What is the average number of orders purchased across all vendors? What is the average cost across all vendors?

basic_sql_explore_8.sql

select
avg(i.num_orders) as average_num_orders,
avg(i.subtotal) as average_subtotal
from (
  select
  y.name,
  count(distinct x.purchaseorderid) as num_orders,
  sum(x.subtotal) as subtotal
  from purchasing.purchaseorderheader x
  left join purchasing.vendor y
  on x.vendorid = y.businessentityid
  group by y.name
) i;