Query help - max value

Question

Hello together,
I have the following example table:
PERSONID_____BEGINDATE_____ENDDATE_____ROOMID
1033_________1.10.2009______5.10.2009_____567
1033_________1.10.2010______5.10.2010_____891
1041_________2.11.2009______1.12.2009_____123
1041_________3.12.2010______3.12.2011_____456
What I need is the line with the highest end date by PERSONID.
In the example above I would need to see the 2nd and the 4th line.
This is the query I am using:
select example.personid, max(example.begindate), max(example.enddate), example.roomid
from example
where (example.enddate >= trunc(sysdate))
group by example.personid, example.roomid
The problem is it always gives me 4 result lines (in this example). I think because it gets grouped by the roomid, which is distinct in each line, in the example.
What I actually want is ONE result line, per person, which shows me the highest end date, independently of the room id.
Can someone please point me in the right direction? Using max(date) is correct?
Thank you very much in advance.

Answer 1

Hi,
Welcome to the forum!
The most versatile way is:
WITH     got_r_num     AS
     SELECT     e.*
     ,     ROW_NUMBER () OVER ( PARTITION BY  personid
                               ORDER BY          enddate     DESC
                       ) AS r_num
     FROM    example      e
     WHERE     enddate      >= TRUNC (SYSDATE)
SELECT  *     -- Or list all columns except r_num
FROM     got_r_num
WHERE     r_num     = 1
;What do you want to do in case of a tie? For example, what if both rows for personid=1033 had the same enddate?
The query above would pick one of them arbitarily.
If you want both of them, then change ROW_NUMBER to RANK.
If you want to add a tie-breaker (e.g., pick the one with the latest begindate), then add more columns to the analytic ORDER BY clause.
Edited by: Frank Kulash on Sep 15, 2009 2:12 PM
Added <tt>WHERE     enddate     >= TRUNC (SYSDATE)</tt> condition