用了宏，规则可以自己定义

METHOD set_plnal.

DATA:lv_plnal TYPE plnal.
DATA:lv_num2 TYPE num2.
DATA:lt_char1 TYPE TABLE OF char1.
DATA:lv_char1 TYPE char1.
DATA:lv_index TYPE i.
DATA:lv_f_c TYPE char1.
DATA:lv_s_c TYPE char1.

DEFINE add_c.
append &1 to lt_char1.
END-OF-DEFINITION.

add_c:‘0’,‘1’,‘2’,‘3’,‘4’,‘5’,‘6’,‘7’,‘8’,‘9’,‘A’,‘B’,‘C’,‘D’,‘E’,‘F’,‘G’,‘H’,‘I’,‘J’,‘K’,‘L’,‘M’,‘N’,‘O’,‘P’,‘Q’,‘R’,
‘S’,‘T’,‘U’,‘V’,‘W’,‘X’,‘Y’,‘Z’.

• SELECT SINGLE MAX( plnal ) INTO ev_plnal FROM plas WHERE plnnr = iv_plnnr.

  SELECT SINGLE MAX( plnal ) INTO ev_plnal FROM plko WHERE plnnr = iv_plnnr.

  IF sy-subrc <> 0.
  RETURN.
  ENDIF.

  IF ev_plnal CO ‘0123456789’.

  IF ev_plnal = ‘99’.

•  ev_plnal = 'A' && '0'.
  ev_plnal = 'A0'.
  

  ELSE.

  lv_num2 = ev_plnal.
  
  ev_plnal = lv_num2 + 1.
  

  ENDIF.

  ELSE.

  lv_s_c = ev_plnal+1(1).
  lv_f_c = ev_plnal+0(1).

  READ TABLE lt_char1 TRANSPORTING NO FIELDS WITH KEY table_line = lv_s_c BINARY SEARCH.

  IF sy-tabix = ‘36’.

  READ TABLE lt_char1 TRANSPORTING NO FIELDS WITH  KEY table_line = lv_f_c BINARY SEARCH.
  
  lv_index = sy-tabix + 1.
  
  READ TABLE lt_char1 INTO lv_char1 INDEX lv_index.
  
  ev_plnal+0(1) = lv_char1.
  
  IF lv_char1 CO  '0123456789'.
    ev_plnal+1(1) = 'A'.
  ELSE.
    ev_plnal+1(1) = '0'.
  ENDIF.
  

  ELSE.
  lv_index = sy-tabix + 1.

  READ TABLE lt_char1 INTO lv_char1 INDEX lv_index.
  
  ev_plnal+1(1) = lv_char1.
  

  ENDIF.

  ENDIF.

ENDMETHOD.