query group and Sum number has got Conditional ?

Question

I have the following SQL Server query:

requirements SUM and GROUP column SOLUONG AS SL , if TRAHANG = true then bring positive column opposite quantity quantity column value is negative, no team and no columns SL sum is, if I would give TRAHANG column in the SELECT statement error. Can you help me ?

[CODE]

//Query warning eror

SELECT TABHDBHCT.MAVACH_SP, TABHDBHCT.TENSP, SUM(TABHDBHCT.SOLUONG)*CASE WHEN [TRAHANG] = 0 THEN 1 ELSE -1 END AS SL

FROM TABHDBHCT INNER JOIN

TABHDBH ON TABHDBHCT.MASOPHIEU = TABHDBH.IDSOPHIEU

WHERE (TABHDBH.TTTHANHTOAN = 1 OR

TABHDBH.TTTHANHTOAN = 2) AND (TABHDBH.NGAY BETWEEN '11/01/2016' AND '11/30/2016')

GROUP BY TABHDBHCT.MAVACH_SP, TABHDBHCT.TENSP

ORDER BY TABHDBHCT.TENSP;

[/CODE]