Can I use Wordpress to register a User and write custom database application to retrieve and write a user data from a database during a log-in session?
For example, select all the rows of data from a database where user id= registered user? Write the rows of a database where user id=registered user?

I understand it might involve other web framework Ruby/Rails or ASP .net MVC, but I prefer to use Wordpress or Joomla due to its extensible support of CMS add-on, but I am not sure if they support custom database application as described above.

thanks for you help.