Add Column to existing Table

Table Name: ism_storelocator/location
Setup Script name: mysql4-upgrade-1.0.10-1.0.11.php

<?php$installer = $this;

$installer->startSetup();

$installer->getConnection()->addColumn(
    $this->getTable('ism_storelocator/location'),
    'default_url',
    'varchar(200)');

$installer->endSetup();