Add column in magento install/upgrade script

For adding a new column to table in magento installer you have to add to your install/upgrade script:

$installer = $this;
$installer->startSetup();
// ...
$installer->getConnection()->addColumn(
    $this->getTable('sales/quote_payment'),
    'billing_code', // column name
    'VARCHAR(255) NOT NULL' // type definition
);
// ...
$installer->endSetup();