Difference between revisions of "SELECT basics"

From SQLZOO
Jump to: navigation, search
(→‎Introducing the BBC Table of Countries)
(48 intermediate revisions by 8 users not shown)
Line 1: Line 1:
−
==Introducing the BBC Table of Countries==
+
<div class="ref_section">
−
This tutorial introduces SQL as a  query language. We will be using the SELECT command on the table bbc:
+
<table class='db_ref'>
−
<table style='' border='1'><tr>
+
<tr><th>name</th><th>continent</th><th>area</th>
−
<th>name</th>
+
<th>population</th><th>gdp</th></tr>
−
<th>region</th>
+
<tr><td>Afghanistan</td><td>Asia</td><td class="r">652230</td><td class="r">25500100</td><td class="r">20343000000</td></tr>
−
<th>area</th>
+
<tr><td>Albania</td><td>Europe</td><td class="r">28748 </td><td class="r">2831741 </td><td class="r">12960000000 </td></tr>
−
<th>population</th>
+
<tr><td>Algeria</td><td>Africa</td><td class="r">2381741 </td><td class="r">37100000 </td><td class="r">188681000000 </td></tr>
−
<th>gdp</th>
+
<tr><td>Andorra</td><td>Europe</td><td class="r">468</td><td class="r">78115 </td><td class="r">3712000000 </td></tr><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>Afghanistan</td>
+
−
<td>South Asia</td>
+
−
<td align='right'>652225</td>
+
−
<td align='right'>26000000</td>
+
−
<td></td>
+
−
</tr>
+
−
<tr>
+
−
<td>Albania</td>
+
−
<td>Europe</td>
+
−
<td align='right'>28728</td>
+
−
<td align='right'>3200000</td>
+
−
<td align='right'>6656000000</td>
+
−
</tr>
+
−
<tr>
+
−
<td>Algeria</td>
+
−
<td>Middle East</td>
+
−
<td align='right'>2400000</td>
+
−
<td align='right'>32900000</td>
+
−
<td align='right'>75012000000</td>
+
−
</tr>
+
−
<tr>
+
−
<td>Andorra</td>
+
−
<td>Europe</td>
+
−
<td align='right'>468</td>
+
−
<td align='right'>64000</td>
+
−
<td></td>
+
−
</tr>
+
 
<tr>
 
<tr>
 
<td colspan='5'>...</td>
 
<td colspan='5'>...</td>
 
</tr>
 
</tr>
 
</table>
 
</table>
 +
</div>
 +
 +
==Introducing the <code>world</code> table of countries==
 +
  <p>This tutorial introduces SQL as a  query language. We will be using the SELECT command on the table '''world''':</p>
 +
 +
<div class="progress_panel"><div>
 +
  <div class="summary">Summary</div>
 +
  <div class="progressbarbg">
 +
    <div class="progressbar"></div>
 +
  </div>
 +
</div></div>
  
 +
  <div class='extra_space' style='width:1em; height:6em;'></div>
 +
 
 
<div class='qu'>
 
<div class='qu'>
 
The example shows the population of 'France'.
 
The example shows the population of 'France'.
Line 48: Line 33:
  
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
−
SELECT population FROM bbc
+
SELECT population FROM world
 
   WHERE name = 'France'
 
   WHERE name = 'France'
 
</source>
 
</source>
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT population FROM bbc
+
SELECT population FROM world
 
   WHERE name = 'Germany'
 
   WHERE name = 'Germany'
 
</source>
 
</source>
 
</div>
 
</div>
  
 +
==Per Capita GDP==
 
<div class='qu'>
 
<div class='qu'>
 
<div>This query shows the population density <code>population/area</code>
 
<div>This query shows the population density <code>population/area</code>
Line 65: Line 51:
  
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>
−
SELECT name, population/area FROM bbc
+
SELECT name, population/area FROM world
 
   WHERE area > 5000000
 
   WHERE area > 5000000
 
</source>
 
</source>
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT name, gdp/population FROM bbc
+
SELECT name, gdp/population FROM world
 
   WHERE area > 5000000
 
   WHERE area > 5000000
 
</source>
 
</source>
 
</div>
 
</div>
  
 +
==Small and wealthy==
 
<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/>
Line 81: Line 68:
 
<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>continent</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 , continent
−
   FROM bbc
+
   FROM world
 
   WHERE population < 2000000
 
   WHERE population < 2000000
 
     AND gdp > 5000000000
 
     AND gdp > 5000000000
Line 90: Line 77:
  
 
<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
−
SELECT name , region
+
SELECT name , continent
−
   FROM bbc
+
   FROM world
 
   WHERE area < 2000
 
   WHERE area < 2000
 
     AND gdp > 5000000000
 
     AND gdp > 5000000000
 
</source>
 
</source>
 
</div>
 
</div>
 +
 +
==Scandinavia==
 +
<div class='qu'>
 +
Checking a list The word <b>IN</b> allows us to check if an item is in a list.
 +
The example shows the name and population for the countries 'Ireland', 'Iceland' and 'Denmark'
 +
<div class='imper'>Show the '''name''' and the '''population''' for 'Denmark', 'Finland', 'Norway', 'Sweden'
 +
</div>
 +
<source lang='sql' class='def'>
 +
SELECT name, population FROM world
 +
  WHERE name IN ('Ireland', 'Iceland',
 +
                'Denmark')</source>
 +
 +
<source lang='sql' class='ans'>
 +
SELECT name, population FROM world
 +
  WHERE name IN ('Denmark', 'Finland',
 +
                'Norway', 'Sweden')</source>
 +
</div>
 +
 +
==Starts with G==
 +
<div class='qu'>
 +
What are the countries beginning with G?
 +
'''The word''' <code>LIKE</code> '''permits pattern matching''' - % '''is the wildcard'''.
 +
The examples shows countries beginning with D
 +
<div class='imper'>Show each country that begins with G</div>
 +
<source lang='sql' class='def'>
 +
SELECT name FROM world
 +
  WHERE name LIKE 'D%'
 +
</source>
 +
 +
<source lang='sql' class='ans'>
 +
SELECT name FROM world
 +
  WHERE name LIKE 'G%'
 +
</source>
 +
</div>
 +
 +
==Just the right size==
 +
<div class='qu'>
 +
Which countries are not too small and not too big?
 +
<code>BETWEEN</code> allows range checking - note that it is inclusive.
 +
<div class='imper'>'''Show the area in 1000 square km. Show''' ''area''/1000 '''instead of''' ''area''</div>
 +
<source lang='sql' class='def'>
 +
SELECT name, area FROM world
 +
  WHERE area BETWEEN 207600 AND 244820
 +
</source>
 +
 +
<source lang='sql' class='ans'>
 +
SELECT name, area/1000 FROM world
 +
  WHERE area BETWEEN 207600 AND 244820
 +
</source>
 +
</div>
 +
 +
<div>
 +
<div class="lsclear">Clear your results</div>
 +
<p><div class="quizlink">[[SELECT Quiz]]</div></p>
 +
</div>
 +
<p>You are ready for tutorial one:[[SELECT_from_WORLD_Tutorial |SELECT statements with WHERE.]]</p>
 +
 +
 +
{{Languages}}

Revision as of 02:02, 17 February 2013

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

Contents

Introducing the world table of countries

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

Summary

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

Show the population of Germany

SELECT population FROM world
  WHERE name = 'France'
SELECT population FROM world
  WHERE name = 'Germany'

Per Capita GDP

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 world
  WHERE area > 5000000
SELECT name, gdp/population FROM world
  WHERE area > 5000000

Small and wealthy

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 continent where the area is less then 2000 and the gdp is more than 5000000000
SELECT name , continent
  FROM world
  WHERE population < 2000000
    AND gdp > 5000000000
SELECT name , continent
  FROM world
  WHERE area < 2000
    AND gdp > 5000000000

Scandinavia

Checking a list The word IN allows us to check if an item is in a list. The example shows the name and population for the countries 'Ireland', 'Iceland' and 'Denmark'

Show the name and the population for 'Denmark', 'Finland', 'Norway', 'Sweden' 
SELECT name, population FROM world
  WHERE name IN ('Ireland', 'Iceland',
                 'Denmark')
SELECT name, population FROM world
  WHERE name IN ('Denmark', 'Finland',
                 'Norway', 'Sweden')

Starts with G

What are the countries beginning with G? The word LIKE permits pattern matching - % is the wildcard. The examples shows countries beginning with D

Show each country that begins with G
SELECT name FROM world
  WHERE name LIKE 'D%'
SELECT name FROM world
  WHERE name LIKE 'G%'

Just the right size

Which countries are not too small and not too big? BETWEEN allows range checking - note that it is inclusive.

Show the area in 1000 square km. Show area/1000 instead of area
SELECT name, area FROM world
  WHERE area BETWEEN 207600 AND 244820
SELECT name, area/1000 FROM world
  WHERE area BETWEEN 207600 AND 244820
Clear your results

SELECT Quiz

You are ready for tutorial one:SELECT statements with WHERE.


Language: English  • Deutsch
Retrieved from "http://sqlzoo.net/w/index.php?title=SELECT_basics&oldid=8731"
Personal tools
Namespaces

Variants
Actions
Reference
Toolbox
Google AdSense