class AddLastVersionAtToPosts < ActiveRecord::Migration[4.2] def change add_column :posts, :last_version_at, :timestamp execute "UPDATE posts SET last_version_at = COALESCE((SELECT max(created_at) FROM versions WHERE versions.versioned_id = posts.id AND versions.versioned_type = 'Post'), posts.created_at)" change_column :posts, :last_version_at, :timestamp, null: false end end