Difference between revisions of "SQLZOO: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> | ||
| Line 45: | Line 45: | ||
==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> | ||
| − | 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>. |
<source lang='sql' class='def'> | <source lang='sql' class='def'> | ||
Revision as of 22:30, 26 June 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
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'
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
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
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')
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%'
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.
| Language: | English |
|---|
