ABOUT SELECT STATEMENT

My friends i have one question i tried it out but i am not getting the required output

Q ) I WANT TO KNOW IN THIS YEAR 2008 WHAT IS THE LARGEST SELLING ITEM IN MY COMPANY

I TRIED IT OUT LIKE THIS

BUT INSTEAD OF SUMMING UP ALL THE KBMENG VALUES I AM GETTING NILL VALUES HOW TO MAKE IT

PLEASE FIND ME THE SOLUTION. SO THAT I CAN PROCEED FURTHER

TABLES : vbak,

vbap.

DATA : BEGIN OF st,

matnr LIKE vbap-matnr, "Material Number

kbmeng LIKE vbap-kbmeng, "Cumulative confirmed Quantity in sales unit

END OF st.

DATA it LIKE st OCCURS 0 WITH HEADER LINE. "Internal table 1 decleration

SELECT-OPTIONS my_erdat FOR vbak-erdat. "date field

INITIALIZATION.

START-OF-SELECTION.

SELECT a_{matnr SUM( a}klmeng )

INTO CORRESPONDING FIELDS OF it

FROM vbap AS a

INNER JOIN vbak AS b ON a_{vbeln = b}vbeln

WHERE b~erdat IN my_erdat

GROUP BY a~matnr.

APPEND it.

ENDSELECT.

LOOP AT it.

WRITE :/ it-matnr, it-kbmeng.

ENDLOOP.