Using Merge in SQL Server 2008 R2

MERGE INTO [TARGETTABLE] AS Target
    USING [SOURCETABLE] AS SOURCE
    ON
        –unique key filtering condition
        Target.COLUMN1=SOURCE.COLUMN1 AND
        Target.COLUMN2=SOURCE.COLUMN2 AND
        Target.COLUMN3 =SOURCE.COLUMN3 AND
        Target.COLUMN4 =SOURCE.COLUMN4
     WHEN MATCHED THEN
        –update or delete query
        UPDATE SET
            Target.ColumnA=SOURCE.ColumnA,
            Target.ColumnB=SOURCE.ColumnB,
            Target.ColumnC=SOURCE.ColumnC

    WHEN NOT MATCHED THEN
        –INSERT QUERY
        INSERT (COLUMNA, ColumnB, ColumnC, ColumnD)
        VALUES(
                        SOURCE.ColumnA,
                        SOURCE.ColumnB,
                        SOURCE.ColumnC,
                        SOURCE.ColumnD                    )
    ;