redmine/db/migrate/066_add_custom_value_customized_index.rb

class AddCustomValueCustomizedIndex < ActiveRecord::Migration[4.2]
  def self.up
    add_index :custom_values, [:customized_type, :customized_id], :name => :custom_values_customized
  end

  def self.down
    remove_index :custom_values, :name => :custom_values_customized
  end
end