Difference between revisions of "SELECT Reference"

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How to read data
 
 
{{SELECT Ref}}
 
{{SELECT Ref}}
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The [[SELECT]] command is used to show data from a database.
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The output from a SELECT statement is always a grid - with a number of rows and a number of columns.
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==Simple SELECT==
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The simplest SELECT commands involve a single table:
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<table>
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<tr><th>SQL</th><th>Result</th></tr>
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<tr><td>
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<source lang='sql'>
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SELECT name, population
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  FROM bbc
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WHERE region='North America'
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</source>
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</td><td>
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<table class="sqlmine"><tr><th>name</th><th>population</th></tr><tr><td>Canada</td><td class="r">32000000</td></tr><tr><td>Mexico</td><td class="r">106400000</td></tr><tr><td>United States of America</td><td class="r">295000000</td></tr></table>
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</td></tr></table>
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*The SELECT line determines which columns to show - in this case <code>name</code> and <code>population</code>, both of which are columns of the bbc table.
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*The WHERE clause determines which rows to show
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*The SELECT statement may involve data from more than one table using a [[JOIN]] or a [[UNION]].
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*SELECT statements may nested - that is the output from one SELECT may be the input to another SELECT.
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*The output from a SELECT may be added to another table using [[INSERT .. SELECT]]

Revision as of 11:48, 18 June 2013

The SELECT command is used to show data from a database.

The output from a SELECT statement is always a grid - with a number of rows and a number of columns.

Simple SELECT

The simplest SELECT commands involve a single table:

SQLResult
SELECT name, population
  FROM bbc
 WHERE region='North America'
namepopulation
Canada32000000
Mexico106400000
United States of America295000000
  • The SELECT line determines which columns to show - in this case name and population, both of which are columns of the bbc table.
  • The WHERE clause determines which rows to show
  • The SELECT statement may involve data from more than one table using a JOIN or a UNION.
  • SELECT statements may nested - that is the output from one SELECT may be the input to another SELECT.
  • The output from a SELECT may be added to another table using INSERT .. SELECT
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