Difference between revisions of "SELECT Reference"

Latest revision as of 13:31, 27 February 2015

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.

The simplest SELECT commands involve a single table:

SQL

Result

SELECT name, population
  FROM bbc
 WHERE region='North America'

name	population
Canada	32000000
United States of America	295000000

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
The select statement may aggregate values using a SELECT .. GROUP BY clause

@@ Line 1: / Line 1: @@
-CREATE TABLE emp (ID NUMBER, name VARCHAR2(40));
+{{SELECT Ref}}
+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:
+<table>
+<tr><th>SQL</th><th>Result</th></tr>
+<tr><td>
+<source lang='sql'>
+SELECT name, population
+  FROM bbc
+ WHERE region='North America'
+</source>
+</td><td>
+<table class="sqlmine"><tr><th>name</th><th>population</th></tr>
+<tr><td>Canada</td><td class="r">32000000</td></tr>
+<tr><td>United States of America</td><td class="r">295000000</td></tr></table>
+</td></tr></table>
+*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.
+*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 within SELECT Tutorial|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]]
+*The select statement may aggregate values using a [[SELECT .. GROUP BY]] clause