Can you check for data in one table or another but not both in one query?

Question

I have a situation where I need to link two tables together but the data may be in another (archive) table or different records are in both but I want the latest record from either table:
ACCOUNT
AccountID     Name   
123               John Doe
124               Jane Donaldson           
125               Harold Douglas    
MARKETER_ACCOUNT
Key     AccountID     Marketer    StartDate     EndDate
1001     123               10526          8/3/2008     9/27/2009
1017     123               10987          9/28/2009     12/31/4712    (high date ~ which means currently with this marketer)
1023     124               10541          12/03/2010     12/31/4712
ARCHIVE
Key     AccountID     Marketer    StartDate     EndDate
1015     124               10526          8/3/2008     12/02/2010
1033     125               10987         01/01/2011     01/31/2012  
So my query needs to return the following:
123     John Doe                        10526     8/3/2008     9/27/2009
124     Jane Donaldson             10541     12/03/2010     12/31/4712     (this is the later of the two records for this account between archive and marketer_account tables)
125     Harold Douglas               10987          01/01/2011     01/31/2012     (he is only in archive, so get this record)
I'm unsure how to proceed in one query.  Note that I am reading in possibly multiple accounts at a time and returning a collection back to .net
open CURSOR_ACCT
          select AccountID
          from
                 ACCOUNT A,
                 MARKETER_ACCOUNT M,
                 ARCHIVE R
           where A.AccountID = nvl((select max(M.EndDate) from Marketer_account M2
                                                where M2.AccountID = A.AccountID),
                                                  (select max(R.EndDate) from Archive R2
                                                where R2.AccountID = A.AccountID)
               and upper(A.Name) like parameter || '%'
<can you do a NVL like this?   probably not...   I want to be able to get the MAX record for that account off the MarketerACcount table OR the max record for that account off the Archive table, but not both>
(parameter could be "DO", so I return all names starting with DO...)

Answer 1

if I understand your description I would assume that for John Dow we would expect the second row from marketer_account  ("high date ~ which means currently with this marketer"). Here is a solution with analytic functions:
drop table account;
drop table marketer_account;
drop table marketer_account_archive;
create table account (
    id number
  , name varchar2(20)
insert into account values (123, 'John Doe');
insert into account values (124, 'Jane Donaldson');
insert into account values (125, 'Harold Douglas');
create table marketer_account (
    key number
  , AccountId number
  , MktKey number
  , FromDt date
  , ToDate date
insert into marketer_account values (1001, 123, 10526, to_date('03.08.2008', 'dd.mm.yyyy'), to_date('27.09.2009', 'dd.mm.yyyy'));
insert into marketer_account values (1017, 123, 10987, to_date('28.09.2009', 'dd.mm.yyyy'), to_date('31.12.4712', 'dd.mm.yyyy'));
insert into marketer_account values (1023, 124, 10541, to_date('03.12.2010', 'dd.mm.yyyy'), to_date('31.12.4712', 'dd.mm.yyyy'));
create table marketer_account_archive (
    key number
  , AccountId number
  , MktKey number
  , FromDt date
  , ToDate date
insert into marketer_account_archive values (1015, 124, 10526, to_date('03.08.2008', 'dd.mm.yyyy'), to_date('02.12.2010', 'dd.mm.yyyy'));
insert into marketer_account_archive values (1033, 125, 10987, to_date('01.01.2011', 'dd.mm.yyyy'), to_date('31.01.2012', 'dd.mm.yyyy'));
select key, AccountId, MktKey, FromDt, ToDate
     , max(FromDt) over(partition by AccountId) max_FromDt
  from marketer_account
union all
select key, AccountId, MktKey, FromDt, ToDate
     , max(FromDt) over(partition by AccountId) max_FromDt
  from marketer_account_archive;
with
basedata as (
select key, AccountId, MktKey, FromDt, ToDate
  from marketer_account
union all
select key, AccountId, MktKey, FromDt, ToDate
  from marketer_account_archive
basedata_with_max_intervals as (
select key, AccountId, MktKey, FromDt, ToDate
     , row_number() over(partition by AccountId order by FromDt desc) FromDt_Rank
  from basedata
filtered_basedata as (
select key, AccountId, MktKey, FromDt, ToDate from basedata_with_max_intervals where FromDt_Rank = 1
select a.id
     , a.name
     , b.MktKey
     , b.FromDt
     , b.ToDate
  from account a
  join filtered_basedata b
    on (a.id = b.AccountId)
ID NAME                     MKTKEY FROMDT     TODATE
123 John Doe                  10987 28.09.2009 31.12.4712
124 Jane Donaldson            10541 03.12.2010 31.12.4712
125 Harold Douglas            10987 01.01.2011 31.01.2012
If your tables are big it could be necessary to do the filtering (according to your condition) in an early step (the first CTE).
Regards
Martin