ABAP Select data from SAP table MSG_LOW into internal table

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Below is a number of ABAP code snippets to demonstrate how to select data from SAP MSG_LOW table and store it within an internal table, including using the newer @DATA inline declaration methods. It also shows you various ways to process this data using ABAP work area, inline declaration or field symbols including executing all the relevant CONVERSION_EXIT routines specific to MSG_LOW. See here for more generic Select statement tips.

Sometimes data within SAP is stored within the database table in a different format to what it is displayed to the user. These input/output conversation FM routines are what translates the data between the two formats.

There is also a full declaration of the MSG_LOW table where each field has a char/string type for you to simply copy and paste. This allows you to use processing that is only available to these field types such as the CONCATENATE statement.

DATA: IT_MSG_LOW TYPE STANDARD TABLE OF MSG_LOW,
      WA_MSG_LOW TYPE MSG_LOW,
      GD_STR TYPE STRING.

DATA: lo_typedescr type REF TO cl_abap_typedescr.
DATA: lv_fieldname type fieldname.

FIELD-SYMBOLS: <FIELD> TYPE any.
FIELD-SYMBOLS: <MSG_LOW> TYPE MSG_LOW.

*Process all fields in table header/work area as string values
  PERFORM process_as_string_field_values CHANGING wa_MSG_LOW.

SELECT *
*restrict ABAP select to first 10 rows
 UP TO 10 ROWS      
  FROM MSG_LOW
  INTO TABLE IT_MSG_LOW.

*Select data and declare internal table using in-line method @DATA
*SELECT *
*  FROM MSG_LOW
*  INTO TABLE @DATA(IT_MSG_LOW2).
*--Further methods of using ABAP code to  select data from SAP database tables

*You can also declare the header/work area using the in-line DATA declaration method
READ TABLE IT_MSG_LOW INDEX 1 INTO DATA(WA_MSG_LOW2).


*Demonstrate how to loop at an internal table and update values using a FIELD-SYMBOL
LOOP AT IT_MSG_LOW ASSIGNING <MSG_LOW>.

*To update a field value using a field symbol simply change the value via the field symbol pointer
<MSG_LOW>-MANDT = 1.
<MSG_LOW>-MSGHDL = 1.
<MSG_LOW>-HIGH_LEVEL_REF = 1.
<MSG_LOW>-MSGID = 1.
<MSG_LOW>-MSGNO = 1.

ENDLOOP.

LOOP AT IT_MSG_LOW INTO WA_MSG_LOW.
*Write horizonal line to screen report.
  WRITE:/ sy-uline.

*Write selected data to screen/report before conversion.
  WRITE:/ sy-vline,   WA_MSG_LOW-MSGV1, sy-vline,
  WA_MSG_LOW-MSGV2, sy-vline,
  WA_MSG_LOW-MSGV3, sy-vline,
  WA_MSG_LOW-MSGV4, sy-vline,
ENDLOOP.
   
*Add any further fields from structure WA_MSG_LOW you want to display...

  WRITE:/ sy-uline.
* Aternatively use generic code to Write field values (and NAME) to screen report
  DO.
    ASSIGN COMPONENT sy-index OF STRUCTURE wa_MSG_LOW TO <field>.
    IF sy-subrc <> 0. EXIT. ENDIF.
    WRITE:/ 'Field Value', <field>, sy-vline.
    gd_str = <field> .
    lo_typedescr ?= CL_ABAP_DATADESCR=>DESCRIBE_BY_DATA( <field> ).
    lv_fieldname = lo_typedescr->GET_RELATIVE_NAME( ).
    WRITE:/ 'Field Name', lv_fieldname.
  ENDDO.

  
*Redo loop but convert all fields from internal to out value  
LOOP AT IT_MSG_LOW INTO WA_MSG_LOW.


*Write horizonal line to screen report.
  WRITE:/ sy-uline.

*Convert all fields to display/output versions using conversion routines
  PERFORM convert_all_field_values CHANGING wa_EKKO.
	 
ENDLOOP.

  
*&---------------------------------------------------------------------*
*& Form convert_all_field_values
*&---------------------------------------------------------------------*
FORM convert_all_field_values CHANGING p_EKKO LIKE wa_EKKO.
DATA: ld_input(1000) TYPE c, ld_output(1000) TYPE C.
ENDFORM. 

*&---------------------------------------------------------------------*
*& Form process_as_string_field_values
*&---------------------------------------------------------------------*
FORM process_as_string_field_values CHANGING p_EKKO LIKE wa_EKKO.

TYPES: BEGIN OF T_MSG_LOW_STR, 
MANDT TYPE STRING,
MSGHDL TYPE STRING,
HIGH_LEVEL_REF TYPE STRING,
MSGID TYPE STRING,
MSGNO TYPE STRING,
MSGV1 TYPE STRING,
MSGV2 TYPE STRING,
MSGV3 TYPE STRING,
MSGV4 TYPE STRING,END OF T_EKKO_STR.
DATA: WA_MSG_LOW_STR type T_EKKO_STR.

DATA: ld_text TYPE string.

LOOP AT IT_EKKO INTO WA_EKKO.
  MOVE-CORRESPONDING wa_EKKO TO WA_EKKO_STR.
  CONCATENATE: sy-vline
WA_MSG_LOW_STR-MANDT sy-vline 
WA_MSG_LOW_STR-MSGHDL sy-vline 
WA_MSG_LOW_STR-HIGH_LEVEL_REF sy-vline 
WA_MSG_LOW_STR-MSGID sy-vline 
WA_MSG_LOW_STR-MSGNO sy-vline 
WA_MSG_LOW_STR-MSGV1 sy-vline 
WA_MSG_LOW_STR-MSGV2 sy-vline 
WA_MSG_LOW_STR-MSGV3 sy-vline 
WA_MSG_LOW_STR-MSGV4 sy-vline      INTO ld_text SEPARATED BY SPACE.

*Add any further fields from structure WA_EKKO_STR you want to CONCATENATE...
ENDLOOP.
ENDFORM.