mysql 求两个日期差

DATEDIFF(date1, date2)

CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    order_date DATE
);

INSERT INTO orders (order_id, order_date) VALUES
(1, '2023-01-01'),
(2, '2023-01-05'),
(3, '2023-01-10');

SELECT DATEDIFF('2023-01-10', '2023-01-01') AS days_diff;

SELECT DATEDIFF('2023-01-10', '2023/01/01') AS days_diff; -- 错误示例
SELECT DATEDIFF('2023-01-10', '2023-01-01') AS days_diff; -- 正确示例

SELECT DATEDIFF('2023-01-01', '2023-01-10') AS days_diff; -- 结果将是 -9

SELECT DATEDIFF(order_date, '2023-01-01') AS days_diff
FROM orders
WHERE order_date IS NOT NULL;