You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 20140815183851_fix_index_on_post_actions.rb
    path of file: ./repos/discourse/db/migrate
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class FixIndexOnPostActions < ActiveRecord::Migration[4.2]
  def change
    execute "UPDATE post_actions SET targets_topic = false WHERE targets_topic IS NULL"
    change_column :post_actions, :targets_to
    
  def change
    execute "UPDATE post_actions SET targets_topic = false WHERE targets_topic IS NULL"
    change_column :post_actions, :targets_topic, :boolean, default: false, null: false

    execute "
    DELETE FROM post_actions pa
                    USING post_actions x
    WHERE pa.user_id = x.user_id AND
          pa.post_action_type_id = x.post_action_type_id AND
          pa.post_id = x.post_id AND
          pa.targets_topic = x.targets_topic AND
          pa.id < x.id AND
          pa.deleted_at IS NULL AND
          x.deleted_at IS NULL
    "

    remove_index "post_actions", name: "idx_unique_actions"
    add_index "post_actions",
              %w[user_id post_action_type_id post_id targets_topic],
              name: "idx_unique_actions",
              unique: true,
              where: "deleted_at IS NULL"
  end