Looping and moving correct lines from WTAB to ITAB

Question

I have made the following declaration for my 2 internal tables.
DATA: BEGIN OF ITAB OCCURS 0,
      EBELN LIKE EKKO-EBELN,  "Purchasing Document Number
      EBELP LIKE EKPO-EBELP,  "Item Number of Purchasing Document
      EINDT LIKE EKET-EINDT,  "Item delivery date
      BUDAT LIKE EKBE-BUDAT,  "Posting Date in the Document
      LFBNR LIKE EKBE-LFBNR,  "Document No. of a Reference Document
      BELNR LIKE EKBE-BELNR,  "Number of Material Document
      BWART LIKE EKBE-BWART,  "Movement Type
      ELIKZ LIKE EKBE-ELIKZ,  "Delivery Completed Indicator
      MENGE LIKE EKET-MENGE,  "Scheduled quantity
      END OF ITAB.
DATA: BEGIN OF WTAB OCCURS 0,
      EBELN LIKE EKBE-EBELN,  "Purchasing Document Number
      EBELP LIKE EKBE-EBELP,  "Item Number of Purchasing Document
      BUDAT LIKE EKBE-BUDAT,  "Posting Date in the Document
      LFBNR LIKE EKBE-LFBNR,  "Document No. of a Reference Document
      BELNR LIKE EKBE-BELNR,  "Number of Material Document
      BWART LIKE EKBE-BWART,  "Movement Type
      ELIKZ LIKE EKBE-ELIKZ,  "Delivery Completed Indicator
      MENGE LIKE EKBE-MENGE,  "Quantity (Delivered)
      END OF WTAB.
I did a SELECT statement for table ITAB to append the fields of EBELN, EBELP and EINDT. Then i did another SELECT statement for table WTAB (using FOR ALL ENTRIES OF ITAB) for fields EBELN, EBELP, BUDAT, BWART, LRBNR and BELNR. Later, i did a loop in WTAB to move fields BUDAT, LFBNR and BELNR into table ITAB that corresponds to the EBELN and EBELP of ITAB, which looks something like this:
LOOP AT WTAB.
MOVE WTAB-BUDAT TO ITAB-BUDAT.
MOVE WTAB-LFBNR TO ITAB-LFBNR.
MOVE WTAB-BELNR TO ITAB-BELNR.
MOVE WTAB-BWART TO ITAB-BWART.
MODIFY ITAB TRANSPORTING BUDAT LFBNR BELNR BWART
  WHERE EBELN = WTAB-EBELN AND
        EBELP = WTAB-EBELP.
ENDLOOP.
I now need to ensure that the right line from WTAB (assume that in table WTAB will contain several lines for a particular EBELN) is moved to table ITAB (corresponding to the same EBELN and EBELP) based on several conditions:
1. If the sum of all WTAB-MENGE (Ex: 5-2+3 = 5 or 5-2-1 = 2) of an EBELN is LE to ITAB-MENGE (Ex: 5), only the WTAB line containing the earliest BUDAT (provided BWART = '101' or '122') is selected and moved into ITAB.
2. If the sum of all WTAB-MENGE (Ex: 5-3-2 = 0 or NULL value from the beginning) of an EBELN is 0 or blank, no line is selected to move to ITAB.
I was able to do logic that fulfill the first condition but i am unable to solve condition 2, because no matter what i do, a date (BUDAT) from WTAB still gets selected and moved to ITAB, although by right, no lines from WTAB should have been selected.
I can post the logic i used to fulfill condition 1 if you guys need to have a look at it.
Anybody could give me some hints?
I really need this urgently, i have to transport by the end of the week.

Answer 1

Ignore the earlier code i wrote, copied an older version of the code i written. Here's the one i am using now:
LOOP AT WTAB.
  AT NEW MENGE.
*--> Change value of movement type 102 and 122 to negative
    IF WTAB-BWART = '102' OR WTAB-BWART = '122'.
      COMPUTE NEGATIVE_VALUE = WTAB-MENGE * -1.
      MOVE NEGATIVE_VALUE TO WTAB-V_MENGE.
    ELSE.
      MOVE WTAB-MENGE TO WTAB-V_MENGE.
    ENDIF.
      ADD WTAB-V_MENGE TO SUM_MENGE.
  ENDAT.
ENDLOOP.
However, there is a flaw in the codes above. Since i'm using AT NEW MENGE...ENDAT statement, what would happen if the next value in MENGE is the same as the previous one (although they are of the same EBELN)? It wouldn't be taken into account, am i right in this?
As you have seen, i declared an extra field within WTAB as V_MENGE TYPE I and another 2 more field:
DATA: SUM_MENGE TYPE I.
DATA: NEGATIVE_VALUE TYPE I.