Get authenticated user details from a remote database I have 2 domains say site1.com and example.com. I have separate databases for both these sites . 

How could I perform or allow users from my site1.com to login to my second site example.com without registering. If a person is an authenticated user in site1.com, he or she could login to the example.com site without signing up, i.e by using the login credentials of site1.com. Are there any modules that would help or be suitable for my task?

Also I would like to know is I could access some table details from a remote database. Thanks in advance
I recommend separating these questions.

1) Drupal Single Sign on module: https://drupal.org/project/sso

2) Again, I recommend posting this as a separate question, but could you be more specific? which table(s)?