Some thoughts.
The current MONEY type might be considered akin to ASCII.
Perfect for a base US centric accounting system where there are
cents and dollars and no need to carry smaller fractions. As
discussed, there are some details that could be refined.
When it comes to this type being used in full blown money
systems it lacks the ability to carry fractions of cents and
keep track of currencies. It also needs to play nicer with other
exact types such as numeric, i.e., no intermediate calculations
as real.
Therefore the discussion is really about the desired role for
the MONEY type. Should it be refined in its current dallar and
cents mode? or, be promoted to a more universal role (akin to a
shift from ASCII to UTF)?
If there is merit in making MONEY work for most situations
involving financial transactions I think the following might apply:
- keep integer as the underlying base type (for performance)
- generalise the decimal multiplier of a MONRY column so a
specific MONEY column can be what its creator wants (from
partial cents to millions of dollars/Yen/Other, along with
rounding/truncating rules as required by r the user of his/her
external agencies)
- define the currency for a given column and only allow this to
change in defined ways, and specifically forbid implicit changes
such as would arise from altering LOCALE information
- ensure the MONEY type plays nice with other exact precision
types, i.e., convert to REAL/FLOAT as a very last resort
Personally I don't think it is appropriate for the MONEY type to
have variable characteristics (such as different currencies)
within a given column, rather the column variable should define
the currency along with the desired decimal-multiplier and
whatever else is required. The actual values within the column
remain as simple integers. This is mostly based on performance
issues. If the MONRY type is to be used it has to offer real
performance benefits over bespoke NUMERIC applications.
Regards
Gavan Schneider