Use of Extract datasets

Question

Hello,
Having seen various instances of the EXTRACT command in some legacy code I've got around to trying out this command but I can't get it to work properly. Here's some condensed test code I've put together:
TABLES: VBAK, VBAP.
FIELD-GROUPS: HEADER, TOP, DETAIL.
INSERT: VBAK-VBELN VBAP-POSNR INTO HEADER,
             VBAK-ERDAT VBAK-ERNAM VBAK-KUNNR INTO TOP,
             VBAP-MATNR VBAP-CHARG VBAP-NETWR VBAP-WAERK INTO DETAIL.
PARAMETERS P_VKORG TYPE VBAK-VKORG.
SELECT *
  FROM VBAK
  WHERE VKORG = P_VKORG.
  EXTRACT TOP.
  SELECT *
    FROM VBAP
    WHERE VBELN = VBAK-VBELN.
        EXTRACT DETAIL.
    ENDSELECT.
ENDSELECT.
CLEAR: VBAK, VBAP.
SORT.
LOOP.
  WRITE:/ VBAK-VBELN, VBAP-POSNR, VBAK-ERDAT, VBAK-ERNAM, VBAK-KUNNR, VBAP-MATNR.
ENDLOOP.
OK, forget about the nested selects and other bad stuff, but how come I get the following output, and how should it be corrected:
1360043260 000000 06.05.2008 CARTEM2 304393 <<< extraneous line that doesn't exist
1360043260 000010 06.05.2008 CARTEM2 304393 34123376
1360043260 000020 06.05.2008 CARTEM2 304393 50492316
1360043260 000030 06.05.2008 CARTEM2 304393 50406766
Use of extracts seems a bit wierd and there's not a lot out there to properly explain how to use them (apart from examples using a logical database).
Thanks,
Chris.

Answer 1

Hi,
When the first EXTRACT statement occurs in a program, the system creates the extract dataset and adds the first extract record to it. In each subsequent EXTRACT statement, the new extract record is added to the dataset.
So instead of extract, modify the above code in two ways:
1) Select-End Select, Comment out the extract statement and fetch in a work area if data is fetched in workarea append it to an internal table.
2) Use Select into table, where in you can fetch all the data into an internal table and then use it for processing.
For better performance, use the second method. Below is how you can change.
SELECT *
  FROM VBAK
  INTO TABLE LT_VBAK
  WHERE VKORG = P_VKORG.
  SELECT *
    FROM VBAP
INTO TABLE LT_VBAP
FOR ALL ENTRIES IN LT_VBAK   
WHERE VBELN = VBAK-VBELN.
LOOP AT LT_VBAP INTO LS_VBAP.
READ TABLE LT_VBAK WITH KEY VBELN = LS_VBAP-VBELN
IF SY-SUBRC EQ 0.
  WRITE:/ LS_VBAK-VBELN, LS_VBAP-POSNR, LS_VBAK-ERDAT, LS_VBAK-ERNAM, LS_VBAK-KUNNR, LS_VBAP-MATNR.
ENDIF.
ENDLOOP.
Hope this helps you
Regards
Shiva