mysql4-upgrade-1.2.0-1.3.0.php

$installer = $this;

$installer->startSetup();
$installer->addAttribute(Mage_Catalog_Model_Product::ENTITY, 'brand', array(
						'group'			  			 => 'General', 
						'attribute_set'				 => 'Default',
						'type'						 => 'int',
						'label'						 => 'Brand',
						'input'						 => 'select',
						'required'					 => false,
						'user_defined'				 => true,
						'searchable'				 => true,
						'filterable'				 => true,
						'comparable'				 => true,
						'visible_in_advanced_search' => true,
						'default'					 => '',
						'visible'	 		 		 => true,
						'visible_on_front'			 => true,
						'filterable_in_search'	 	 => true,
						'used_in_product_listing'	 => true,
						'used_for_sort_by'			 => true,
						'is_html_allowed_on_front'	 => true,
));
$installer->endSetup();