Simplest ALV template

*&---------------------------------------------------------------------*
*& Report ZMMU100
*&---------------------------------------------------------------------*
*& System        :   Program name 
*& Module        :  MM
*& Program ID    :   ZMMU100
*& Author        :  john
*& Date          : 20210616
*& Description   :  Program Introduction 
*&---------------------------------------------------------------------*
*&  Modify the record    :
*&  Edition             date                  Modifier 
*& NO**         YYYY/MM/DD             XXX
*&---------------------------------------------------------------------*
*&---------------------------------------------------------------------*
REPORT zmmu100.
TABLES:zmmt021.

TYPE-POOLS:slis.
DATA:mail_ret   TYPE  zsappo_ret_info.
DATA:gt_fieldcat TYPE STANDARD TABLE OF lvc_s_fcat.
DATA:gs_fieldcat LIKE LINE OF gt_fieldcat.
DATA:gt_events TYPE  slis_t_event.
DATA:gt_repid TYPE sy-repid.
*DATA:GS_EVENTS LIKE LINE OF GT_EVENTS.
DATA:gs_layout TYPE  lvc_s_layo.
*DATA:GS_LAYOUT LIKE LINE OF GT_LAYOUT.

DATA:chat_input TYPE zmsg01.

DATA:BEGIN OF gt_data OCCURS 0,
       ebeln  TYPE zmmt021-ebeln,
       status TYPE zmmt021-status,
       zdate  TYPE zmmt021-zdate,
       ztime  TYPE zmmt021-ztime,
       ernam  TYPE ekko-ernam,
       msg    TYPE string,
     END OF gt_data.

DATA:t_tab    TYPE zmms005_t,
     is_req   TYPE  zsappo_req_info,
     is_input TYPE  zmms006,
     es_ret   TYPE  zsappo_ret_info,
     chat_RET TYPE zsappo_ret_info.


SELECTION-SCREEN BEGIN OF BLOCK col WITH FRAME TITLE TEXT-001.
  SELECT-OPTIONS: s_ebeln FOR zmmt021-ebeln .
  SELECT-OPTIONS: s_STATUS FOR zmmt021-status DEFAULT 'N'.
  SELECT-OPTIONS: s_ZDATE FOR zmmt021-zdate.
  SELECT-OPTIONS: s_ZTIME FOR zmmt021-ztime.
SELECTION-SCREEN END OF BLOCK col.

DEFINE fill_field.
  CLEAR gs_fieldcat.
  gs_fieldcat-fieldname = &1. "ALV  control :  Field name of internal table field 
  gs_fieldcat-scrtext_l = &2. " Long field label 
  gs_fieldcat-no_zero   = &3. "ALV  control :  Hide zero for output 
  gs_fieldcat-ref_table = &4. " Refer to table 
  gs_fieldcat-ref_field = &5. " Reference field 
  APPEND gs_fieldcat TO gt_fieldcat.
END-OF-DEFINITION.

START-OF-SELECTION. " The sequence in which the program occurs 
  PERFORM frm_get_data.  " Count 
  PERFORM frm_process_data. " Processing data 
  PERFORM frm_set_layout.  "LAYOUT Parameter setting 
  PERFORM frm_set_fieldcat. " Set up FIELDCAT Parameters 
  PERFORM frm_top_of_page.  "TOP_OF_PAGE  Parameter setting 

END-OF-SELECTION.
*&---------------------------------------------------------------------*
*& Form frm_get_data
*&---------------------------------------------------------------------*
*& text
*&---------------------------------------------------------------------*
*& -->  p1        text
*& <--  p2        text
*&---------------------------------------------------------------------*
FORM frm_get_data .
  DATA:lt_return LIKE TABLE OF bapireturn WITH HEADER LINE.
  CLEAR:lt_return[].
  DATA ls_zmmt021 TYPE zmmt021.

  SELECT DISTINCT a~ebeln,a~status,a~zdate,a~ztime,b~ernam
    INTO TABLE @DATA(lt_ebeln)
    FROM zmmt021 AS a
    INNER JOIN ekko AS b ON b~ebeln = a~ebeln
    AND b~frgke = 'Z'
    AND b~ihrez <> 'X'
   WHERE a~ebeln IN @s_ebeln
    AND  a~status IN @s_status
    AND  a~zdate IN @s_zdate
    AND  a~ztime IN @s_ztime.


  LOOP AT lt_ebeln ASSIGNING FIELD-SYMBOL(<fs>).
    MOVE-CORRESPONDING <fs> TO gt_data.  " Field auto match 
    MOVE-CORRESPONDING <fs> TO ls_zmmt021.  " Field auto match 
    APPEND gt_data.
  ENDLOOP.
ENDFORM.
*&---------------------------------------------------------------------*
*& Form frm_process_data
*&---------------------------------------------------------------------*
*& text
*&---------------------------------------------------------------------*
*& -->  p1        text
*& <--  p2        text
*&---------------------------------------------------------------------*
FORM frm_process_data .

ENDFORM.
*&---------------------------------------------------------------------*
*& Form frm_set_layout
*&---------------------------------------------------------------------*
*& text
*&---------------------------------------------------------------------*
*& -->  p1        text
*& <--  p2        text
*&---------------------------------------------------------------------*
FORM frm_set_layout .
  gs_layout-zebra         = 'X'.
  gs_layout-cwidth_opt    = 'X'.
  gs_layout-detailinit      = 'X'.
ENDFORM.
*&---------------------------------------------------------------------*
*& Form frm_set_fieldcat
*&---------------------------------------------------------------------*
*& text
*&---------------------------------------------------------------------*
*& -->  p1        text
*& <--  p2        text
*&---------------------------------------------------------------------*
FORM frm_set_fieldcat .
  REFRESH gt_fieldcat.
  fill_field:'EBELN' ' Purchase order '  'X' 'EKKO' 'EBELN',
             'STATUS' ' state '  'X' ''    '',
             'ZDATE' ' date '  'X' ''    '',
             'ZTIME' ' Time '  'X' ''    '',
             'ERNAM' ' Purchaser ' 'X' ''    '',
             'MSG' ' news '  'X' ''    ''.


  gt_repid  = sy-repid.
  SORT gt_data BY ebeln.
  CALL FUNCTION 'REUSE_ALV_GRID_DISPLAY_LVC'
    EXPORTING
      i_callback_program     = gt_repid
*     i_callback_user_command = 'USER_COMMAND' " Double-click the event 
      i_callback_top_of_page = 'FRM_TOP_OF_PAGE'  " Header 
      is_layout_lvc          = gs_layout
      it_fieldcat_lvc        = gt_fieldcat[]
      i_save                 = 'A'
      it_events              = gt_events
    TABLES
      t_outtab               = gt_data[]
    EXCEPTIONS
      program_error          = 1
      OTHERS                 = 2.
  IF sy-subrc <> 0.
* Implement suitable error handling here
  ENDIF.
ENDFORM.
*&---------------------------------------------------------------------*
*& Form frm_top_of_page
*&---------------------------------------------------------------------*
*& text
*&---------------------------------------------------------------------*
*& -->  p1        text
*& <--  p2        text
*&---------------------------------------------------------------------*
FORM frm_top_of_page .
  DATA:gt_header     TYPE slis_t_listheader,
       wa_header     TYPE slis_listheader,
       t_line        LIKE wa_header-info,
       ld_lines      TYPE i,
       ld_linesc(10) TYPE c.

  "TITLE  title 

  wa_header-typ  = 'H'. " The font of the title 
  wa_header-info = ' Manually push purchase orders to OA System records '.
  APPEND wa_header TO gt_header.
  CLEAR:wa_header.

  "DATE  Tabulated date 

  wa_header-typ = 'S'. " Font of tabulation date 
  wa_header-key = 'DATE:'. " Date title 
  CONCATENATE sy-datum(4)'.'
              sy-datum+4(2)'.'" From 4 Character truncation 2 position 
              sy-datum+6(2)
              INTO wa_header-info.  "TODAY DATE
  APPEND wa_header TO gt_header.
  CLEAR:wa_header.

  "TOTAL NO.OF RECORDS SELECTED
  DESCRIBE TABLE gt_data LINES ld_lines.
  ld_linesc = ld_lines.
  CONCATENATE 'TOTAL NO.OF RECORDS SELECTED:' ld_linesc "   Convert to text format 
              INTO t_line SEPARATED BY space.
  wa_header-typ  = 'A'.  "A In italics 
  wa_header-info = t_line.
  APPEND wa_header TO gt_header.
  CLEAR:wa_header,
        t_line.

  CALL FUNCTION 'REUSE_ALV_COMMENTARY_WRITE'   " Control the output of header data 
    EXPORTING
      it_list_commentary = gt_header.    " Header parameters 
ENDFORM.