How to write select statement for find friends( like facebook find friends concept) ?

Question

Hi,

I have two tables 
1.User table - UserId is primary key
2.Friends table - FriendsId is primary keys

In User table I have all users list

I want to get records from following relation

User->Friend->SubFriend

User has some Friends and

Each Friend has some subfriends

requirement:

How to write select statement for get all subfriends list,

Thank you in advance