improving a friends list query : counting the mutual friends

Question

i have two tables in my database one is to keep users info (users_table ) and the other one keeps track of the friends

users_table:

id    username      avatar  
1         max       max.jpg  
2         jack      jack.jpg  

friends_table :

id    u1_id      u2_id  
1         1          2  
2         1          3  

in every user profile i show his/her friends list

here is my query

select u.id,
    u.username,
    u.avatar
from friends_table f
join users_table u on f.u1_id = u.id || f.u2_id = u.id
where u.id <> $profile_id
    and (f.u1_id = $profile_id || f.u2_id = $profile_id)

this query selects friends of the profile owner ($profile_id)

and join them with the user table to get each friend username and avatar

now i want to count the mutual friends between each friend and the profile owner is it possible to this in one query or should i do some long and probably slow query like this for each founded friend( it's just a example and it might have some syntax error ):

       foreach ( $friends_list_query_resul as $qr ){
       $friend_id = $qr['id'];

       $mutual_count = mysql_query
    ( "select count(*) from friends_table where 
    ($u1_id = $friend_id || $u2_id = $friend_id )
               && 


    ( $u1_id IN ( SELECT `u1_id`,`u2_id` from friends_table where
     ($u1_id = $profile_id || $u2_id = $profile_id ) )

||

      $u2_id IN ( SELECT `u1_id`,`u2_id` from friends_table where
     ($u1_id = $profile_id || $u2_id = $profile_id ) )


       ")
        }

Answer 1

Your first query could also be written as:

select distinct u.id,
        u.username,
        u.avatar
    from users_table u where u.id in 
        (select case when u1_id=$profile_id then u2_id else u1_id end 
        from friends_table f where case when u1_id=$profile_id 
        then u1_id else u2_id end =$profile_id);

The mutual friends query can be written as a single query in similar fashion:

select u.id, (select count(f.id) from friends f where 
    case when f.u1_id=u.id then u2_id else u1_id end in 
        (select distinct case when u1_id=$profile_id then u2_id else u1_id end 
        from friends where case when u1_id=$profile_id then u1_id else u2_id 
        end =$profile_id) 
    and u1_id=u.id or u2_id=u.id and 
    (u1_id <> $profile_id and u2_id <> $profile_id)) 
as mutual_frnds from user u where u.id <> $profile_id;

but you might want to performance test either of them before using.