MERGE dbo.SomeTable AS target       


USING dbo.AnotherTable AS source    


ON (target.[UserName] = source.[UserName])


WHEN MATCHED THEN                           
    UPDATE SET Name = source.Name,
               Col = source.Col


WHEN NOT MATCHED THEN  
    INSERT (Col1, Col2, ...., ColN)  
    VALUES (source.Val1, source.Val2, ...., source.ValN);