ORIGINAL COMPANY-CONTEXT PRACTICE
Aggregate a ledger without mixing currencies
Original practice scenario inspired by Mitsubishi UFJ Financial Group, Inc.'s public business context; this is not a reported interview question or a description of its internal systems. A fictional financial group has signed ledger entries in several currencies and a daily exchange-rate table. Explain how to report native-currency balances and a separately labeled converted total without multiplying entries or silently using missing rates.
Written for independent practice using company context; this is not a verified question from a company interview.
A REASONED APPROACH
Model answer.
Preserve currency as part of the balance grain. Native amounts in different currencies cannot be added meaningfully, and conversion requires a specific rate date, direction, and rounding convention.
Work through it
- Aggregate ledger entries by account and currency first. Validate that rate data has one row per required currency pair and valuation date.
- Join the aggregate to that unique rate set and expose missing rates as an exception or incomplete valuation, rather than substituting zero.
- Compute the converted measure with fixed-decimal or integer minor-unit handling, applying the documented rounding stage. Reconcile native totals before checking the converted report.
Tradeoffs to discuss
- Converting each transaction and converting a final balance can differ because of valuation timing and rounding. The report must state which interpretation it implements.
Common pitfalls
- Duplicate rate rows multiply balances.
- A bare SUM(amount) across currencies produces a number without a coherent unit.