Re: slow self-join query

@merlin, @kevin: Thank you both -- I'll try your suggestions as soon
as I get back to the mothership.

@kevin: I hear you. (I'm deeply steeped in Ruby on Rails and
foolishly assume that it's easy to read.) With that in mind:

\d user_associations
Table "public.user_associations"
Column | Type |
Modifiers
-------------+-----------------------------+---------------------------------------------------------
id | integer | not null default
nextval('followings_id_seq'::regclass)
leader_id | integer |
follower_id | integer |
created_at | timestamp without time zone | not null
updated_at | timestamp without time zone | not null
Indexes:
"followings_pkey" PRIMARY KEY, btree (id)
"index_followings_on_leader_id_and_follower_id" UNIQUE, btree
(leader_id, follower_id)
"index_followings_on_follower_id" btree (follower_id)
"index_followings_on_leader_id" btree (leader_id)