-- Prepare sample data 
DECLARE	@Base TABLE (ID INT, Data INT) 

INSERT  @Base 
SELECT  1, 1 UNION ALL 
SELECT  2, 1 

DECLARE @New TABLE (ID INT, Data INT) 

INSERT  @New 
SELECT  1, 0 UNION ALL 
SELECT  2, 1 UNION ALL 
SELECT  2, 1 UNION ALL 
SELECT  3, 1 

-- Before
SELECT	*
FROM	@Base

-- Do the magic
MERGE   @Base AS b 
USING   ( 
                SELECT          ID, 
                                SUM(Data) 
                FROM            @New 
                GROUP BY        ID 
        ) AS src (ID, Data) ON src.ID = b.ID 
WHEN    MATCHED AND src.Data = 0 
        THEN DELETE
WHEN    MATCHED 
        THEN UPDATE SET b.data = src.Data
WHEN    NOT MATCHED THEN 
        INSERT (ID, Data) VALUES (src.ID, src.Data); -- Last statement must end with a comma

-- After
SELECT	*
FROM	@Base

ID  Data
--  ----
1   1
2   1

ID  Data
--  ----
2   2
3   1