Using two positive numbers preserves some information, but still destroys plenty. Just less than a single signed number would. Consider two accounts:
1. An account A with a debit balance of $1m and a credit balance of $0, and
2. An account B with a debit balance of $1m and a credit balance of $0.
One of those was opened by a lottery winner last week who did a single transaction dropping in their winnings. The other was opened by a retiree 60 years ago who has been dripping small deposits in for their entire working history. Which is which?
That distinction is still lost by summing debits and summit credits.
To really preserve information, you'd need the full list of all transactions. But, obviously, that comes at a significant performance cost. So the way to look at storing sums for debits and credits is that it's a trade-off which gives you a little more information than just a single balance but is still a relatively small fixed-size amount of data.
Using two positive numbers preserves some information, but still destroys plenty. Just less than a single signed number would. Consider two accounts:
One of those was opened by a lottery winner last week who did a single transaction dropping in their winnings. The other was opened by a retiree 60 years ago who has been dripping small deposits in for their entire working history. Which is which?That distinction is still lost by summing debits and summit credits.
To really preserve information, you'd need the full list of all transactions. But, obviously, that comes at a significant performance cost. So the way to look at storing sums for debits and credits is that it's a trade-off which gives you a little more information than just a single balance but is still a relatively small fixed-size amount of data.