Select 
 DPO.logical_business_unit ,
 DPO.po_number,
 SWS.upc,
 GPR.prim_size_desc,
 GSS.sec_size_desc,
 DPO.accepted_launch_order_qty,
 SWS.last_full_selling_price
from 
cms_db_purchase_order DPO,
cms_season_ways SWS,
cms_grd_primary_sizes GPR,
cms_grd_secondary_sizes GSS,
cms_db_intl_hubs DIH,
cms_db_purchase_order_hist poh ,
 ( select    max(poh.po_version_num)  as  max_po_version_num 
   from      cms_db_purchase_order_hist poh, 
             cms_db_purchase_order dpo 
   where     dpo.po_number=poh.po_number 
   and       poh.po_status='A'
   group by  poh.po_number having count(*)>1) sq
where DPO.year              = SWS.year
and  DPO.season_type        = SWS.season_type
and  DPO.Dept_num           = SWS.dept_num
and  DPO.stroke_num         = SWS.stroke_num
and  DPO.colour_code        = SWS.colour_code
and  SWS.prim_size_index    = GPR.prim_size_index
and  SWS.sec_size_index     = GSS.sec_size_index
and  intl_hub_flag          = 'Y’ 
and  DIH.hub_code           = DPO.final_warehouse_code
and  (DPO.po_status         = 'A' or 
      DPO.has_been_accepted = 'Y')
and  DPO.po_status         != 'C'
and  dpo.po_number          = poh.po_number
and  DPO.Version_num        in (sq.max_po_version_num)
and  DPO.Number_launch_packs= 0
and  DPO.Accepted_launch_order_qty is NULL

SQL> WITH TEST_TAB AS
  2  (SELECT 'A' Col_1, 1 Col_2 FROM Dual
  3  UNION ALL
  4  SELECT 'B' , 2 FROM Dual
  5  UNION ALL
  6  SELECT 'C', 3 FROM Dual
  7  UNION ALL
  8  SELECT 'D', 3 FROM Dual
  9  )
 10  SELECT * from TEST_TAB;

C      COL_2
- ----------
A          1
B          2
C          3
D          3

SQL> ed
Wrote file afiedt.buf

  1  WITH TEST_TAB AS
  2  (SELECT 'A' col_1, 1 col_2 FROM Dual
  3  UNION ALL
  4  SELECT 'B' , 2 FROM Dual
  5  UNION ALL
  6  SELECT 'C', 3 FROM Dual
  7  UNION ALL
  8  SELECT 'D', 3 FROM Dual
  9  )
 10  SELECT * from TEST_TAB
 11* WHERE col_2 = (SELECT MAX(col_2) FROM TEST_TAB)
 12  ;

C      COL_2
- ----------
C          3
D          3