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我正在使用 merit gem 为我的应用程序添加信誉系统。我需要找到用户添加到帖子的点数。我想出的解决方案是将用户在进行投票操作时添加到帖子中的点数相加： 

SELECT SUM(num_points)
FROM merit_actions
INNER JOIN merit_activity_logs
ON merit_activity_logs.action_id = merit_actions.id
INNER JOIN merit_score_points
ON merit_score_points.id = merit_activity_logs.related_change_id
INNER JOIN merit_scores
ON merit_scores.id = merit_score_points.score_id
WHERE target_id = post.id
AND target_model = post.class.table_name
AND user_id = post.id
AND sash_id = post.sash_id

这些是与信誉系统相关的表格：

create_table "merit_actions", force: :cascade do |t|
    t.integer  "user_id"
    t.string   "action_method"
    t.integer  "action_value"
    t.boolean  "had_errors",    default: false
    t.string   "target_model"
    t.integer  "target_id"
    t.text     "target_data"
    t.boolean  "processed",     default: false
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "merit_activity_logs", force: :cascade do |t|
    t.integer  "action_id"
    t.string   "related_change_type"
    t.integer  "related_change_id"
    t.string   "description"
    t.datetime "created_at"
  end

  create_table "merit_score_points", force: :cascade do |t|
    t.integer  "score_id"
    t.integer  "num_points", default: 0
    t.string   "log"
    t.datetime "created_at"
  end

  create_table "merit_scores", force: :cascade do |t|
    t.integer "sash_id"
    t.string  "category", default: "default"
  end

从优点库复制的相关模型：

class Action < ActiveRecord::Base
    self.table_name = :merit_actions

    has_many :activity_logs, class_name: 'Merit::ActivityLog'
end

class ActivityLog < ActiveRecord::Base
    self.table_name = :merit_activity_logs

    belongs_to :action, class_name: 'Merit::Action'
    belongs_to :related_change, polymorphic: true
    has_one :sash, through: :related_change
end

class Sash < ActiveRecord::Base
    include Base::Sash
    has_many :scores, dependent: :destroy, class_name: 'Merit::Score'
end

class Score < ActiveRecord::Base
    self.table_name = :merit_scores
    belongs_to :sash
    has_many :score_points,
             dependent: :destroy,
             class_name: 'Merit::Score::Point'

    def points
      score_points.group(:score_id).sum(:num_points).values.first || 0
    end

    class Point < ActiveRecord::Base
      belongs_to :score, class_name: 'Merit::Score'
      has_one :sash, through: :score
      has_many :activity_logs,
               class_name: 'Merit::ActivityLog',
               as: :related_change
      delegate :sash_id, to: :score
    end
  end

为此，我该如何编写上述 SQL 查询？

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