Indexes for derived tables

Hi,

I’m using a derived table for computing some details about a user. The Lookerml manual says that I can use indexes for derived tables, yet I get a warning about indexes being an unknown parameter for a derived table,

http://www.looker.com/docs/reference/derived-tables We use Redshift which I believe should be a Postgres dialect version.

Thank you.

- view: user_avg_value

  derived_table:

    sql: |

      SELECT  orders.user_id as user_id

              , orders.email as email

              , orders.website as website

              , AVG(orders.order_value) AS avg_value 

              , SUM(orders.order_value) AS total_value

              , SUM(orders.order_refund) AS total_refund

      FROM orders

      WHERE NOT cancelled GROUP BY orders.user_id, orders.website, orders.email



    indexes: [email, website]

    sortkeys: [email]

    persist_for: 24 hours