Oracle select most recent date record

Question

I am trying to find the most recent record based on a date field. When I set latest = 1 in the where clause, I get an error. Please help if possible. DATE is a the field I'm sorting by. I have tried both latest = 1 and latest = '1'

SELECT 
STAFF_ID,
SITE_ID,
PAY_LEVEL,
ROW_NUMBER() OVER (PARTITION BY STAFF_ID ORDER BY DATE DESC) latest

 FROM OWNER.TABLE
WHERE   END_ENROLLMENT_DATE is null 
AND latest = 1

Answer 1

you can't use aliases from select list inside the WHERE clause (because of the Order of Evaluation of a SELECT statement)

also you cannot use OVER clause inside WHERE clause - "You can specify analytic functions with this clause in the select list or ORDER BY clause." (citation from docs.oracle.com)

select *
from (select
  staff_id, site_id, pay_level, date, 
  max(date) over (partition by staff_id) max_date
  from owner.table
  where end_enrollment_date is null
)
where date = max_date

Answer 2

Assuming staff_id + date form a uk, this is another method:

SELECT STAFF_ID, SITE_ID, PAY_LEVEL
  FROM TABLE t
  WHERE END_ENROLLMENT_DATE is null
    AND DATE = (SELECT MAX(DATE)
                  FROM TABLE
                  WHERE staff_id = t.staff_id
                    AND DATE <= SYSDATE)