In Line Items if any duplicate reocords found don't delete

Question

In Line Items if any duplicate reocords found don't delete   catch those records and display in output as Warning message.
PO      line item
123     1
123     2
123     3
123     1
134      1
in the above scenario there are 1 line item duplicate record . I want to catch that and display it as an Error / Warning message and    don't process that record continue to the next PO 134 like that.

Answer 1

The below code works considering the duplicates of both f1 and f2.
if you only require f1.then change the control break statements to f1.
DATA:BEGIN OF itab OCCURS 0,
      f1 TYPE char3,
      f2 TYPE char1,
    END OF itab.
DATA:wa LIKE LINE OF itab.
data:count type i.
wa-f1 = '123'. wa-f2 = '1'.APPEND wa TO itab.
wa-f1 = '123'. wa-f2 = '2'.APPEND wa TO itab.
wa-f1 = '123'. wa-f2 = '3'.APPEND wa TO itab.
wa-f1 = '123'. wa-f2 = '1'.APPEND wa TO itab.
wa-f1 = '134'. wa-f2 = '1'.APPEND wa TO itab.
SORT itab ASCENDING.
LOOP AT itab.
  AT NEW f2.
    count = 0.
  ENDAT.
  ADD 1 TO count.
  AT END OF f2.
    READ TABLE itab INTO wa INDEX sy-tabix.
    IF count = 2.
      write: 'E'.
      "move the error records.
    ELSE.
      Write:'S'.
      "Process the records
    ENDIF.
  ENDAT.
ENDLOOP.