SQL Query to find number of mutual friends given a table of person, friend pair

Question

I have searched for other questions and I was able to solve part of what I wanted but I couldn\'t get any further from that.

I have a table with two columns(user, friend

Answer 1

You can use a self-join:

select f1.user as user1, f2.user as user2, count(*) as num_in_common
from friends f1 join
     friends f2
     on f1.friend = f2.friend 
group by f1.user, f2.user;

You can add a where clause if you want this information for a particular pair of users.