Use below steps to calculate totals in ABAP ALV.

1. Build field catalog and set the field DO_SUM of field catalog to ‘X’ for the field for which you want calculate the totals.
2. Pass field catalog to function module ‘REUSE_ALV_GRID_DISPLAY’.

TYPE-POOLS: slis.  " SLIS contains all the ALV data types

*&---------------------------------------------------------------------*
*& Data Declaration
*&---------------------------------------------------------------------*
DATA: it_sbook     TYPE TABLE OF sbook.
DATA: it_fieldcat  TYPE slis_t_fieldcat_alv,
      wa_fieldcat  TYPE slis_fieldcat_alv.
*&---------------------------------------------------------------------*
*& START-OF-SELECTION
*&---------------------------------------------------------------------*
START-OF-SELECTION.

*Fetch data from the database
  SELECT * FROM sbook INTO TABLE it_sbook.

*Build field catalog
  wa_fieldcat-fieldname  = 'CARRID'.    " Fieldname in the data table
  wa_fieldcat-seltext_m  = 'Airline'.   " Column description in the output
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'CONNID'.
  wa_fieldcat-seltext_m  = 'Con. No.'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'FLDATE'.
  wa_fieldcat-seltext_m  = 'Date'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'BOOKID'.
  wa_fieldcat-seltext_m  = 'Book. ID'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'PASSNAME'.
  wa_fieldcat-seltext_m  = 'Passenger Name'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'LOCCURAM'.
  wa_fieldcat-seltext_m  = 'Price'.
*Calculate Total for Price  
  wa_fieldcat-do_sum     = 'X'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'LOCCURKEY'.
  wa_fieldcat-seltext_m  = 'Currency'.
  APPEND wa_fieldcat TO it_fieldcat.

*Pass data and field catalog to ALV function module to display ALV list
  CALL FUNCTION 'REUSE_ALV_GRID_DISPLAY'
    EXPORTING
      it_fieldcat   = it_fieldcat
    TABLES
      t_outtab      = it_sbook
    EXCEPTIONS
      program_error = 1
      OTHERS        = 2.

Output

Subtotal in ABAP ALV

To calculate subtotal in ALV, build sort catalog and set the field SUBTOT of sort catalog to ‘X’.

TYPE-POOLS: slis.  " SLIS contains all the ALV data types

*&---------------------------------------------------------------------*
*& Data Declaration
*&---------------------------------------------------------------------*
DATA: it_sbook     TYPE TABLE OF sbook.
DATA: it_fieldcat  TYPE slis_t_fieldcat_alv,
      wa_fieldcat  TYPE slis_fieldcat_alv,
      it_sort      TYPE slis_t_sortinfo_alv,
      wa_sort      TYPE slis_sortinfo_alv..
*&---------------------------------------------------------------------*
*& START-OF-SELECTION
*&---------------------------------------------------------------------*
START-OF-SELECTION.

*Fetch data from the database
  SELECT * FROM sbook INTO TABLE it_sbook.

*Build field catalog
  wa_fieldcat-fieldname  = 'CARRID'.    " Fieldname in the data table
  wa_fieldcat-seltext_m  = 'Airline'.   " Column description in the output
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'CONNID'.
  wa_fieldcat-seltext_m  = 'Con. No.'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'FLDATE'.
  wa_fieldcat-seltext_m  = 'Date'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'BOOKID'.
  wa_fieldcat-seltext_m  = 'Book. ID'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'PASSNAME'.
  wa_fieldcat-seltext_m  = 'Passenger Name'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'LOCCURAM'.
  wa_fieldcat-seltext_m  = 'Price'.
  wa_fieldcat-do_sum     = 'X'.
  APPEND wa_fieldcat TO it_fieldcat.

  wa_fieldcat-fieldname  = 'LOCCURKEY'.
  wa_fieldcat-seltext_m  = 'Currency'.
  APPEND wa_fieldcat TO it_fieldcat.
*Build sort catalog
  wa_sort-spos      = 1.
  wa_sort-fieldname = 'CARRID'.
  wa_sort-up        = 'X'.
  wa_sort-subtot    = 'X'.
  APPEND wa_sort TO it_sort.

*Pass data and field catalog to ALV function module to display ALV list
  CALL FUNCTION 'REUSE_ALV_GRID_DISPLAY'
    EXPORTING
      it_fieldcat   = it_fieldcat
      it_sort       = it_sort
    TABLES
      t_outtab      = it_sbook
    EXCEPTIONS
      program_error = 1
      OTHERS        = 2.

Output

If you want to calculate subtotals for more fields, just add a record in sort field catalog for each field.

*Build sort catalog
  wa_sort-spos      = 1.
  wa_sort-fieldname = 'CARRID'.
  wa_sort-up        = 'X'.
  wa_sort-subtot    = 'X'.
  APPEND wa_sort TO it_sort.

  wa_sort-spos      = 2.
  wa_sort-fieldname = 'CONNID'.
  wa_sort-up        = 'X'.
  wa_sort-subtot    = 'X'.
  APPEND wa_sort TO it_sort.

Output