Собственно, сократив:
SELECT calendar.*
FROM calendar AS c
LEFT JOIN subscribes_fields AS f
ON c.id_object = f.id_field
AND f.id_follower = 1
AND c.type = 'field'
LEFT JOIN subscribes_user_teams AS t
ON c.id_object = t.id_team
AND t.id_follower = 1
AND c.type = 'team'
LEFT JOIN subscribes_events AS e
ON c.id = e.id_event
AND e.id_follower = 1
AND e.type = 'user'
WHERE ((f.id IS NOT NULL OR f.id_field IS NOT NULL)
OR (t.id IS NOT NULL OR t.id_team IS NOT NULL))
AND c.d_start = 17
AND c.m_start = 11
AND c.y_start = 2012
