If I only have order_count, net_gmv and gmv and then 1 month later I want to add avg_user_session, then what I understand is we need to backfill the `session_time` to the 'main' table and do the "avg(session_time) group by user_id" to the final table.

Or are you saying that we can just create another similar table with only avg_user_session and then join by the dimension key?