Should credits be stored as negative numbers in a double-entry bookkeeping database? Assuming you use a table structure like:

Journal Entries

JournalEntryID
AccountingPeriodID
TimeStamp


Journal Entry Lines

JournalEntryLineID (UID)
JournalEntryID (Foreign to Journal Entries)
AccountID
Amount


Does it make sense to use negative numbers in the amount column to represent credits? If you used negative numbers for credits and positive numbers for debits, it would be easy to check the integrity of all the records just by getting the SUM() of Amount for all records in the Journal Entry Lines table (it should be zero at all times).

Paper journals don't use signed numbers though since the sign is implicit. And other systems I've looked at have used positive amounts for both. Would it be good practice to use signed amounts or are there pitfalls to this approach?
I've worked for a long time with a range of different types of accounting systems (albeit predominantly with European accounting standards) and the norm is that you use positive numbers for debit entries and negative numbers for credit entries. This means that your assets are positive and your liabilities negative, but your income is negative and costs are positive. So when you're building income statement-related reports you'll need to invert the numbers.

I've seen instances of systems that use separate columns for debit and credit, but to me that is just anti-normalization. Typically, most of those systems also provide a "total" column, which is positive in debit and negative in credit.

As you say, this way every transaction has to balance out to zero (you can probably write some type of constraint to make sure it does).