Help to rewrite left outer join

Question

I have the query below running on Db2 AND SQL SERVER 2005 with the syntax as shown. I cannot find a way to make Oracle work with this syntax.
Can you, please help me do this?
I need to keep all database statements the same for all databases and in this case I cannot implement this one.
Regular statement that I do not want to use anymore because executes additional filters:
SELECT
s.conflict_id as source_id,
s.disp_comments --some more fields going here
FROM sep_conflict s
left outer join app_activity_history h hist
on s.conflict_id = hist.source_idNew syntax for SQL server and db2 that I need analog for Oracle:
SELECT
s.conflict_id as source_id,
s.disp_comments --some more fields going here
FROM sep_conflict s
left outer join (select source_id from app_activity_history h )as hist (source_id)
on s.conflict_id = hist.source_idThanks a lot for the help, mj

Answer 1

Your second query looks similar to this;
SQL> with sep_conflict as (
   select 1 conflict_id, 1 disp_comments from dual union all
   select 2 conflict_id, 2 disp_comments from dual),
     app_activity_history as (
   select 1 source_id from dual union all
   select null source_id from dual)
/* End of test data */
SELECT
   s.conflict_id source_id, s.disp_comments, hist.source_id
FROM sep_conflict s
left outer join (select source_id
     from app_activity_history) hist
on s.conflict_id = hist.source_id
SOURCE_ID DISP_COMMENTS  SOURCE_ID
         1             1          1
         2             2          
2 rows selected.