moebooru/db/migrate/069_clean_up_users.rb

class CleanUpUsers < ActiveRecord::Migration[5.1]
  def self.up
    remove_column :users, :ip_addr
    remove_column :users, :tag_blacklist
    remove_column :users, :login_count
  end

  def self.down
    execute "ALTER TABLE users ADD COLUMN ip_addr inet NOT NULL"
    add_column :users, :tag_blacklist, :text, null: false, default: ""
    add_column :users, :login_count, :integer, null: false, default: 0
  end
end