运行迁移时出现重复列名错误

I already have a "Add Photo to User" migration. Here it is:

class AddAttachmentPhotoToUsers < ActiveRecord::Migration
   def self.up
     change_table :users do |t|
     t.has_attached_file :photo
    end
   end

  def self.down
   drop_attached_file :users, :photo
  end
end

这是用户迁移:

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
    t.string :name
    t.string :title
    t.string :department
    t.text :skills
    t.boolean :available

    t.timestamps
   end
 end
end

我对此有点困惑，因为它告诉我有一个重复的列名photo_file_name"，但我需要将它添加到用户表中?那没有意义.我不需要删除它吗?