Question

I’m currently trying to design the database for a simple social site. I’m using MySQL for my database. Currently, I only have a users table. Basically, I want users to be able to add friends and be able to list their friends. I’m thinking of creating a friends table, something like:

friends table
user_id
friend_id

And whenever someone adds a friend, it will create an entry. I’m not exactly sure if I’m on the right direction. Another question, is there a way to retrieve all 2nd degree friends?(friends of friends) Any help would be appreciated. Thanks a lot in advance!

Answer 1

Yes, you’re on the right path.

You can retrieve 2nd degree friends by joining the friends table to itself

select t2.friend_id
from friends t1 
     inner join friends t2 on t1.friend_id = t2.user_id
where t1.user_id = ...

One thing to consider is commutativity – if A is a friend of B, is B a friend of A ?