Adjust a member's balance without losing the trail
Every manual adjustment writes a ledger row and an audit row, inside one transaction. An admin panel that edits a balance directly is how books stop balancing.
Tagged “balances”
3 entries
Guard against a negative balance, and claw back correctly
Make the column unsigned, check inside the transaction, and let a clawback take a balance to zero rather than below it.
Move balance between two accounts without losing any
Lock both rows in a fixed order, check inside the transaction, and write a ledger entry for each side. Skipping any of the three is how balances drift.