Internal table declaration - various ABAP code to implement an internal table

Declaring internal tables is an essential part of writing ABAP code as this is where most of the data retrieved from database tables will be stored. During the selectstatement you retrieve data from a database table into an internal table (multiple rows) or a work area or header line (single row).

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*& Report  ZTYPES                                              *
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REPORT  ZTYPES .

* Table declaration (old method)
DATA: BEGIN OF tab_ekpo OCCURS 0,             "itab with header line
  ebeln TYPE ekpo-ebeln,
  ebelp TYPE ekpo-ebelp,
 END OF tab_ekpo.

*Table declaration (new method)     "USE THIS WAY!!!
TYPES: BEGIN OF t_ekpo,
  ebeln TYPE ekpo-ebeln,
  ebelp TYPE ekpo-ebelp,
 END OF t_ekpo.
DATA: it_ekpo TYPE STANDARD TABLE OF t_ekpo INITIAL SIZE 0,      "itab
      wa_ekpo TYPE t_ekpo.                    "work area (header line)

* Build internal table and work area from existing internal table
DATA: it_datatab LIKE tab_ekpo OCCURS 0,      "old method
      wa_datatab LIKE LINE OF tab_ekpo.

* Build internal table and work area from existing internal table,
* adding additional fields
TYPES: BEGIN OF t_repdata.
        INCLUDE STRUCTURE tab_ekpo.  "could include EKKO table itself!!
TYPES: bukrs  TYPE ekpo-werks,
       bstyp  TYPE ekpo-bukrs.
TYPES: END OF t_repdata.
DATA: it_repdata TYPE STANDARD TABLE OF t_repdata INITIAL SIZE 0,   "itab
      wa_repdata TYPE t_repdata.                 "work area (header line)