Question

i have a user table

 id , username
 22 , max
 33 , jack
 44 , joe

And friends table

id , u1 , u2 , status , reciver

For increasing the speed on reading the friends i’ve decided to add two row to the table for each friendship
so it goes like this

id , u1 , u2 , status , reciver

 1 , 22 , 33 ,  1     ,  22
 2 , 33 , 22 ,  1     ,  22


 3 , 22 , 44 ,  1     ,  22
 4 , 44 , 22 ,  1     ,  22

 5 , 22 , 55 ,  1     ,  22
 6 , 55 , 22 ,  1     ,  22

Now i want to get each user friends and count the mutual friends between these two like facebook

Here is my friends list query :

         $profile_id = $current_user->id;

         $res = $db->query("
            select 
            u.id as firend_id, 
            u.username  as firend_name,
            f.status    as firendship_status,
            COUNT(f3.u2)  as mutual  

            from friends f      
              JOIN users  u on f.u2 = u.id
              LEFT JOIN friends f2 on f.u2 = f2.u1 and f2.u2 != $profile_id
              LEFT JOIN friends f3 on f3.u1 = $profile_id AND f3.u2=f2.u2     
            WHERE  f.u1 = $profile_id
            group by f2.1
           ");

        echo 'friends list : '
        foreach ($res->result() as $r ){

          echo $r->firend_name;
          echo $r->mutual.' friends';

        }

so i check the owner of profile id ($profile_id) against friends.u1 and
join the friends.u2(founded friend) to the users table to get his username and id

the problem is in counting the mutual friends

I join the friends table with it self
on each founded friend

It seems ok on the paper but it returns some weird results

Like if the users has 3 friends and there is no mutual friends it return only one of the 3 friends
!

And if there is mutual friends it shows all of the friends but the mutual friends number is wrong on most cases

there is a problem with group by statement

Answer 1

You can’t do this with only 2 friends tables, you’ll need a third:

• Friends1: select friends of user $profile_id (as you have)
• Friends2: select the friends of the friend of $profile_id (as you have)
• Friends3: work out the mutual friends between the friends of the the
  friend of $profile_id and the friends of $profile_id

I’ve not tested the following and it works for my sample data – just double check on a larger sample:

        select  
        u.id as firend_id,  
        u.username  as firend_name, 
        f.status    as firendship_status, 
        COUNT(f3.u2)  as mutual 

        from friends f       
          JOIN users  u on f.u2 = u.id 
          LEFT JOIN friends f2 on f.u2 = f2.u1 and f2.u2 != $profile_id 
          LEFT JOIN friends f3 on f3.u1 = $profile_id AND f3.u2=f2.u2

        WHERE  f.u1 = $profile_id 
        group by f.u2