Use Cases

Real-world scenarios where monetary prevents bugs and simplifies your code.

E-Commerce

Multi-currency catalogs, tax calculations, checkout totals

Financial Reporting

Revenue consolidation, MoM comparisons, FX exposure

Travel & Expense

Multi-currency receipts, reimbursement calculations

Crypto Portfolios

BTC/ETH holdings with satoshi-level precision

E-Commerce

Multi-Currency Product Catalog

DuckDB

CREATE TABLE products ( id INTEGER, name VARCHAR, price monetary ); INSERT INTO products VALUES (1, 'Basic Widget', '29.99 EUR'), (2, 'Pro Widget', '49.99 EUR'), (3, 'Enterprise Widget', '199.99 EUR'); -- Show prices in multiple currencies SELECT name, price AS eur, price ->> 'USD' AS usd, price ->> 'GBP' AS gbp FROM products;

Run Reset

Order Totals with Tax

DuckDB

CREATE TABLE orders ( id INTEGER, subtotal monetary, tax_rate DECIMAL(5,2) ); INSERT INTO orders VALUES (1, '99.99 USD', 0.0875), (2, '149.99 USD', 0.0875), (3, '299.99 USD', 0.0875); -- Calculate tax and total SELECT id, subtotal, subtotal * tax_rate AS tax, subtotal * (1 + tax_rate) AS total FROM orders;

Run Reset

Financial Reporting

Revenue by Region

CREATE TABLE revenue (
    region VARCHAR,
    amount monetary,
    period DATE
);

INSERT INTO revenue VALUES
    ('North America', '1500000 USD', '2025-01-01'),
    ('Europe', '1200000 EUR', '2025-01-01'),
    ('Asia Pacific', '180000000 JPY', '2025-01-01');

-- Convert all to USD for consolidated reporting
SELECT
    region,
    amount,
    amount ->> 'USD' AS amount_usd
FROM revenue
ORDER BY monetary_decimal(amount ->> 'USD') DESC;

Month-over-Month Comparison

WITH monthly AS (
    SELECT
        DATE_TRUNC('month', order_date) as month,
        monetary_sum(total) as revenue
    FROM orders
    WHERE monetary_currency(total) = 'EUR'
    GROUP BY DATE_TRUNC('month', order_date)
)
SELECT
    month,
    revenue,
    LAG(revenue) OVER (ORDER BY month) as prev_month,
    (monetary_decimal(revenue) - monetary_decimal(LAG(revenue) OVER (ORDER BY month)))
        / monetary_decimal(LAG(revenue) OVER (ORDER BY month)) * 100 as growth_pct
FROM monthly;

Travel & Expense

Multi-Currency Expense Reports

DuckDB

CREATE TABLE expenses ( id INTEGER, description VARCHAR, amount monetary, country VARCHAR ); INSERT INTO expenses VALUES (1, 'Hotel Berlin', '250 EUR', 'DE'), (2, 'Flight to Tokyo', '1200 USD', 'US'), (3, 'Dinner Tokyo', '8500 JPY', 'JP'), (4, 'Taxi London', '45 GBP', 'GB'); -- Group by currency SELECT monetary_currency(amount) as currency, COUNT(*) as items, monetary_sum(amount) as total FROM expenses GROUP BY monetary_currency(amount);

Run Reset

Expense Reimbursement in Home Currency

-- Set up exchange rates
CREATE TABLE exchange_rates AS
SELECT 'EUR' as currency_from, 'USD' as currency_to, 1.085 as rate, NOW() as valid_from
UNION ALL SELECT 'EUR', 'GBP', 0.845, NOW()
UNION ALL SELECT 'EUR', 'JPY', 162.5, NOW();

SET monetary_exchange_table = 'exchange_rates';

-- Calculate reimbursement in employee's home currency (EUR)
SELECT
    description,
    amount,
    amount ->> 'EUR' AS reimbursement_eur
FROM expenses;

Cryptocurrency Portfolio

Mixed Crypto Holdings

DuckDB

CREATE TABLE crypto_holdings ( wallet VARCHAR, asset monetary ); INSERT INTO crypto_holdings VALUES ('hot', '0.5 BTC'), ('hot', '2.5 ETH'), ('cold', '1.0 BTC'), ('cold', '10.0 ETH'); -- Sum by asset type SELECT monetary_currency(asset) as currency, monetary_sum(asset) as total_holdings FROM crypto_holdings GROUP BY monetary_currency(asset);

Run Reset

Subscription Business

MRR by Plan

DuckDB

CREATE TABLE subscriptions ( customer_id INTEGER, plan VARCHAR, mrr monetary ); INSERT INTO subscriptions VALUES (1, 'starter', '9.99 USD'), (2, 'pro', '29.99 USD'), (3, 'pro', '29.99 USD'), (4, 'enterprise', '99.99 USD'), (5, 'starter', '9.99 USD'); -- MRR breakdown SELECT plan, COUNT(*) as customers, monetary_sum(mrr) as total_mrr, monetary_avg(mrr) as avg_mrr FROM subscriptions GROUP BY plan ORDER BY monetary_decimal(monetary_sum(mrr)) DESC;

Run Reset

Anti-Patterns to Avoid

Don’t: Mix Currencies Without Converting

-- This will error (correctly!)
SELECT SUM(amount) FROM expenses;
-- Error: cannot sum EUR and USD: currency mismatch

-- Do this instead:
SELECT monetary_sum(amount ->> 'EUR') FROM expenses;

Don’t: Store Amount and Currency Separately

-- Bad: two columns, no type safety
CREATE TABLE bad_prices (
    amount DECIMAL(10,2),
    currency VARCHAR(3)
);

-- Good: single monetary column
CREATE TABLE good_prices (
    amount monetary
);

Don’t: Use FLOAT for Money

DuckDB

-- Floating point errors accumulate SELECT 0.1 + 0.2 = 0.3 AS float_math;

Run Reset

DuckDB

-- Monetary uses integer storage SELECT '0.10 USD'::monetary + '0.20 USD'::monetary = '0.30 USD'::monetary AS monetary_math;

Run Reset

Summary

Use Case	Key Benefit
E-commerce	Multi-currency catalogs with safe arithmetic
Financial reporting	Currency conversion with auditable rates
Travel expenses	Automatic currency handling by country
Cryptocurrency	Sub-cent precision (8 decimals for BTC)
SaaS billing	Consistent MRR calculations
Double-entry ledgers	Currency validation in aggregates