Should you choose the MONEY or DECIMAL(x,y) datatypes in SQL Server?

Question

I\'m curious as to whether or not there is a real difference between the money datatype and something like decimal(19,4) (which is what money uses

Answer 1

We've just come across a very similar issue and I'm now very much a +1 for never using Money except in top level presentation. We have multiple tables (effectively a sales voucher and sales invoice) each of which contains one or more Money fields for historical reasons, and we need to perform a pro-rata calculation to work out how much of the total invoice Tax is relevant to each line on the sales voucher. Our calculation is

vat proportion = total invoice vat x (voucher line value / total invoice value)

This results in a real world money / money calculation which causes scale errors on the division part, which then multiplies up into an incorrect vat proportion. When these values are subsequently added, we end up with a sum of the vat proportions which do not add up to the total invoice value. Had either of the values in the brackets been a decimal (I'm about to cast one of them as such) the vat proportion would be correct.

When the brackets weren't there originally this used to work, I guess because of the larger values involved, it was effectively simulating a higher scale. We added the brackets because it was doing the multiplication first, which was in some rare cases blowing the precision available for the calculation, but this has now caused this much more common error.