如何使用SQL或Sphinx查找相关的带标记的记录

Story.find(1).find_related_tags

stories:
  id
  content

tags:
  id
  name

story_tags:
  story_id
  tag_id

SELECT stories.id, COUNT(*) AS ordering FROM stories 
  INNER JOIN story_tags ON story_tags.story_id = stories.id 
  WHERE story_tags.tag_id IN (\'id of tag a\', \'id of tag b\', \'id of tag c\', \'id of tag d\') 
  GROUP BY stories.id
  ORDER BY ordering DESC;

class MyModel < ActiveRecord::Base

  scope :related_to, lambda { |record|
    joins(:tags,:taggings).
    where(record.class.model_name == self.model_name ? [\"#{table_name}.id != ?\", record.id] : \"\").
    where(\"tags.id IN (SELECT taggings.tag_id from taggings where taggable_type = ? and taggable_id = ?)\", record.class.model_name, record.id).
    order(\"count(DISTINCT(tags.id)) DESC\").
    group(\"#{table_name}.id\")
  }

end