discourse/db/migrate/20130613211700_drop_posts_uploads.rb

class DropPostsUploads < ActiveRecord::Migration
  def up
    drop_table :posts_uploads
  end

  def down
    create_table :posts_uploads, id: false do |t|
      t.integer :post_id
      t.integer :upload_id
    end

    add_index :posts_uploads, :post_id
    add_index :posts_uploads, :upload_id
    add_index :posts_uploads, [:post_id, :upload_id], unique: true
  end
end