MySQL 去重

activerecord_utils.rb

# -*- encoding: utf-8 -*-

class ActiveRecord::Base
  class << self
      # 去重
    def divorce_by(field_name, id = :id)
      ids = twin_ids_by(field_name, id)
      self.where(id: ids).delete_all unless ids.empty?
    end
    # 找出重复的 ids
    def twin_ids_by(field_name, id = :id)
      self.select(id).twins_by(field_name).uniq.pluck(id)
    end
    # 找出重复记录
    def twins_by(field_name, limit = 1)
      group(field_name).having('COUNT(?) > ?', field_name, limit)
    end
    # 反选字段
    def unselect(*args)
      self.select(self.column_names - args.map(&:to_s))
    end
  end
end

# 列出所有表名
module Kernel
  def tables
    ActiveRecord::Base.connection.tables
  end
end

ids = User.select(:id).group(field_name).having("count(#{field_name}) > 1").pluck(:id)
User.where(id: ids).delete_all unless ids.empty?

感谢 @yangxing-star 效率高很多。