I have a table friends, which contains the following columns: 
friend\_id and friend\_of (both are storing unique user ids)
lets say the table friends contains the following data:

```
friend_id   |   friend_of
-------------------------
   123      |     456    
   456      |     789    
   456      |     123

```

So this means that:  

user with id=123 have one friend with id=456  

user with id=456 have two friends with ids=123 (friend\_1) & 789(friend\_2)  

user with id=789 have one friwnd with id=456

I want to write a query that given a single user id shows every friend that this user has (with their ids).

For example:  

if given user with id=123 the output would be users with ids=456  

if given user with id=789 the output would be users with ids=456  

if given user with id=456 the output would be users with ids=123 and 789

Can you help me with the query I need?