This is what I posted on the MS forum for SQL Server in response to this column:
I think enums would be a great feature to add to SQL. I would think they would work best like a custom datatype.
Something like this:
exec sp_addenum 'Visa', 0, 'PaymentType'
exce sp_addenum 'MasterCard', 1, 'PaymentType'
exec sp_addenum 'Amex', 5, 'PaymentType'
Then you would use it in a table as:
create table Orders (
OrderID bigint not null identity(1,1),
CustomerID bigint not null,
PaymentMethod PaymentType not null
The underlying datatype should be a bigint - allowable to be compared to other integer values so that they could be passed in from other sources.
Then in queries like suggested:
select * from Orders where PaymentMethod in (PaymentType.Visa, PaymentType.MasterCard)
The question would be is something like this allowed?
select * from Orders where PaymentMethod = Shipping.UPS
I think it should be prohibited. Either a constant (PaymentMethod = 1) or a valid enum type (PaymentMethod = PaymentType.Visa) or a variable (PaymentMethod = @PaymentType) should be accepted.
This would hopefully at least prevent people from writing the PaymentMethod = Shipping.UPS code.