Difference between revisions of "SELECT Reference"

Latest revision as of 10:11, 13 April 2013

SELECT Operations

Concatenate Columns

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'

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

@@ Line 1: / Line 1: @@
-CREATE TABLE test_image
+{{SELECT Ref}}
- (
+The [[SELECT]] command is used to show data from a database.
- ID NUMBER,
-  image_filename VARCHAR2(50),
+The output from a SELECT statement is always a grid - with a number of rows and a number of columns.
- image BLOB
+==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>Mexico</td><td class="r">106400000</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 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]]