM bbc
+
FROM world
 
</source>
 
</source>
 
</div>
 
</div>
  
 
<div class='qu'>
 
<div class='qu'>
−
List all the regions - just once each.  
+
List all the continents - just once each.  
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
 
</source>
 
</source>
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT DISTINCT(region)
+
SELECT DISTINCT(continent)
−
FROM bbc
+
FROM world
 
</source>
 
</source>
 
</div>
 
</div>
Line 36: Line 60:
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
 
SELECT SUM(gdp)
 
SELECT SUM(gdp)
−
FROM bbc
+
FROM world
−
WHERE region = 'Africa'
+
WHERE continent = 'Africa'
 
</source>
 
</source>
 
</div>
 
</div>
Line 47: Line 71:
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT COUNT(region)
+
SELECT COUNT(name)
−
FROM bbc
+
FROM world
 
WHERE area >= 1000000
 
WHERE area >= 1000000
 
</source>
 
</source>
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<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
 
SELECT SUM(population)
 
SELECT SUM(population)
−
FROM bbc
+
FROM world
 
WHERE name IN('France','Germany','Spain')  
 
WHERE name IN('France','Germany','Spain')  
 
</source>
 
</source>
Line 67: Line 91:
 
<p>[[Using GROUP BY and HAVING.]]</p>
 
<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 '''continent''' show the '''continent''' and number of countries.   
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
 
</source>
 
</source>
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT region, COUNT(name)
+
SELECT continent, COUNT(name)
−
FROM bbc
+
FROM world
−
GROUP BY(region)
+
GROUP BY(continent)
 
</source>
 
</source>
 
</div>
 
</div>
  
 
<div class='qu'>
 
<div class='qu'>
−
For each '''region''' show the '''region''' 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.   
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
 
</source>
 
</source>
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT region, COUNT(name)
+
SELECT continent, COUNT(name)
−
FROM bbc
+
FROM world
 
WHERE population >= 10000000
 
WHERE population >= 10000000
−
GROUP BY(region)
+
GROUP BY(continent)
 
</source>
 
</source>
 
</div>
 
</div>
  
 
<div class='qu'>
 
<div class='qu'>
−
List the regions with total populations of at least 100 million.   
+
List the continents with total populations of at least 100 million.   
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
 
</source>
 
</source>
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT region
+
SELECT continent
−
FROM bbc
+
FROM world
−
GROUP BY region
+
GROUP BY continent
 
HAVING SUM(population)>= 100000000
 
HAVING SUM(population)>= 100000000
 
</source>
 
</source>
 
</div>
 
</div>
  
−
<h2>What next</h2>
+
<div class="lsclear">Clear your results</div>
 +
 
 +
<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 is looks at the Table Tennis database. It shows how queries may use records from two related tables.]]
 
<p>[[The_JOIN_operation |The next tutorial is looks at the Table Tennis database. It shows how queries may use records from two related tables.]]

Latest revision as of 23:04, 8 December 2012

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
...

Exercises

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

Summary

Show the total population of the world. 


world(name, continent, area, population, gdp)

SELECT SUM(population)
FROM world
SELECT SUM(population)
FROM world

List all the continents - just once each. 

 
SELECT DISTINCT(continent)
FROM world

Give the total GDP of Africa 

 
SELECT SUM(gdp)
FROM world
WHERE continent = 'Africa'

How many countries have an area of at least 1000000 

 
SELECT COUNT(name)
FROM world
WHERE area >= 1000000

What is the total population of ('France','Germany','Spain') 

 
SELECT SUM(population)
FROM world
WHERE name IN('France','Germany','Spain')

Using GROUP BY and HAVING.

For each continent show the continent and number of countries. 

 
SELECT continent, COUNT(name)
FROM world
GROUP BY(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)

List the continents with total populations of at least 100 million. 

 
SELECT continent
FROM world
GROUP BY continent
HAVING SUM(population)>= 100000000
Clear your results

SUM and COUNT Quiz

The nobel table can be used to practice more SUM and COUNT functions.

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

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