Run second sql statement only if first sql statement is null.

Question

Hey guys I seem to have a mental block here. I have two sql statements. I would like the second to run only if the first sql statement is null.I know i can potentially use PLsql but would really like to see if i can do this with straight up sql. Your responses are very very appreciated.
here is the first sql
  Select     ft.fund_code,
             ft.orgn_code,
             ft.acct_code,
             ft.amount,
             fb.owner_pidm,
             ft.prog_code     
      from ftrbremb fb , ftcractg ft
      where fb.doc_code = 'TR000038'
      and fb.ftpbport_id = ft.ftpbport_idsecond sql statement
     Select ft.fund_code,
             ft.orgn_code,
             ft.acct_code,
             ft.amount,
             fb.owner_pidm,
             ft.prog_code     
      from ftrbremb fb , ftcractg ft, ftprexps fx
      where fb.doc_code = 'TR000038'
      --and fb.ftpbport_id = ft.ftpbport_id
      and fx.ftrbremb_id = fb.id
      and ft.ftprexps_id = fx.id;How can i combine these two statements together so that when the first one is null the second one runs. As a bonus i like to get just the first row as well.
Any help would greatly appreciated. I tried to accomplish with case statement but it just dosent seem to be working for me.
Thanks

Answer 1

select ft.fund_code, ft.orgn_code, ft.acct_code, ft.amount, fb.owner_pidm, ft.prog_code
  from ftrbremb fb, ftcractg ft
where fb.doc_code = 'TR000038'
   and fb.ftpbport_id = ft.ftpbport_id
union all
select ft.fund_code, ft.orgn_code, ft.acct_code, ft.amount, fb.owner_pidm, ft.prog_code
  from ftrbremb fb, ftcractg ft, ftprexps fx
where fb.doc_code = 'TR000038'
   --and fb.ftpbport_id = ft.ftpbport_id
   and fx.ftrbremb_id = fb.id
   and ft.ftprexps_id = fx.id
   and not exists
         (select null
            from ftrbremb fb, ftcractg ft
           where fb.doc_code = 'TR000038'
             and fb.ftpbport_id = ft.ftpbport_id)