Add a mysql setup file inside the directory of your module YourNamespace/YourModule/sql/yourmodule_setup/ and write the following code in your module’s mysql setup file:
$installer = $this;
$setup = new Mage_Eav_Model_Entity_Setup('core_setup');
$installer->startSetup();
$setup->addAttribute('catalog_category', 'my_attribute', array(
'group' => 'General',
'input' => 'text',
'type' => 'varchar',
'label' => 'My Attribute',
'backend' => '',
'frontend' => '',
'visible' => 1,
'required' => 0,
'user_defined' => 1,
'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
'visible_on_front' => 1,
'unique' => 0,
));
// add attribute to group
$installer->addAttributeToGroup('catalog_category', 'Default', 'my_module', 'my_attribute');
$installer->endSetup();
Now you found the code my_attribute and the label My Attribute. You can find it under Admin Panel / Catalog / Manage Categories / General Information .
With the array param ’sort_order‘ you can define the order in the backend-list.