想要返回所有类别的产品，但只返回传递给查询的那些产品

Question

我的选择查询会返回一个不同的产品，以及产品所具有的类别列表。但是，它只返回传递给我的查询的^categories列表中的类别，即使它实际上有另外5个类别。我想返回所有产品类别，即使^categories列表中只有一个类别传入函数：

  def create_query_no_keyword(categories, shop_ids) do
    products_shops_categories = from p in Product,
    distinct: p.id,
    join: ps in ProductShop, on: p.id == ps.p_id,
    join: s in Shop, on: s.id == ps.s_id,
    join: pc in ProductCategory, on: p.id == pc.p_id,
    join: c in Subcategory, on: c.id == pc.c_id,
    where: c.id in ^categories,
    where: s.id in ^shop_ids,
    group_by: [p.id, p.name, p.brand],
    select: %{product: p, categories: fragment("json_agg( DISTINCT (?, ?)) AS category", c.id, c.name), shops: fragment("json_agg( DISTINCT (?, ?, ?)) AS shop", s.id, s.name, s.point)}
  end

如果只有一个类别传入上述函数，当产品实际上有8个类别时，为什么返回的产品只返回一个类别？

架构（product_categories实际使用Subcategory - 只是命名不同）：

 schema "products" do
    field :name, :string
    field :brand, :string
    field :description, :string
    field :image, :string
    field :rating, :integer
    field :number_of_votes, :integer
  end

  schema "subcategories" do
    field :name, :string
  end

  schema "product_categories" do
    field :c_id, :integer
    field :p_id, :integer
  end

  schema "shops" do
    field :name, :string
    field :place_id, :string
    field :point, Geo.Point
    field :geo_json, :string, virtual: true
    field :distance, :float, virtual: true

    timestamps()
  end

  schema "product_shops" do
    field :s_id, :integer
    field :p_id, :integer
  end