Importing SQL databases
The Migrate module, not to be confused with Backup &amp; Migrate, can provide this functionality. The project page says it better than I can.


  The migrate module provides a flexible framework for migrating content into Drupal from other sources (e.g., when converting a web site from another CMS to Drupal). Out-of-the-box, support for creating core Drupal objects such as nodes, users, and comments is included - it can easily be extended for migrating other kinds of content.


Deliberately, it's fairly complicated module. Here's a talk on it from DrupalCon denver