adding link to magento top menu using layout update

Add link to Magento Top Menu using Layout XML update
in your custom module's  layout.xml default handle add this

      <reference name="root">
            <reference name="top.links">
                <action method="addLink" translate="label title">
                    <label>About Us</label>
                    <url>about</url>  <!-- can use full url also -->
                    <title>About Us</title>
                    <prepare>true</prepare> <!-- set true if adding base url param -->
                    <urlParams helper="core/url/getHomeUrl"/>
                </action>
            </reference>
        </reference>

Using IF-ELSE OR CASE-WHEN in Magento Collection - Expression based field by addExpressionAttributeToSelect

Using IF-ELSE OR CASE-WHEN  in Magento Collection - Expression based temporary column field  by addExpressionAttributeToSelect

Magento addExpressionAttributeToSelect  method can be used to create temporary column in
collections

$_collection = Mage::getResourceModel('sales/order_collection')
        ->addExpressionAttributeToSelect('your_temp_column', 'CASE order_id WHEN 1 THEN one ELSE TWO END ', '');

on printing sql query using getselect
echo $_collection->getSelect() ;


 the magento will create query something like this  SELECT (CASE order_id WHEN 1 THEN one ELSE TWO END) AS your_temp_column

The temproary column can be used for sorting and filtering also , please note for filtering
you need to use 'having'  instead of builtin addAttributeToFilter method.
$_collection->getSelect()->having('your_temp_column = "one" '); 

hope this helps