Example

$database =& JFactory::getDBO();

$sql = "SELECT * FROM #__categories WHERE section = 4";
$database->setQuery( $sql );
$categories = $database->loadRowList( 2 );
print_r( $categories );

Result

Array
(
    [The CMS] => Array
        (
            [0] => 29
            [1] => 0
            [2] => The CMS
            [3] => The CMS
            [4] => 
            [5] => 4
            [6] => left
            [7] => Information about the software behind Joomla!<br />
            [8] => 1
            [9] => 0
            [10] => 0000-00-00 00:00:00
            [11] => 
            [12] => 2
            [13] => 0
            [14] => 0
            [15] => 
        )

    [The Project] => Array
        (
            [0] => 25
            [1] => 0
            [2] => The Project
            [3] => The Project
            [4] => 
            [5] => 4
            [6] => left
            [7] => General facts about Joomla!<br />
            [8] => 1
            [9] => 0
            [10] => 0000-00-00 00:00:00
            [11] => 
            [12] => 1
            [13] => 0
            [14] => 0
            [15] => 
        )

    [The Community] => Array
        (
            [0] => 30
            [1] => 0
            [2] => The Community
            [3] => The Community
            [4] => 
            [5] => 4
            [6] => left
            [7] => About the millions of Joomla! users and websites<br />

            [8] => 1
            [9] => 0
            [10] => 0000-00-00 00:00:00
            [11] => 
            [12] => 3
            [13] => 0
            [14] => 0
            [15] => 
        )

)