Other commentor brings up a good point though - how do we efficiently get the balance of a certain account at a certain date time? Does using a ledger require constantly summing up columns? What happens when we have 1M, 10M, or 100M+ records?
Maybe the ledger would need to be broken into separate "completed" or "sealed" groups once we verify the balance is zero, so like the other commenter mentioned, we could have "checkpoints" where the balance is known to be zero and can calculate from that point forward, instead of from record 0.
And you are certain about going 1 month (or period) going back that at a particular date, at he last entry the balance was something.
Same as in paper books. Just see page total of that particular date....
This depends on how you implement the ledger. For pgledger, I store the balance in every entry, so to find a historical balance, you just need to find the most recent entry before that time:
https://github.com/pgr0ss/pgledger/blob/df5541dcf25f416a6a24...
I have a mental TODO to add a query function to make this simpler.
Generally, the most practical way to do is to "finalize" a number periodically (monthly and annually) when the books for the prior period have been "closed" (locked from further edits) and then sum only transactions taking place since the last closed balance. Most major ERPs do this.
Is this a good abstraction?
