Difference between revisions of "SELECT basics"
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==Introducing the <code>world</code> table of countries== | ==Introducing the <code>world</code> table of countries== | ||
| − | <p>This tutorial introduces SQL | + | <p>This tutorial introduces SQL. We will be using the SELECT command on the table '''world''':</p> |
<div class="progress_panel"><div> | <div class="progress_panel"><div> | ||
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==Per Capita GDP== | ==Per Capita GDP== | ||
<div class='qu'> | <div class='qu'> | ||
| − | <div> | + | <div>The query shows the population density <code>population/area</code> |
for each country where the area is over 5,000,000 km<sup>2</sup>.</div> | for each country where the area is over 5,000,000 km<sup>2</sup>.</div> | ||
<div class='imper'>Show the per capita gdp: <code>gdp/population</code> | <div class='imper'>Show the per capita gdp: <code>gdp/population</code> | ||
Latest revision as of 14:32, 29 April 2013
| name | continent | area | population | gdp |
|---|---|---|---|---|
| Afghanistan | Asia | 652230 | 25500100 | 20343000000 |
| Albania | Europe | 28748 | 2831741 | 12960000000 |
| Algeria | Africa | 2381741 | 37100000 | 188681000000 |
| Andorra | Europe | 468 | 78115 | 3712000000 |
| Angola | Africa | 1246700 | 20609294 | 100990000000 |
| ... | ||||
Contents |
[edit] Introducing the world table of countries
This tutorial introduces SQL. We will be using the SELECT command on the table world:
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'
[edit] Per Capita GDP
population/area
for each country where the area is over 5,000,000 km2.gdp/population
for each country where the area is over 5,000,000 km2SELECT name, population/area FROM world WHERE area > 5000000
SELECT name, gdp/population FROM world WHERE area > 5000000
[edit] Small and wealthy
Where to find some very small, very rich countries.
We use AND to ensure that two or more conditions hold
true.
SELECT name , continent FROM world WHERE population < 2000000 AND gdp > 5000000000
SELECT name , continent FROM world WHERE area < 2000 AND gdp > 5000000000
[edit]
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'
SELECT name, population FROM world WHERE name IN ('Ireland', 'Iceland', 'Denmark')
SELECT name, population FROM world WHERE name IN ('Denmark', 'Finland', 'Norway', 'Sweden')
[edit] 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
SELECT name FROM world WHERE name LIKE 'D%'
SELECT name FROM world WHERE name LIKE 'G%'
[edit] Just the right size
Which countries are not too small and not too big?
BETWEEN allows range checking - note that it is inclusive.
SELECT name, area FROM world WHERE area BETWEEN 207600 AND 244820
SELECT name, area/1000 FROM world WHERE area BETWEEN 207600 AND 244820
You are ready for tutorial one:SELECT statements with WHERE.
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