ActiveRecord多个连接并计算重复行

Question

我很难获得查询工作。查询返回重复的行。

手工计数与来自连接的计数：https://www.dropbox.com/s/sms6mot4ly6b54o/Screenshot%202014-05-09%2018.33.09.png - 第一个结果表示companies.products.count，第二个结果表示通过连接语句创建的计数。

@shopping_setups = ShoppingSetup.joins(:company).
  joins("LEFT JOIN products on companies.id = products.company_id").
  joins("LEFT JOIN categories on companies.id = categories.company_id").
  select("shopping_setups.*").
  select("COUNT(products.company_id) AS products_count").
  select("COUNT(categories.company_id) AS categories_count").
  group("shopping_setups.id, companies.id, products.company_id, categories.company_id")

class ShoppingSetup
    belongs_to :company
end  

class Company
    has_one :shopping_setup
    has_many :products
    has_many :categories
end

class Product
    belongs_to :company
end

class Category
    belongs_to :company
end

编辑：问题是我做错了什么？为什么连接中的计数返回了这么多重复的行？