Accounting Schema

Hi all,

Can anyone out there with more experience than me give me some hints as to
how to do accounting tables in a db. The problem I am wrestling with is how
to represent credits, and debits.
One way is to identify credits and debits with a transactiontype, and keep
all of the numbers positive which models the way accountants do it. This
makes things liking calculating the balance difficult with a sql statement.

Any hints would be appreciated.

Dave