Here is an example with some comments.
First, Datadefinition
TYPE-POOLS slis. "import you need for REUSE_ALV_FIELDCATALOG_MERGE
DATA:
lt_fieldcat TYPE slis_t_fieldcat_alv,
BEGIN OF G_IT_MATERIAL occurs 0,
MATNR LIKE MARA-MATNR,
MTART LIKE MARA-MTART,
MAKTX_DE LIKE MAKT-MAKTX,
MAKTX_FR LIKE MAKT-MAKTX,
MAKTX_IT LIKE MAKT-MAKTX,
ERNAM LIKE MARA-ERNAM,
ERSDA LIKE MARA-ERSDA,
LAEDA LIKE MARA-LAEDA,
END OF G_IT_MATERIAL.
It is absolutley necesssairy that you define your local structur directly with LIKE, otherwise the parser from REUSE_ALV_FIELDCATALOG_MERGE will not find it.
select your stuff:
SELECT ma~matnr ma~mtart ma~ernam ma~ersda ma~laeda
de~maktx as maktx_de fr~maktx as maktx_fr it~maktx as maktx_it
FROM mara as ma
LEFT JOIN MAKT as de ON de~matnr = ma~matnr AND de~spras = 'DE'
LEFT JOIN MAKT as fr ON fr~matnr = ma~matnr AND fr~spras = 'FR'
LEFT JOIN MAKT as it ON it~matnr = ma~matnr AND it~spras = 'IT'
INTO CORRESPONDING FIELDS OF TABLE g_it_material
WHERE ...
create dynamicliy a field catalog
CALL FUNCTION 'REUSE_ALV_FIELDCATALOG_MERGE'
EXPORTING
I_PROGRAM_NAME = sy-repid
I_INTERNAL_TABNAME = 'G_IT_MATERIAL'
I_INCLNAME = sy-repid
CHANGING
ct_fieldcat = lt_fieldcat
EXCEPTIONS
inconsistent_interface = 1
program_error = 2
OTHERS = 3.
IF sy-subrc <> 0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
* WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
ENDIF.
now display that ALV grid
CALL FUNCTION 'REUSE_ALV_GRID_DISPLAY'
EXPORTING
it_fieldcat = lt_fieldcat "you could also give a structure
"i_structure_name = 'ZMM_SMATERIAL' "here instead of the fieldcat
TABLES
t_outtab = g_it_material
EXCEPTIONS
program_error = 1
OTHERS = 2.
Note that the parser also needs a max linesize of 72.