DBMaster_ZD_T6_2

SELECT h.salesorderheaderid, h.customerid, h.orderdate
  , TRUNC(MAX(h.orderdate) over (PARTITION BY h.customerid) - h.orderdate) AS days_to_lastorder1
  , TRUNC(FIRST_VALUE(h.orderdate) over (PARTITION BY h.customerid ORDER BY h.orderdate DESC) - h.orderdate) AS days_to_lastorder2
  FROM dbmaster.salesorderheader h