My guess is that there would be very little difference in performance between the two expressions, unless the columns x1, x2, etc. contain more than one datatype. If that's the case, you would lose performance by needing to do implicit datatype conversions. The result would be superior performance by 'sum(x1) + sum(x2)+ ...', which needs to do the conversion only once after computing all the row sums. 'Sum(x1+x2+..)', on the other hand, would need to do type conversions for every row being processed.