Help with selecting chuncks of data from a table

Question

Hi all,
I need help with a query that should do the following.
I have a table with vessel messages, and I need to get the last "NumMsgs" messages from a group of vessels.
The problem I have is that if I order the table by Vessel_ID, MessageDate DESC, I can´t do ROWNUM < NumMsgs (<-- Then number of messages to be shown is a user parameter)
I know it should be something like:
select * from (
select *
from Messages m
where TRIM(m.V_ID) = '11597' /* I was trying for a single vessel atm */
order by m.V_ID, m.MESSAGEDATE desc
where rownum < :NumMsgs
Any ideas?
Thanks in advance !

Answer 1

Hi,
What about :
select *
from (
select m.*, row_number() (order by m.V_ID, m.MESSAGEDATE desc) rn
from Messages m
where TRIM(m.V_ID) = '11597' /* I was trying for a single vessel atm */
where rn < :NumMsgsAnyway, I don't very well understand your problem, your query work fine, see for example :
SQL> ed
Wrote file afiedt.buf
  1  select object_name, object_id
  2  from
  3  (select object_name, object_id, row_number() over (order by object_id desc) as rn
  4   from dba_objects)
  5* where rn < 4
SQL> /
PS_TL_MTCHD_118     71763
PS_TL_MTCHD_117     71762
PS_TL_MTCHD_116     71761
SQL> ed
Wrote file afiedt.buf
  1  select object_name, object_id
  2  from
  3  (select object_name, object_id
  4   from dba_objects
  5   order by object_id desc)
  6* where rownum < 4
SQL> /
PS_TL_MTCHD_118     71763
PS_TL_MTCHD_117     71762
PS_TL_MTCHD_116     71761
SQL> Nicolas.
Message was edited by:
N. Gasparotto