SELECT CUSTOMER, MAX(LAST_CALL_DUR), MAX(MAX_DUR)
FROM
(SELECT CUSTOMER,
       FIRST_VALUE (DURATION) OVER (PARTITION BY CUSTOMER ORDER BY CALL_DATE DESC) AS LAST_CALL_DUR,
       MAX(DURATION) OVER (PARTITION BY CUSTOMER) MAX_DUR
FROM PHONE_CALLS)
GROUP BY CUSTOMER;