Question

我有此存储过程，希望它返回一个值（lastinsertid）。它返回的所有内容均为0。我的问题是下面的代码怎么了？

CREATE PROCEDURE my_stored_procedure(
    IN inCartId int
)
BEGIN

    DECLARE orderId INT;

    -- Insert a new record into orders and obtain the new order ID
    INSERT INTO orders (created_on) VALUES (NOW());

    -- Obtain the new Order ID
    SELECT LAST_INSERT_ID() INTO orderId;

    -- Insert order details in order_detail table
    INSERT INTO order_detail (
        order_id, product_id, attributes, product_name, quantity, unit_cost
    )
    SELECT
        orderId,
        p.id,
        sc.attributes,
        p.name,
        sc.quantity,
        COALESCE( NULLIF( p.discounted_price, 0 ), p.price ) AS unit_cost
    FROM
        shopping_cart sc
        INNER JOIN products p ON sc.product_id = p.id
    WHERE
        sc.cart_id = inCartId
        AND
        sc.buy_now;

    -- Save the order's total amount
    UPDATE
        orders
    SET
        total_amount = (
            SELECT
                SUM( unit_cost * quantity )
            FROM
                order_detail
            WHERE
                order_id = orderId
        )
    WHERE
        id = orderId;

    -- Clear the shopping cart
    CALL shopping_cart_empty( inCartId );

END

Answer 1

在大多数数据库系统（例如MySQL / MariaDB和MS SQL Server）中，存储过程没有“返回值”，就像函数一样。
相反，存储过程通过输出参数将数据返回给其调用方。
- 在MySQL中，FUNCTION 确实返回值_{，但是FUNCTION与存储过程不同，解释上的差异最好在单独的问题中完成< / sub>。}
（在Microsoft SQL Server和Sybase中，存储过程都返回单个int “返回代码”值，但是该值指示状态（例如可执行程序如何具有退出代码），并不意味着要用于从数据库中返回数据。）
要在MySQL和MariaDB中使用输出参数，请使用OUT关键字而不是IN关键字，然后分配给该参数。

在您的情况下，用我在存储过程参数列表中添加的orderId参数替换局部变量OUT newOrderId。无需其他更改。

CREATE PROCEDURE my_stored_procedure(
    IN inCartId int,
    OUT newOrderId int
)
BEGIN

    -- Insert a new record into orders and obtain the new order ID
    INSERT INTO orders (created_on) VALUES (NOW());

    -- Obtain the new Order ID
    SELECT LAST_INSERT_ID() INTO newOrderId;

    -- Insert order details in order_detail table
    INSERT INTO order_detail (
        order_id, product_id, attributes, product_name, quantity, unit_cost
    )
    SELECT
        orderId,
        p.id,
        sc.attributes,
        p.name,
        sc.quantity,
        COALESCE( NULLIF( p.discounted_price, 0 ), p.price ) AS unit_cost
    FROM
        shopping_cart sc
        INNER JOIN products p ON sc.product_id = p.id
    WHERE
        sc.cart_id = inCartId
        AND
        sc.buy_now;

    -- Save the order's total amount
    UPDATE
        orders
    SET
        total_amount = (
            SELECT
                SUM( unit_cost * quantity )
            FROM
                order_detail
            WHERE
                order_id = orderId
        )
    WHERE
        id = orderId;

    -- Clear the shopping cart
    CALL shopping_cart_empty(inCartId);

END

存储过程应该在什么时候不返回任何值（MySQL）

1 个答案: