Please explain me the code

Question

RANGES : r_matnr FOR mara-matnr .
SELECT lifnr
         matnr
            INTO CORRESPONDING FIELDS OF TABLE t_data
    FROM zdata
   WHERE lifnr = p_lifnr.
  LOOP AT t_data .
    r_matnr-sign   = 'I' .
    r_matnr-option = 'EQ' .
    r_matnr-low    = t_data-matnr .
    APPEND r_matnr .
  ENDLOOP.
SELECT mblnr
         matnr
            menge
    INTO TABLE lt_menge
    FROM mseg
     FOR ALL ENTRIES IN lt_itab
   WHERE mblnr = lt_itab-mblnr
     AND matnr IN r_matnr

Answer 1

Hello madan,
RANGES : r_matnr FOR mara-matnr .
"""range is being declared for material number
SELECT lifnr                         "Account Number of Vendor or Creditor
              matnr                      "Material number
INTO CORRESPONDING FIELDS OF
             TABLE t_data          "respective fields of internal table
              FROM zdata           "Source table
  WHERE
            lifnr = p_lifnr."p_lifnr is used  as selection criterion
"From the naming convention P_lifnr looks like a parameter entered by user
"So all material numbers and A/C numbers for a particular account number are being selected
"The following process is defining a range.r_matnr will contain all Material numbers
which are available for the account number P_lifnr
eg:imagine that you have 1,2,3  matnr having LIFNR '001' from ZDATA
then:::::after this loop r_matnr eill contain 1,2,3>
LOOP AT t_data .
r_matnr-sign = 'I' .
r_matnr-option = 'EQ' .
r_matnr-low = t_data-matnr .
APPEND r_matnr .
ENDLOOP.
"select X from Y where matnr IN r_matnr" means
it will select field X from table Y
where material number = '1' or '2' or '3'...(based on matrn in the t_data)
you are selecting from MSEG some fields which have material numbers in ZDATA for a particular
account number and which have mblnr values in lt_itab...ie records which have mblnr from lt_itab
and material number from ZDATA for the account number from the database table  mseg
SELECT mblnr
matnr
menge
INTO TABLE lt_menge
FROM mseg
FOR ALL ENTRIES IN lt_itab
WHERE mblnr = lt_itab-mblnr
AND matnr IN r_matnr
Reward if useful
Regards
Byju