Why we need migrations

current.php

<?php
// What we do now
function database_update_info()
{
	return array(
		'3.0.10'	=> array(),
		// No changes from 3.0.9 to 3.0.10
		'3.0.11'	=> array(),
			'add_columns'		=> array(
				PROFILE_FIELDS_TABLE			=> array(
					'field_show_novalue'		=> array('BOOL', 0),
				),
			),
		'3.1.0'		=> array(),
		'3.1.1'	=> array(
			'add_columns'		=> array(
				PROFILE_FIELDS_TABLE			=> array(
					'field_show_novalue'		=> array('BOOL', 0),
				),
			),
		);
}

Version20121001151649.php

<?php
// A migration file, one of these would be created every time someone changes their db (so multiple times a feature or once for a feature). Then all of these migration files that have not yet been applied (DB keeps track of migrations applied) would be applied.
class Version20121001151649 extends AbstractMigration
{
    public function up(Schema $schema)
    {
        $this->addSql("QUERY");
    }

    public function down(Schema $schema)
    {
        $this->addSql("QUERY");
    }
}