Evidently never heard of twos compliment.

As Lynn Pettis wrote:

"Not all credits are negative. It depends if they are expenses, liabilities, or assests."

Thus it makes no sense not to allow negative values. Thus even splitting into debits and credits you'll need a sign column.

The problems with the design as I see it will be when you want to sum, average, etc. the values. The only way I can see you'll be able to do it with the design constraint you've been given is to setup a cursor to loop through each value and if the sign value is positive leave the value alone, and if the sign value is negative then you'll need to times the amount by -1. Seems like a massive performance hit for no good reason, and one that you'll eventually probably have to revert anyway.

Who was the numbskull who came up with that design? Were they a DBA - or even someone with any programming experience at all?