Difference between revisions of "SELECT basics"

Revision as of 14:15, 6 July 2012

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

@@ Line 77: / Line 77: @@
 <div class='qu'>
 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'>
 SELECT name , region