con los datos que mencionas puedes hacer esto :)
Código SQL:
Ver originalCREATE TABLE #temp
(
articulo INT,
depo INT,
cant INT,
mes INT,
signo INT
)
INSERT INTO #temp VALUES (1,1 ,10, 3, -1)
INSERT INTO #temp VALUES (1, 1, 15, 3, -1)
INSERT INTO #temp VALUES (1, 1, 20, 4, 1)
INSERT INTO #temp VALUES (1, 2, 15, 6, 1)
INSERT INTO #temp VALUES (2, 2, 12, 6, 1)
INSERT INTO #temp VALUES (2, 3, 12, 7, 1 )
INSERT INTO #temp VALUES (2, 3, 15, 7, -1)
SELECT articulo,depo,mes,SUM(cantidad) AS total FROM(
SELECT articulo,depo,mes,(cant*signo) AS cantidad FROM #temp) AS t1 GROUP BY articulo,depo,mes
saludos!