Active records - "smart" select

[eluser]ibnclaudius[/eluser]
Sorry for the wait. Still not that, you are only selecting and ordering the communities by the number of followers it has. I want to suggest communities that a user may want to follow.

For example:

Communities: 1,2,3,4,5,6,7,8,9,10,11,12,13,14

User A follows: 1,2,3,10,11,12,13,14

User B follows: 1,2,4,10,11,12,13,14

User H follows: 1,4,8

User C follows: 5,6,7
User D follows: 5,6,7
User E follows: 5,6,7
User F follows: 5,6,7
User G follows: 5,6,7
User I follows: 5,6,7
User J follows: 5,6,7

Let's suggest the user A the the communities he may want to follow ordered by this "may" param, in this case would be:

4,8,5,6,7,9

I've done part of it. The problem is that it doesn't return communities that hasn't at least one user that follow another community as user A. In this case, my query would return only:

4,8

SQL Fiddle:
http://bit.ly/MF9Lve