Help using collect statement

TABLES: EKKO, LFA1, EKPO.

TYPES: BEGIN OF ST_HEADER,

EBELN LIKE EKKO-EBELN,

LIFNR LIKE LFA1-LIFNR,

NAME1 LIKE LFA1-NAME1,

AEDAT LIKE EKKO-AEDAT,

ERNAM LIKE EKKO-ERNAM,

END OF ST_HEADER,

BEGIN OF ST_DETAIL,

EBELN LIKE EKKO-EBELN,

EBELP LIKE EKPO-EBELP,

TXZ01 LIKE EKPO-TXZ01,

NETWR LIKE EKPO-NETWR,

END OF ST_DETAIL.

DATA: WA_HEADER1 TYPE TABLE OF ST_HEADER,

WA_HEADER2 TYPE TABLE OF ST_HEADER,

WA_HEADERT TYPE TABLE OF ST_HEADER,

WA_DETAIL1 TYPE TABLE OF ST_DETAIL,

WA_DETAIL2 TYPE TABLE OF ST_DETAIL,

WA_DETAILT TYPE TABLE OF ST_DETAIL WITH HEADER LINE.

FIELD-SYMBOLS: <HD1> TYPE ST_HEADER,

<HD2> TYPE ST_HEADER,

<HD3> TYPE ST_HEADER,

<DT1> TYPE ST_DETAIL,

<DT2> TYPE ST_DETAIL,

<DT3> TYPE ST_DETAIL.

SELECT-OPTIONS: S_EBELN FOR EKKO-EBELN.

SELECT-OPTIONS: S_LIFNR FOR LFA1-LIFNR.

SELECT *

FROM EKKO

INTO CORRESPONDING FIELDS OF TABLE WA_HEADER1.

SELECT *

FROM LFA1

INTO CORRESPONDING FIELDS OF TABLE WA_HEADER2.

LOOP AT WA_HEADER1 ASSIGNING <HD1>.

LOOP AT WA_HEADER2 ASSIGNING <HD2>.

IF <HD1>-LIFNR EQ <HD2>-LIFNR.

APPEND INITIAL LINE TO WA_HEADERT ASSIGNING <HD3>.

<HD3>-EBELN = <HD1>-EBELN.

<HD3>-LIFNR = <HD2>-LIFNR.

<HD3>-NAME1 = <HD2>-NAME1.

<HD3>-AEDAT = <HD1>-AEDAT.

<HD3>-ERNAM = <HD1>-ERNAM.

ENDIF.

ENDLOOP.

ENDLOOP.

SELECT *

FROM EKKO

INTO CORRESPONDING FIELDS OF TABLE WA_DETAIL1.

SELECT *

FROM EKPO

INTO CORRESPONDING FIELDS OF TABLE WA_DETAIL2.

LOOP AT WA_DETAIL1 ASSIGNING <DT1>.

LOOP AT WA_DETAIL2 ASSIGNING <DT2>.

IF <DT1>-EBELN EQ <DT2>-EBELN.

APPEND INITIAL LINE TO WA_DETAILT ASSIGNING <DT3>.

<DT3>-EBELN = <DT1>-EBELN.

<DT3>-EBELP = <DT2>-EBELP.

<DT3>-TXZ01 = <DT2>-TXZ01.

<DT3>-NETWR = <DT2>-NETWR.

ENDIF.

ENDLOOP.

ENDLOOP.

LOOP AT WA_HEADERT ASSIGNING <HD1>.

WRITE: / <HD1>-EBELN COLOR COL_KEY,

<HD1>-LIFNR COLOR COL_GROUP,

<HD1>-NAME1 COLOR COL_GROUP,

<HD1>-AEDAT COLOR COL_GROUP,

<HD1>-ERNAM COLOR COL_GROUP.

AT END OF EBELN.

LOOP AT WA_DETAILT ASSIGNING <DT1>.

IF <HD1>-EBELN = <DT1>-EBELN.

WRITE: / ' ',

<DT1>-EBELP,

<DT1>-TXZ01,

<DT1>-NETWR.

ENDIF.

ENDLOOP.

ENDAT.

ENDLOOP.

Help!!

I need to get the sum of netwr of <dt1>-netwr but I couldn't use SUM as it forbids me when I'm using loop...assigning....I'm not so familiar with using Collect statement to get the sum of netwr.

the output is I got a header data then details..after all the details of a particular header comes the total.

regards,

Lawrence