Storing follow relationships

We've now created two tables, each of which allows us to answer two important questions about follow relationships: first, whom a user follows; and second, who follows a user. Now let's establish some follow relationships.

For now, let's have alice follow a couple of other users, bob and carol:

INSERT INTO "user_outbound_follows" 
  ("follower_username", "followed_username") 
VALUES ('alice', 'bob'); 
INSERT INTO "user_inbound_follows" 
  ("followed_username", "follower_username") 
VALUES ('bob', 'alice'); 
INSERT INTO "user_outbound_follows" 
  ("follower_username", "followed_username") 
VALUES ('alice', 'carol'); 
INSERT INTO "user_inbound_follows" 
  ("followed_username", "follower_username") 
VALUES ('carol', 'alice');

For each follow relationship, we have to insert two rows: one in the user_outbound_follows table to store the relationship from the perspective of the follower, and one in the user_inbound_follows table to store the relationship from the perspective...