Using Drush to upgrade Drupal
The function drush_sql_empty_db() has been removed in Drush 7.  You have two choices:


Downgrade to Drush 6 (it is possible to install Drush 6 at a different location, and alias 'drush6' to point to the older version).
Fix the site upgrade command.


The equivalent function to drush_sql_empty_db() in Drush 7 is:

$sql = drush_sql_get_class();
$sql-&gt;drop_or_create();


There may be other issues with Drush site-upgrade and Drush 7; I have not tried it in a while.