Find the Next available date which is not necessarily the Maximum Date

Question

Morning folks!
I am trying to find the next scheduled appointment date (Including any day after today) for a patient which may not be the maximum date for that person. I am trying to do this in Oracle Forms. My Query is working in SQL*Plus but is not working in Forms.
FUNCTION get_next_sched_date(P_PATIENT_ID in varchar2) RETURN DATE IS
  v_next_scheduled_date   patient_visit.target_date%TYPE;
BEGIN
  select next_target_date into v_next_scheduled_date
  from   ( select v.*, max(target_date) over (partition by patient_id) max_target_date,
                       lead(target_date) over (partition by patient_id order by target_date) next_target_date
           from   patient_visit v)
  where  patient_id = P_PATIENT_ID
  and    next_target_date >= SYSDATE
  and    max_target_date > next_target_date;
  return( v_next_scheduled_date );
EXCEPTION
   when NO_DATA_FOUND then
     return(NULL);
When I compile this in Oracle Forms, it gives me an Error.Encountered the symbol "(" when expecting one of the following: ,from.
I also noticed that Oracle Forms is not liking keywords such as LAG and LEAD. I am working on Oracle Forms 9i.
Any idea what I am doing wrong here? Thanks for listening to my Monday harping. :-)
Forms [32 Bit] Version 9.0.4.0.19 (Production)
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit ProductionEdited by: Roxyrollers on Aug 27, 2012 8:43 AM
Edited by: Roxyrollers on Aug 27, 2012 8:46 AM

Answer 1

Thanks.
For now, I have another simpler solution. I was just curious if the first way would have worked.
select MIN(target_date) into v_next_scheduled_date from patient_visit v1
where  patient_id = P_PATIENT_ID
and    target_date >= SYSDATE
and    target_date <= (select MAX(target_date) from patient_visit v2
                       where  v2.patient_id = v1.patient_id);Edited by: Roxyrollers on Aug 27, 2012 9:16 AM