To store the customer choice for their relay point, we will first have to create a MySQL table to save the association between the chosen relay point and the customer's cart.

In your module's root directory, create a new directory named install. In this directory, create one file named install.sql; this file will contain the new table creation:

CREATE TABLE IF NOT EXISTS `PREFIX_mymod_carrier_cart` (
  `id_mymod_carrier_cart` int(11) NOT NULL AUTO_INCREMENT,
  `id_cart` int(11) NOT NULL,
  `relay_point` text NOT NULL,
  `date_add` datetime NOT NULL,
  PRIMARY KEY (`id_mymod_carrier_cart`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

Then, in our module's main class, we will add the loadSQLFile method that we used in a previous chapter:

public...