Add index favourites on account_id and id (#4360)

db/migrate/20170720000000_add_index_favourites_on_account_id_and_id.rb

+class AddIndexFavouritesOnAccountIdAndId < ActiveRecord::Migration[5.1]
+  def change
+    # Used to query favourites of an account ordered by id.
+    add_index :favourites, [:account_id, :id]
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170718211102) do
+ActiveRecord::Schema.define(version: 20170720000000) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -103,6 +103,7 @@ ActiveRecord::Schema.define(version: 20170718211102) do
     t.integer "status_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["account_id", "id"], name: "index_favourites_on_account_id_and_id"
     t.index ["account_id", "status_id"], name: "index_favourites_on_account_id_and_status_id", unique: true
     t.index ["status_id"], name: "index_favourites_on_status_id"
   end