I completely agree with this statement. Never store values used in financial calculations as floating point values, because a floating point is an approximate representation of a decimal value, stored as binary. In most cases it is inaccurate as soon as you store it. You can read more in this excellent — if a little dry — technical paper.
With that out of the way, we get into an interesting discussion about the correct data type to store currency values.
Randolph states an argument around why
DECIMAL(19,4) is fine. And it’s great for most cases, though the one “real” financial system I’ve worked with have money stored as integer types (with SQL Server, that’d be
BIGINT) because of precision, especially when working with exchange rates. But for most cases—especially when you’re not building the system of record for financial transactions or accounts—I agree with Randolph that
DECIMAL is fine. Dave Wentzel has a great comment explaining even further the reasoning behind integer values for certain monetary columns.