MySQL存储过程终止执行的三种常见方法

DELIMITER //
CREATE PROCEDURE process_order(IN order_id INT)
main: BEGIN
    -- 校验订单是否存在
    IF NOT EXISTS (SELECT 1 FROM orders WHERE id = order_id) THEN
        LEAVE main; -- 直接退出存储过程
    END IF;
 
    -- 校验库存
    IF (SELECT stock FROM inventory WHERE product_id = (
        SELECT product_id FROM orders WHERE id = order_id
    )) <= 0 THEN
        LEAVE main; -- 提前终止
    END IF;
 
    -- 扣库存
    UPDATE inventory
    SET stock = stock - 1
    WHERE product_id = (SELECT product_id FROM orders WHERE id = order_id);
 
    -- 更新订单状态
    UPDATE orders
    SET status = 'processed'
    WHERE id = order_id;
END //
DELIMITER ;

DELIMITER //
CREATE PROCEDURE validate_user(IN user_id INT)
BEGIN
    IF NOT EXISTS (SELECT 1 FROM users WHERE id = user_id) THEN
        SIGNAL SQLSTATE '45000'
            SET MESSAGE_TEXT = '用户不存在';
    END IF;
 
    UPDATE users SET last_login = NOW() WHERE id = user_id;
END //
DELIMITER ;

CALL validate_user(999);
-- ERROR 1644 (45000): 用户不存在

CREATE PROCEDURE simple_check(IN value INT)
BEGIN
    IF value > 0 THEN
        UPDATE logs SET message = '有效值' WHERE id = 1;
    END IF;
END;

DELIMITER //
CREATE PROCEDURE handle_payment(IN order_id INT)
main: BEGIN
    -- 校验订单
    IF NOT EXISTS (SELECT 1 FROM orders WHERE id = order_id) THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = '订单不存在';
    END IF;
 
    -- 校验库存
    IF (SELECT stock FROM inventory WHERE product_id = (
        SELECT product_id FROM orders WHERE id = order_id
    )) <= 0 THEN
        LEAVE main; -- 无库存，直接退出，不算异常
    END IF;
 
    -- 业务逻辑
    UPDATE inventory SET stock = stock - 1 WHERE product_id = (
        SELECT product_id FROM orders WHERE id = order_id
    );
 
    UPDATE orders SET status = 'paid' WHERE id = order_id;
END //
DELIMITER ;