Difference between revisions of "SELECT basics"

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#REDIRECT [[SQLZOO:SELECT basics]]
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{{Languages}}
 +
<div class="ref_section">
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<table class='db_ref'>
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<tr><th>name</th><th>continent</th><th>area</th>
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<th>population</th><th>gdp</th></tr>
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<tr><td>Afghanistan</td><td>Asia</td><td class="r">652230</td><td class="r">25500100</td><td class="r">20343000000</td></tr>
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<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>
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<td>Angola</td><td>Africa</td><td class="r">1246700 </td><td class="r">20609294 </td><td class="r">100990000000 </td></tr>
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<tr>
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<td colspan='5'>....</td>
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</tr>
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</table>
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</div>
 +
==Introducing the <code>world</code> table of countries==
 +
  <p>This  tutorial introduces SQL. We will be using the SELECT command on the table '''world''':</p>
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 +
<div class="progress_panel"><div>
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  <div class="summary">Summary</div>
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  <div class="progressbarbg">
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    <div class="progressbar"></div>
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  </div>
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</div></div>
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 +
  <div class='extra_space' style='width:1em; height:6em;'></div>
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<div class='qu'>
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The example uses a WHERE clause to show the population of 'France'.
 +
Note that strings (pieces of text that are data) should be in 'single quotes';
 +
 
 +
<p class='imper'>Modify it to show the population of Germany</p>
 +
 
 +
<source lang='sql' class='def'>
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SELECT population FROM world
 +
  WHERE name = 'France'
 +
</source>
 +
 
 +
<source lang='sql' class='ans'>
 +
SELECT population FROM world
 +
  WHERE name = 'Germany'
 +
</source>
 +
</div>
 +
 
 +
==Per Capita GDP==
 +
<div class='qu'>
 +
<div>The query shows the name and population density
 +
for each country where the area is over 5,000,000 km<sup>2</sup>. Population density is not a column in the World table, but we
 +
can calculate it as <code>population/area</code>.</div>
 +
<div class='imper'>Modify it to show the name and per capita gdp: <code>gdp/population</code>
 +
for each country where the area is over 5,000,000 km<sup>2</sup></div>.
 +
 
 +
<source lang='sql' class='def'>
 +
SELECT name, population/area FROM world
 +
  WHERE area > 5000000
 +
</source>
 +
 
 +
<source lang='sql' class='ans'>
 +
SELECT name, gdp/population FROM world
 +
  WHERE area > '5000000'
 +
</source>
 +
 
 +
</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 'Luxembourg', 'Mauritius' and 'Samoa'.
 +
<div class='imper'>Show the '''name''' and the '''population''' for 'Ireland', 'Iceland' and 'Denmark'.</div>
 +
 
 +
 
 +
<source lang='sql' class='def'>
 +
SELECT name, population FROM world
 +
  WHERE name IN ('Luxembourg', 'Mauritius', 'Samoa');
 +
</source>
 +
 
 +
<source lang='sql' class='ans'>
 +
SELECT name, population FROM world
 +
  WHERE name IN ('Ireland', 'Iceland', 'Denmark');
 +
</source>
 +
</div>
 +
 
 +
<div> 
 +
<p><div class="quizlink">[[SELECT Quiz]]</div></p>
 +
</div>
 +
 
 +
<div class='quizlink'>[http://socweb8.napier.ac.uk/~40052114/regex/index.php?title=How_To_Play Try the regular expressions game.]</div>
 +
 
 +
<p>You are ready for tutorial one:[[SELECT_from_WORLD_Tutorial |SELECT statements with WHERE.]]</p>
 +
 
 +
 
 +
{{Languages}}
 +
 
 +
==Just the right size==
 +
<div class='qu'>
 +
Which countries are not too small and not too big?
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<code>BETWEEN</code> allows range checking (range specified is inclusive of boundary values). The example below shows countries with an area of 250,000-300,000 sq. km. Modify it to show the country and the area for countries with an area between 200,000 and 250,000.
 +
 
 +
<source lang='sql' class='def'>
 +
SELECT name, area FROM world
 +
  WHERE area BETWEEN 250000 AND 300000
 +
</source>
 +
 
 +
 
 +
<source lang='sql' class='ans'>
 +
SELECT name, area FROM world
 +
  WHERE area BETWEEN 200000 AND 250000
 +
</source>
 +
 
 +
</div>
 +
 
 +
 
 +
<p>You are ready for tutorial one:[[SELECT_from_WORLD_Tutorial |SELECT statements with WHERE.]]</p>
 +
 
 +
 
 +
{{Languages}}

Revision as of 11:44, 25 May 2016

Language: English  • Deutsch • 中文
namecontinentarea populationgdp
AfghanistanAsia6522302550010020343000000
AlbaniaEurope28748 2831741 12960000000
AlgeriaAfrica2381741 37100000 188681000000
AndorraEurope46878115 3712000000
AngolaAfrica1246700 20609294 100990000000
....

Introducing the world table of countries

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

Summary

The example uses a WHERE clause to show the population of 'France'. Note that strings (pieces of text that are data) should be in 'single quotes';

Modify it to show the population of Germany

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

Per Capita GDP

The query shows the name and population density

for each country where the area is over 5,000,000 km2. Population density is not a column in the World table, but we

can calculate it as population/area.
Modify it to show the name and 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'

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 'Luxembourg', 'Mauritius' and 'Samoa'.

Show the name and the population for 'Ireland', 'Iceland' and 'Denmark'.


SELECT name, population FROM world
  WHERE name IN ('Luxembourg', 'Mauritius', 'Samoa');
SELECT name, population FROM world
  WHERE name IN ('Ireland', 'Iceland', 'Denmark');

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


Language: English  • Deutsch • 中文

Just the right size

Which countries are not too small and not too big? BETWEEN allows range checking (range specified is inclusive of boundary values). The example below shows countries with an area of 250,000-300,000 sq. km. Modify it to show the country and the area for countries with an area between 200,000 and 250,000.

SELECT name, area FROM world
  WHERE area BETWEEN 250000 AND 300000


SELECT name, area FROM world
  WHERE area BETWEEN 200000 AND 250000


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


Language: English  • Deutsch • 中文