mysql里记录货币

CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    amount DECIMAL(10, 2)
);

INSERT INTO orders (order_id, amount) VALUES (1, 100.50);
INSERT INTO orders (order_id, amount) VALUES (2, 50.25);

SELECT SUM(amount) AS total_amount FROM orders;

CREATE TABLE exchange_rates (
    from_currency VARCHAR(3),
    to_currency VARCHAR(3),
    rate DECIMAL(10, 4),
    PRIMARY KEY (from_currency, to_currency)
);

INSERT INTO exchange_rates (from_currency, to_currency, rate) VALUES ('USD', 'EUR', 0.85);

SELECT 
    o.order_id,
    o.amount AS amount_usd,
    (o.amount * er.rate) AS amount_eur
FROM orders o
JOIN exchange_rates er ON o.currency = er.from_currency AND 'EUR' = er.to_currency;