Difference between revisions of "SQLZOO:SELECT basics"

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(Introducing the BBC Table of Countries)
(Introducing the BBC Table of Countries)
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<div class='qu'>
 
<div class='qu'>
 
Where to find some very small, very rich countries.<br/>
 
Where to find some very small, very rich countries.<br/>
  <b>We use <code>AND</code> to ensure that two or more conditions hold
+
<b>We use <code>AND</code> to ensure that two or more conditions hold
  true.</b>
+
true.</b>
  <div>The example shows the countries where the population is small and the
+
<div>The example shows the countries where the population is small and the
  gdp is high.</div>
+
gdp is high.</div>
  <div class='imper'>Show the <b>name</b> and <b>region</b> where the area is less then 2000 and the gdp is more than 5000000000</div>
+
<div class='imper'>Show the <b>name</b> and <b>region</b> where the area is less then 2000 and the gdp is more than 5000000000</div>
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
 
SELECT name , region
 
SELECT name , region

Revision as of 14:15, 6 July 2012

Introducing the BBC Table of Countries

This tutorial introduces SQL as a query language. We will be using the SELECT command on the table bbc:

name region area population gdp
Afghanistan South Asia 652225 26000000
Albania Europe 28728 3200000 6656000000
Algeria Middle East 2400000 32900000 75012000000
Andorra Europe 468 64000
...

The example shows the population of 'France'. Strings should be in 'single quotes';

Show the population of Germany

SELECT population FROM bbc
  WHERE name = 'France'
SELECT population FROM bbc
  WHERE name = 'Germany'
This query shows the population density population/area for each country where the area is over 5,000,000 km2.
Show the per capita gdp: gdp/population for each country where the area is over 5,000,000 km2
SELECT name, population/area FROM bbc
  WHERE area > 5000000
SELECT name, gdp/population FROM bbc
  WHERE area > 5000000

Where to find some very small, very rich countries.
We use AND to ensure that two or more conditions hold true.

The example shows the countries where the population is small and the gdp is high.
Show the name and region where the area is less then 2000 and the gdp is more than 5000000000
SELECT name , region
  FROM bbc
  WHERE population < 2000000
    AND gdp > 5000000000
SELECT name , region
  FROM bbc
  WHERE area < 2000
    AND gdp > 5000000000
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