Pulling gridview with query

DECLARE @IncommingT1 AS TABLE (C1 VARCHAR(64), Data int)
DECLARE @OutGoingT2 AS TABLE (C1 VARCHAR(64), Data int)

INSERT INTO @IncommingT1
(
    C1,
    Data
)
VALUES
(   'product1', -- C1 - varchar(64)
    5   -- Data - int
),(   'product2', -- C1 - varchar(64)
    3   -- Data - int
),(   'product2', -- C1 - varchar(64)
    4   -- Data - int
),(   'product1', -- C1 - varchar(64)
    3   -- Data - int
);
INSERT INTO @OutGoingT2
(
    C1,
    Data
)
VALUES
(   'product1', -- C1 - varchar(64)
    3   -- Data - int
),(   'product2', -- C1 - varchar(64)
    3   -- Data - int
),(   'product1', -- C1 - varchar(64)
    4   -- Data - int
),(   'product2', -- C1 - varchar(64)
    2   -- Data - int
)

SELECT it.C1,(SUM(DISTINCT it.Data)) - (SUM(DISTINCT ogt.Data)) AS C2  FROM  @IncommingT1 AS it 
LEFT JOIN @OutGoingT2 AS ogt ON ogt.C1 = it.C1
GROUP BY it.C1,ogt.c1